Chapter 27

Neurosurgery

Allan J. Hamilton

Martin Weinand

I Introduction

Neurosurgery is surgical management of nervous system disease. The 1990s have seen rapid expansion and application of innovative technologies, including magnetic resonance imaging (MRI) and angiography for detecting lesions of the brain and spinal cord; positron emission tomography (PET) for evaluation of metabolic defects in the brain; and minimally invasive techniques such as implantable deep brain stimulators, interventional radiology for aneurysms, and radiosurgery. There have also been refinements of operative tools, including the computed/imageguided neuronavigation operating microscope, the ultrasonic aspirator, and the laser.

II Anatomy

The brain accounts for only 2% of the body weight but requires 18% of the cardiac output and 20% of the oxygen used by the body. The normal cerebral blood flow is about 50 mL/100 g of brain tissue per minute.

A Arterial supply to the brain

The anterior circulation is derived from the two internal carotid arteries , giving rise to the middle cerebral and the smaller anterior cerebral arteries. These vessels supply mainly the frontal, temporal, and parietal lobes as well as the deep gray matter.

The posterior circulation is comprised of the two vertebral arteries.

At the caudal margin of the pons, the arteries unite to form the basilar artery.

The basilar artery gives off branches supplying the pons, cerebellum, thalamus, and dividing into the posterior cerebral arteries, it supplies the occipital lobes.

The circle of Willis , an arterial circle, is formed by communicating arteries between the major branches of the anterior and posterior circulations. In the event of a trunk vessel occlusion, the blood supply to its territory may be supplied by another vessel via the circle of Willis.

B Venous return to the brain

Superficial cerebral veins drain the cortex and subcortical white matter and drain into the superior sagittal sinus or the basal sinuses (i.e., the transverse, petrosal, or cavernous sinuses).

Deep cerebral veins drain the deeper structures (nuclei). The deep veins consist of the paired internal cerebral and basal (Rosenthal) veins, which form the great vein of Galen before emptying into the straight sinus.

All venous blood from the brain returns to the heart via the internal jugular veins.

Sampling of blood from the jugular bulb provides an estimate of cerebral metabolism.

C Arterial supply to the spinal cord

The spinal cord is supplied by the anterior spinal artery and the paired posterior spinal arteries , reinforced by the segmental radicular arteries.

The anterior spinal artery branches into the anterior sulcal artery in the anterior sulcus, which supplies the anteromedial gray matter.

The segmental arteries are important because their interruption can lead to infarction of the spinal cord.

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D

Venous return from the spinal cord parallels the arterial supply.

Anterior longitudinal venous trunks drain corresponding areas of the cord and are drained, in turn, by 6– 11 radicular veins into the epidural venous plexus.

Posterior longitudinal venous trunks drain the posterior funiculus, the posterior horns, and the white matter in the lateral funiculi. These trunks, in turn, are drained by 5–10 radicular veins into the epidural venous plexus.

The epidural venous plexus is located between the vertebral periosteum and the dura mater.

The plexus consists of two or more anterior and posterior longitudinal veins interconnected at various levels.

At each intervertebral space, there is an extensive anastomosis with intercostal, thoracic, and abdominal veins.

None of these venous channels has valves, and thus, blood from these plexuses may directly enter the systemic circulation and vice versa.

E

Cerebrospinal fluid (CSF) brain tissue, and blood are the major components of the intracranial space.

Normally, the total volume of the CSF is about 150 mL, with 25 mL located in the ventricles. The CSF is formed at a rate of 0.35 mL/minute (approximately 150 mL three times per day). Roughly 80% of the CSF is produced by the choroid plexus, and the rest is secreted in the interstitial spaces of the brain.

The CSF flows from the lateral ventricles to the third ventricle through the foramina of Monro and reaches the fourth ventricle via the aqueduct of Sylvius and reaches the brain exterior by the foramina of Magendie (midline) and Luschka (lateral).

The CSF circulates around the spinal cord and the brain and is reabsorbed into the superior sagittal sinus via the arachnoid villi. Some of the CSF is absorbed around the spinal nerve roots.

The arachnoid villi act as one -way valves, and they open at a pressure of 5 mm Hg.

F Functional anatomy of the nervous system

The following principles form the basis for evaluating and treating neurologic disease.

Pathophysiologic processes unique to the nervous system result from the:

Complexity of the functional organization of the nervous system

Rigidity of the bony enclosures of the brain and spinal cord

Responses of the nervous system to injury

Focal lesions affect neurologic function by:

Local destruction of brain tissue

Tissue distortion with functional loss attributable to axonal stretching and subsequent synaptic damage

Changes in local blood flow, causing ischemia or venous congestion

Alterations in the electrical or metabolic activity of a local area, producing an epileptic focus

Location of the lesion

A small focal lesion in the brain stem can produce devastating effects.

A similar lesion in the frontal (silent) area may produce no significant neurologic deficit.

III Pathophysiology

A Cerebral edema

The brain reacts to insults by developing edema. Acute edema causes more deterioration in neurologic function than does chronic edema. The rate of edema formation is directly proportional to the neurologic deficits.

Types of cerebral edema

Cytotoxic edema is a result of depletion of neuronal glucose and oxygen stores. It is most commonly seen after cerebral infarction and may occur in association with Reye's syndrome. The blood–brain barrier is preserved.

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Vasogenic edema (also called extracellular white matter edema) results from a breakdown of the blood–brain barrier and leakage of plasma into the extracellular spaces. This is the most common type of edema seen clinically and may be caused by trauma, brain tumor, infection, surgery, and systemic hypertonicity, such as that due to use of mannitol.

Mechanisms by which edema alters neuronal and axonal function include:

Ischemia that occurs as increased intracranial pressure (ICP) compromises cerebral perfusion

Decreased oxygen diffusion

Lipid peroxidation in membranes

B ICP

The skull , a rigid box with a volume of approximately 1900 mL, harbors three major components:

Approximately 85% is brain (5% is extracellular fluid, 45% is glial tissue, and 35% is neuronal tissue).

Approximately 7% is blood.

Approximately 7% is CSF.

Monro-Kellie hypothesis. Under normal conditions, these three components and the intracranial volume are in equilibrium, yielding normal ICP.

To maintain a normal ICP, a change in one component must be offset by compensatory changes in

fluid.

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Vomiting

Clouding of mentation

Papilledema

Paralysis of upward gaze (Parinaud's syndrome)

Sixth nerve palsy

Bulging fontanelles and splitting sutures (in infants)

Measurement of ICP

In clinical practice, ICP may be measured by ventriculostomy, intraparenchymal monitoring device, or subarachnoid bolt.

An estimate of ICP may also be made by lumbar puncture in the absence of space -occupying intracranial lesions.

Whereas intraparenchymal and subarachnoid bolt monitoring produce continuous ICP data, ventriculostomy monitoring produces both a continuous record of ICP and the therapeutic option of removing CSF to reduce ICP.

C Herniation

When all compensatory mechanisms have been exhausted and the ICP continues to increase, the brain “herniates” or shifts toward the low -pressure compartment (the falx and the tentorium divide the interior of the skull into compartments). Various herniation syndromes are recognized.

Subfalcine herniation is a displacement from one supratentorial compartment to another underneath the falx. It may lead to loss of function in the opposite leg, loss of bladder control, or both.

Transtentorial (uncal) herniation

This is the most common type of brain herniation seen clinically and occurs when the medial temporal lobe of one or both hemispheres is forced down over the edge of the tentorium.

Uncal herniation may occur as a result of diffuse brain swelling or of a supratentorial mass lesion.

Neurologic signs are:

Progressive deterioration of consciousness

Ipsilateral pupillary dilatation from oculomotor nerve compression by the herniating gyri

Contralateral hemiparesis as a result of compression of the cerebral peduncles

Hemiparesis is ipsilateral in 50% of the cases, whereas pupillary dilatation is ipsilateral in 80%.

Thus, pupillary dilatation is more reliable in localizing the lesion. In 20% of the cases, the pupillary dilatation is opposite and hemiparesis is ipsilateral to the lesion—a false localizing sign known as the

Kernohan -Woltman notch phenomenon (Kernohan's notch).

Transforamen magnum herniation. The cerebellar tonsils herniate through the foramen magnum. The resulting medullary compression may elicit a Cushing's response (i.e., hypertension, bradycardia, and apnea) and ultimately leads to death.

D Cerebral blood flow, autoregulation, and CPP

Overview (Fig. 27 -2)

The average cerebral blood flow normally ranges between 50 and 55 mL/100 g of brain tissue per minute , with the gray matter having a higher flow (i.e., 75 mL/100 g/minute) than the white matter (25 mL/100 g/minute).

The blood flow is coupled to the local metabolic demands and is highest where the density of synapses is greatest (termed metabolic autoregulation ).

The flow is directly proportional to the mean arterial pressure (MAP) and the vessel radius (r)(Q

MAP × r4 , Poiseuille's law ), and it is inversely proportional to the blood viscosity and vessel length. These factors can be manipulated to improve cerebral blood flow.

Pressure autoregulation describes the observation that normally over a wide range of mean arterial pressure (50–150 mm Hg), the cerebral blood flow remains unchanged at 50 mL/100 g of brain tissue per minute (Fig. 27 -2).

This may change focally or globally as a result of head injury, subarachnoid hemorrhage (SAH), stroke, or a brain tumor.

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FIGURE 27-2 Cerebral blood flow versus cerebral perfusion pressure. Note that normal autoregulation that occurs for cerebral perfusion pressure is 50–150 mm Hg.

In the patient with intact autoregulation, ICP remains stable as blood pressure changes within the limits above.

However, if the ICP passively follows the arterial pressure, it is indicative of impaired autoregulation

Lesions in the midbrain can cause central neurogenic hyperventilation (deep breathing at a very fast rate) that may lead to severe alkalosis.

Lesions in the lower pons can cause apneusis , which is complete cessation of involuntary breathing, leading to respiratory arrest during sleep (Ondine's curse).

Medullary lesions can lead to various types of abnormal breathing patterns, which include:

Cluster breathing (a disorderly sequence of clusters of breaths with irregular pauses)

Ataxic breathing (Biot's breathing—periodic breathing in which apneic periods are punctuated by a few irregular deep breaths, lacking the waxing and waning pattern of Cheyne - Stokes respiration)

Cheyne -Stokes respiration (see IV B 4 b)

Gasping (breathing in which both deep and shallow breaths occur randomly with haphazard intervening pauses and a slow respiratory rate, which may finally lead to apnea)

Kussmaul's respiration , deep rapid breathing similar to central neurogenic hyperventilation, usually occurs as a result of diabetic or uremic acidosis.

C Neurologic evaluation

A detailed neurologic evaluation may not be possible in some emergency situations, and a brief examination will have to suffice to assess the neurologic damage.

The level of consciousness should be determined first. Patients may present as:

Alert, awake, and oriented

Lethargic (i.e., sleepy but easily arousable)

Stuporous (i.e., responsive only to noxious stimuli)

Comatose (i.e., not responsive to noxious stimuli)

Examination of the pupils. The pupils are examined for their size and reaction to light, and the position and movement of the eyes are noted. A few general rules may be helpful in localizing a lesion.

When a lesion in the cortex is present, the size of the pupil may be 6 mm or larger, and there may be wandering or roving eye movements.

With a lesion in the basal ganglia , the pupils may range from 2–3 mm in size, and the eyes are deviated downward and inward.

A lesion in the midbrain may be associated with pupils that are 4–5 mm in size (midrange), and convergent nystagmus or nystagmus retractorius may be present.

A lesion in the pons may be associated with pinpoint pupils (1 mm) and with ocular bobbing.

When a lesion in the medulla is present, the pupils may be slightly small (2 mm), and there is downbeat nystagmus.

Brain stem reflexes , such as the oculocephalic (doll's eye) reflex and the caloric (oculovestibular) responses, are checked to rule out irreversible brain stem damage.

Motor examination is then performed. In a comatose patient, it may only be possible to assess the response to painful stimuli.

Sensory level determination is important in patients with spinal cord lesions (see VI E 3).

Deep tendon reflexes and plantar responses are checked to distinguish a lower motor neuron lesion from an upper motor neuron lesion.

V Head Injuries

A Incidence

Trauma is the leading cause of death in the United States in people between the ages of 1 and 44 years. In nearly 75% of all trauma -related fatalities, head injury contributes significantly to the outcome. Approximately 60,000 patients with severe head injuries reach a hospital alive each year; an equal number of patients die before receiving hospital care.

Prevention is the most important area of intervention in head trauma.

Drunk driving, as well as failure to use safety belts or motorcycle helmets, significantly contributes to the severity of head injury.

Care of the severely head-injured patient begins at the scene of the accident.

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To prevent serious exacerbation of brain injury, it is essential to establish a secured airway, provide adequate ventilation, and support the circulation.

Hypoxia, hypercapnia, and hypotension must be corrected.

Hypotonic intravenous solutions (e.g., 5% dextrose in water) must be avoided because they promote an osmotic gradient between the intravascular compartment and brain interstitial space, causing traumatic cerebral edema. Colloid solutions, such as albumin and blood products, are preferred.

B Classification

Brain injuries occurring after trauma can be classified as:

Primary, occurring instantaneously at the time of impact

Secondary , resulting from a chain of events triggered by the initial injury. If not controlled, secondary injuries lead to further damage through ischemia, hypoxia, or both.

Primary and secondary injuries can be either:

Nonhemorrhagic focal or diffuse edema

Hemorrhages

Intra -axial (i.e., intracerebral; within the brain substance)

Extra -axial (i.e., extracerebral; outside the brain parenchyma, such as epidural and subdural

hematomas)

C Initial management and assessment

Immediate care of a head trauma victim is not different from that of any other injured patient.

Priorities (A, B, C)

Establishment of adequate airway and ventilation (A—airway)

Control of hemorrhage (B—bleeding)

Maintenance of peripheral vascular circulation (C—circulation)

Volume replacement with colloids or blood products can be performed when necessary to reduce the risk that cerebral edema will develop or worsen.

Stabilization of the neck with a hard cervical collar is necessary in all patients.

10% of patients with severe head injuries have associated spinal cord injuries; thus, all patients with head injuries should be transported using SCI precautions.

Precautions include immobilization of the entire spine on a full spine board and use of a cervical collar.

Blood is drawn for typing and cross matching and for other laboratory studies.

Initial examination

The type and magnitude of the injuries can be determined by information gleaned from the initial examination. For example:

A closed -head injury—injury inflicted to the brain without any evidence of scalp laceration

An injury resulting from a high -speed, nonimpact acceleration–deceleration

Blunt trauma with or without a scalp laceration or contusion (all scalp lacerations should be checked manually for an underlying skull fracture)

A penetrating wound from a knife or a bullet (entrance and exit wounds must be sought)

Location of a fracture can be determined by certain signs.

Fractures traversing the base of the skull (basilar fractures) often cause ecchymosis behind the ear (Battle's sign) and may be associated with otorrhea.

Anterior basal fractures often result in periorbital ecchymosis (raccoon's eyes) and subconjunctival hemorrhage and, if associated with cribriform plate fracture, may result in rhinorrhea.

Hematotympanum is associated with fracture of the petrous ridge.

History. After the initial management, and if the patient is awake, a quick history should be obtained.

Severity of head injury and final outcome are directly related to the duration of unconsciousness, which the history may reveal.

Neurologic evaluation. A rapid assessment of the patient is performed.

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The Glasgow Coma Scale (GCS) is now used almost universally in the assessment of the head-injury victim (see Table 21 -2). Motor responses, eye responses, and verbal responses are measured.

The GCS score ranges from 3–15.

The GCS score at 6 hours after trauma is a good predictor of the long-term outcome in head injury (i.e., recovery, disability, vegetative state, or death).

Adult patients with a 6-hour GCS score below 7 are likely to have a poor outcome; the prognosis is much better in the pediatric population.

Coma is defined as GCS score lower than 8.

Neurologic examinations are repeated periodically; a change of 2 or more in the GCS score is considered significant.

Radiographic studies

Computed tomography (CT) scans are preferable to skull radiographs in severely injured patients.

Diagnostic findings

Hematomas (see VII B 1–2) can be easily diagnosed because acute blood appears, relative to the brain:

Hyperdense if hemoglobin >9 mg/dL

Isodense if hemoglobin = 9 mg/dL

Hypodense if hemoglobin <9 mg/dL

Epidural hematomas appear as semilunar (“lenticular”) dense collections with a convexity toward the brain.

Acute SDHs have a concavity toward the brain and conform to the shape of the brain surface.

Cerebral edema can be assessed by the size of the ventricles, basal subarachnoid cisterns, loss of gyral pattern, and degree of midline shift.

If the CT scan is positive, the patient is taken immediately to the operating room for evacuation of hematomas or to the intensive care unit for ICP monitoring and management of brain swelling.

In a patient with significant neurologic deficits, MRI brain scan may show brain injury when a CT head scan result is normal.

Locations of shearing injuries (white matter edema and disruption) are imaged better with MRI scan than CT scan.

Diffuse shearing injuries are frequently located in the corpus callosum, subcortical white matter, thalamus, and brain stem.

Radiographs of the cervical spine are taken to rule out associated spinal injuries.

The presence of cervical spine fracture or neurologic deficit referable to cervical spine is an absolute contraindication for removal of immobilization devices (cervical collar) or performance of flexion/extension views.

Cervical spine series is incomplete until C-1 to T -1 levels are adequately visualized.

In the absence of cervical fracture or cervical spinal cord deficit, flexion/extension views of the cervical spine are required to rule out ligamentous injury.

In the patient who has been comatose for longer than 2 weeks, an MRI of the cervical spine can be useful to perform lateral or flexion/extension views to rule out occult ligamentous injury, disc herniation, or SCI.

D Management of increased ICP

Maintenance of an adequate CPP to prevent irreversible ischemic injury is the major goal of treatment of increased ICP. The patient's CPP is maintained above 50 mm Hg by manipulation of the ICP and the MAP.

Placement of an ICP monitor is necessary to evaluate status and ICP therapy in the unconscious patient.

Criteria for placement of an ICP monitor include one or all of the following:

A GCS score of less than 8. In practical terms, for the intubated, unconscious patient, ICP monitoring is usually needed when the best motor response is decorticate or decerebrate posturing or flaccid.

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Associated systemic complications, such as severe hypotension or hypoxia

CT evidence of diffuse cerebral swelling , especially with obliteration of perimesencephalic cisterns, indicating limited residual compliance and minimal tolerance to further brain swelling

ICP measuring devices (monitors) are of three types:

Intraventricular catheter (ventriculostomy) gives the most accurate measurement and allows removal of CSF to lower the ICP in an emergency. Placement of an intraventricular catheter can be difficult in the presence of diffuse brain swelling with slitlike ventricles.

Subarachnoid bolts (Richmond screw or Philly bolt) are easy to place, give accurate readings, and are associated with a low infection rate.

Intraparenchymal monitors

These devices are fiber -optic ICP probes and are useful when a ventriculostomy catheter cannot be placed.

The intraparenchymal monitor is also useful for superficial cortical monitoring in patients with consumptive coagulopathy, thus reducing risk of hemorrhagic complication of a more deeply placed ICP monitoring probe.

Intracranial hypertension can be managed by a variety of methods. The following therapies can be used in sequence.

Elevation of the patient's head promotes venous drainage, thereby decreasing ICP.

Hyperventilation is used in patients with GCS score greater than 5. The cerebral vessels respond quickly to a change in the arterial Pco2 . A low Pco2 causes vasoconstriction, thus reducing the blood component of the intracranial volume, whereas an elevated Pco 2 causes vasodilation.

The Pco2 is maintained between 22 and 28 mm Hg. Hyperventilation is not a long-term option for ICP control.

If the ICP is not sufficiently lowered by hyperventilation, other therapies have to be used, such as:

Hyperosmolar agents

Loop diuretics

Barbiturates

Increasing the serum osmolality (to approximately 300–310 mOsm)

Hyperosmolar agents

The diuretic most commonly used is mannitol, which is administered intravenously to adults in a bolus of 1.0 g/kg followed by infusion of 25–50 g every 4–6 hours. Its effect can be seen in 5–20 minutes.

A combination of albumin and loop diuretics (furosemide) has been shown in experimental studies to be superior to mannitol for achieving reduction of cerebral edema.

Serum osmolality and electrolytes have to be measured every 6 hours.

Mannitol should be held for serum osmolality greater than 310 mOsm/L, and systolic blood pressure less than 110 mm Hg.

Loop diuretics. Furosemide is the drug most commonly used and is administered intravenously. The effect of the drug is rapid.

Barbiturates may be used if all of the previously mentioned efforts fail to lower the ICP.

An initial dose of 3 mg/kg of sodium pentobarbital is given intravenously, followed by a maintenance dose of 0.5–3 mg/kg/hour. The effect of the drug occurs within minutes. A burst suppression pattern on compressed spectral array electroencephalogram consisting of 3–6

bursts per minute suggests that a therapeutic response has been reached. It is not useful to monitor serum barbiturate levels.

Barbiturates cause myocardial depression and loss of vascular tone, which lead to hypotension, and vasopressor agents may be necessary to elevate the MAP to maintain an adequate CPP.

Although the exact mechanism of action is not known, barbiturates may act by:

Decreasing cerebral blood flow

Reducing the metabolic activity and nutritive demands of the brain

Reducing synaptic transmission

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All patients undergoing barbiturate coma therapy should have a Swan -Ganz catheter placed to measure cardiac pressures and optimize cardiac output.

Hypothermia may be used as an adjunct to other therapies. The core temperature of the body is lowered from normal to a temperature that ranges from 32°C–34¼°C. This method probably decreases the ICP by reducing cerebral metabolism.

Complications of hypothermia include cardiac depression below 32¼°C.

An increased incidence of infectious complications (e.g., pneumonia) has been reported with hypothermia therapy.

Consumptive coagulopathy

Severe parenchymal brain injury causes release of tissue thromboplastin, which activates the extrinsic clotting pathway.

Diffuse intravascular fibrinolysis ensues, completing disseminated intravascular coagulation and fibrinolysis, due to head injury.

The complete clinical syndrome is diagnosed with extended prothrombin time (PT) and activated partial thromboplastin time (APTT) values, decreased fibrinogen level, elevated fibrin split products, and decreased platelet count.

Extended PT and APTT are treated with fresh frozen plasma.

Fibrinogen levels below 150 mg/dL require cryoprecipitate for treatment.

Platelet packs should be given to treat head-injury patients with a platelet count less than 100,000/mL if the bleeding time is extended.

Post -traumatic epilepsy. Risk of post-traumatic epilepsy correlates with severity and location of underlying brain injury. Failure of cerebral perfusion can occur when seizure activity is superimposed on the injured brain.

Patients who are at risk for early post-traumatic epilepsy include those with:

Intracranial hematoma

Supratentorial depressed skull fracture

Brain injury with focal neurologic signs or post-traumatic amnesia for more than 24 hours

Combat missile wounds

Prophylaxis for patients at risk, including those who have experienced more than one seizure due to head injury and patients in the high-risk categories mentioned above, is phenytoin (1.0 g intravenously [not to exceed 50 mg/minute] or by mouth as loading dose, followed by 300 mg per day, or as needed for therapeutic serum level). Dose for children is 10 mg/kg initially, followed by a maintenance of approximately 5 mg/kg per day.

E Management of intracerebral hematomas and cerebral contusions

Intracerebral hematomas result from the tearing of small vessels in the white matter and are due to penetrating trauma or acceleration–deceleration injuries.

Cerebral contusions. Superficial hemorrhages most commonly occur when the anterior temporal and frontal lobes strike the rough edges of the tentorium or skull.

A coup injury occurs when the skull strikes the brain underlying the site of impact.

A contrecoup injury occurs directly opposite to the impact site when the brain strikes the inner table of the skull on the opposite side along the force vector. Thus, if a person were struck on the back of the head, the coup injury would be to the occipital lobe and the frontotemporal tips would sustain the contrecoup injury.

Surgical decompression of intracerebral hematomas and cerebral contusions may be necessary when increased ICP (caused by a mass effect from the accumulated blood and the secondary edema) becomes refractory to medical management.

F Management of scalp injuries

The scalp is made up of five layers:

S ––skin

C––dense subcutaneous tissue

A––aponeurosis

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L ––loose areolar tissue

P ––pericranium

The scalp is highly vascular, and much blood can be lost from scalp lacerations before they are sutured.

The scalp wound is thoroughly cleansed, debrided, and sutured as soon as possible.

Any laceration larger than 6–8 inches should be closed in the operating room.

G Management of skull fractures

Classification

Linear, stellate , or comminuted describe skull fractures, depending on the complexity of the fracture line.

Depressed fractures are those in which a portion of the vault is displaced inward.

Compound fractures are present if the overlying scalp is lacerated.

Basilar fractures traverse the base of the skull.

Operative intervention

Depressed skull fractures may be associated with dural tear and underlying brain damage. Depressed skull fractures larger than 1 cm or the width of the skull in depth are usually surgically elevated.

Epilepsy is due to the immediate neuronal injury that occurs at the time of the depressed skull fracture injury.

Elevation of depressed skull fracture does not affect the incidence of post-traumatic epilepsy.

Compound fractures require a thorough debridement and closure to prevent subsequent infection.

Multiple skull fragments (comminuted) can frequently be reapproximated to reconstruct normal skull contour by use of nylon suture or small plating techniques.

Failure to remove all bone fragments and debride underlying brain of contaminated material (e.g., skin, hair, foreign bodies) may lead to subsequent development of brain abscess.

H Management of CSF

Leaks of CSF, if mixed with blood, can be diagnosed by the ring (halo) sign: If drops of CSF mixed with blood are placed on gauze, a lighter halo forms around a central bloodier area.

Most post -traumatic CSF fistulas close spontaneously with conservative management, which includes elevating the head to reduce both the ICP and the CSF leakage.

Post -traumatic rhinorrhea frequently results from a fracture of the cribriform plate, with associated dural defect.

Post -traumatic otorrhea is associated with fracture of the mastoid air cells and associated dural tear (Fig. 27 -3).

More than 95% of all patients with rhinorrhea or otorrhea due to basal skull fracture and dural tear will resolve with head of bed elevation at 45 degrees.

In some cases, a lumbar CSF drain is placed for continuous CSF drainage to promote fistula healing.

If lumbar drainage fails, craniotomy with closure of the dural defect may be necessary to resolve the leak.

Speed of acceleration or deceleration

Hyperextension versus hyperflexion

Underlying abnormalities in the spinal column secondary to degenerative disease (e.g., disc disease)

The patient's age and associated systemic injuries

D The aims of neurosurgical intervention

Primary focus is on the ABCs of trauma resuscitation (see V C 1 a)

SCI problems include hyperventilation secondary to SCI

Hypotension secondary to neurogenic shock

Additional aims of specific neurosurgical intervention are:

Restoration of bony alignment

Preservation of neuronal function

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E Initial management

Immobilization of the spine in the field before the patient is transferred to the hospital.

An estimated 4%–25% of patients still suffer some improper manipulation of the spine before they arrive at a trauma center.

Patients assumed to have cervical spine injury should be assumed to have more than one focus of spinal injury (i.e., use total spine precautions).

Patients should be in a hard cervical collar and on a spine board.

The use of transfer techniques such as log -rolling and scoop stretchers ensures that full spinal precautions are being maintained.

Stabilization

A patient may have a complete SCI and not feel pain associated with a broken limb or with an internal hemorrhage.

Vital signs and observation of the patient's overall hemodynamic status are very important in SCIs.

Patients with high cervical or high thoracic SCIs may go into neurogenic shock secondary to interruption of the sympathetic pathways.

These patients will develop hypotension in association with bradycardia, secondary to unopposed vagal tone.

Patients often require volume resuscitation and may need pressor agents as well.

Methylprednisolone is now shown in a national cooperative double -blind randomized study to be effective in the treatment of SCI.

Methylprednisolone in high doses should be administered shortly after the diagnosis of an SCI.

It must be administered within 8 hours of the time of SCI to be effective and must be given for 24 hours. Some data suggest that a 48 -hour regimen may be beneficial if treatment is started with more than 8 hours' delay after the initial injury.

Other agents currently under investigation for SCI resuscitation include G M1-gangliosides, glutamate receptor inhibitors, and antioxidants.

Neurologic evaluation

Information obtained from paramedics and emergency medical personnel is important to determine whether the patient ever exhibited motor function.

Motor function must be assessed in all four extremities.

A thorough sensory evaluation needs to be done and a determination made as to whether hemianesthesia exists.

It is important to determine whether hemianesthesia involves the face (not SCI) or just the arms and legs.

The sensory level should be measured, and a determination as to where the sensory level exists should be made rapidly.

The best way to determine a sensory level is to use a sharp pin and mark the level of a pinprick test result.

Reflexes

It is important to make a quick determination of reflexes and to obtain truncal reflexes.

Abdominal reflexes, cremasteric reflexes, and sphincteric reflexes, such as the bulbocavernosus and anal twitch, must also be assessed.

Sacral reflexes are important because of sparing of the sacral segment of the cord. Prognosis for recovery is better if the patient exhibits sacral sparing.

SCIs are classified as complete or incomplete.

Complete SCIs are those injuries with no motor or sensory function below the level of the injury. This is usually a dismal prognosis; 1% of patients exhibit significant recovery if the SCI remains complete for 24 hours.

Incomplete SCIs are important because rapid surgical intervention can help to restore function in these patients. Examples of incomplete SCIs include specific SCI syndromes:

Central cord injury. Results from a concussive blow to the cord. Deficits in the upper extremities are greater than in the lower extremities. Sensory function is usually

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more affected than motor function, and peripheral musculature (e.g., the hands) is usually more severely affected than proximal musculature (e.g., the shoulders).

Anterior SCI usually involves damage to the anterior spinal artery, resulting in infarction or ischemia of the anterior two thirds of the cord. This results in significant muscle weakness. There is a loss of some spinothalamic function; the hallmark is preservation of the posterior column function with intact light touch, position sense, and vibration.

Brown -Séquard syndrome typically occurs from hemisection of the cord, which usually results from penetrating trauma to the spinal cord. The hallmark is ipsilateral loss of motor function, light touch, and vibration with a contralateral loss of pain and temperature.

Radiographic studies. Any patient with an injury above the clavicle should be considered to have a cervical cord injury.

Common practice in the emergency department is to obtain a lateral cervical spinal radiograph as a first assessment of spinal cord alignment. The film must permit evaluation of the C-7/T -1 junction.

Evaluation of the entire cervical, thoracic, and lumbosacral spine may be required.

Any patient with an SCI requires full radiographic assessment (often CT scan) through the area of abnormalities identified in spinal films.

Once bony abnormalities have been identified with plain radiographs and CT scan (Fig. 27 -4), an additional evaluation may be necessary. MRI is increasingly becoming the second study of choice. MRI can reveal intramedullary abnormalities (contusion or intramedullary hematoma) and extra-axial abnormalities (e.g., an epidural hematoma or ruptured intervertebral disc).

In patients with contraindications to MRI (e.g., cardiac pacemaker, prosthetic metal devices), a full myelographic study of the spine may be necessary.

Treatment

Immobilization. The patient should not undergo any undue manipulation of the spine if an SCI is suspected.

FIGURE 27-4 CT scan, axial view, C-5 level. Note the midline fracture through the C-5 body and spinous process base.

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The patient should be immobilized in a hard cervical collar as well as on a rigid spine board until the level of SCI has been fully revealed.

If the patient requires closed reduction, traction is often successful.

In the past, Gardner -Wells tongs were used almost exclusively for traction.

More recently, lighter halo rings have been applied to the patient and used for traction.

Patients who have highly unstable cervical cord injuries or cervical-thoracic cord injuries often will require immobilization in a halo device until definitive reduction can be accomplished.

Open reduction and fixation. In the last two decades, there has been an increasing trend toward aggressive surgical reduction and fixation for unstable vertebral injuries.

Patients who undergo definitive surgical reduction and fixation can be more quickly mobilized and rehabilitated. This is translated into decreased mortality and morbidity from complications secondary to SCI.

Indications for acute surgical intervention. Immediate surgical intervention is required in patients with incomplete SCI and in patients who exhibit progressive neurologic deterioration with myelographic evidence of a block or an MRI scan suggestive of external compression.

For most SCI patients, surgery is required under more subacute conditions. These patients need extensive stabilization in the intensive care unit and then later undergo definitive reduction and fixation.

Epidural hematoma is a collection of blood between the bone and dura, usually of arterial origin, caused by laceration of the middle meningeal artery with an associated fracture of temporal bone. Less common etiologies include bleeding from the middle meningeal vein, venous sinus, or skull diploe.

Diagnosis

Between 10% and 15% of patients present with a lucid interval. That is, the patient is knocked out immediately after injury (concussion effect), then quickly regains consciousness but has a headache, and then slowly loses consciousness (over minutes to hours) again as the epidural hematoma expands and creates mass effect and elevated ICP.

Unenhanced CT has a characteristic appearance of lenticular (or lens -shaped) high density adjacent to bone.

Treatment

Very small epidural hematomas without evidence of significant mass effect and without clinical deficits can be followed up with serial CT scans and close clinical observation. If the hematomas do not expand or produce deficits, then they can be managed conservatively.

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Epidural hematomas that are associated with neurologic deficits or that produce significant mass effect must be evacuated, and the lacerated blood vessel must be identified and ligated.

SDH is a collection of acute or chronic blood that accumulates between the dura and the pia arachnoid.

Usually, SDH is from disrupted bridging veins between the dura and the cortical surface. Often, the blood accumulates very slowly over days or even weeks after a trauma often perceived as trivial, especially in the elderly. Many times, a clot will begin lysing and become enveloped by a membrane of fibrous tissues and delicate capillaries, leading to what is called a chronic SDH.

Diagnosis

Acute SDH presents as an evolving and expanding mass lesion. Often, there is deteriorating mental status with worsening focal deficits.

Chronic SDH is often a subtle, slow, progressive deterioration (e.g., headache, hemiparesis, hemianopsia) over weeks or months, which often presents as dementia, typically in the elderly patient. Chronic SDH is called the “great impersonator” because its clinical manifestations are legion.

CT scan is the diagnostic method of choice.

Acute SDH appears as a hyperdense lesion that shifts and compresses adjacent brain. It is often associated with an underlying contusion. Typically, it is not lenticular shaped; usually, the collection hugs the contour of the adjacent cerebral hemisphere.

Chronic SDH is present bilaterally 50% of the time. It is usually a hypodense or isodense collection associated with shift and compression. Isodense hematomas can be detected with contrast-enhanced CT scan.

Treatment

Acute SDH with decreased mentation or focal neurologic symptoms usually requires craniotomy and surgical evacuation of the dense clot.

Chronic SDH can often be treated initially with burr hole drainage of the lysed, liquefied clot; reaccumulation can require craniotomy for definitive drainage or subdural peritoneal shunt.

SAH may be spontaneous (e.g., aneurysm or arteriovenous malformation). The most common cause of SAH is trauma. Usually, there is a diffuse collection of blood in the subarachnoid space, which is normally filled with CSF and bathes the cerebral vessels.

Spontaneous SAH due to aneurysm rupture is usually associated with sudden onset of severe headache, often associated with nausea, vomiting, stiff neck, photophobia, decreased mentation, and a history of earlier severe so-called herald headaches (i.e., heralding a catastrophic SAH; “sentinel bleed”). Certain types of aneurysms are associated with specific neurologic findings.

Posterior communicating artery aneurysm is associated with third nerve palsy.

Internal carotid–ophthalmic aneurysm is associated with monocular visual field cut.

Diagnosis. CT scan demonstrates nearly 90% of all SAH.

If the CT scan is negative and shows no mass effect, then it is safe to proceed with lumbar puncture to establish diagnosis of SAH.

If CT or lumbar puncture is positive , an angiogram will be needed to determine the following (Fig. 27 -5):

Is there one aneurysm or more than one ? Fifteen percent of patients have multiple aneurysms.

If there are multiple aneurysms, which aneurysm is the one that most likely ruptured? There appears to be a correlation between aneurysm size and risk of rupture.

What is the exact orientation of the aneurysm? How can it be approached surgically ? Does it possess a “clippable” neck?

Is there an abnormality ? Fifteen percent of patients do not exhibit an angiographically identifiable source of SAH.

Common aneurysms. Berry aneurysms can occur at almost any junction point of any artery or any point along a vessel that receives an unusually strong stream of arterial blood. However, there are some very common aneurysms.

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FIGURE 27-5 A: Anterior–posterior cerebral angiogram, right-sided internal carotid artery injection, demonstrating anterior communicating artery aneurysm. B: Oblique image, cerebral angiogram, delineating anterior communicating artery aneurysm.

Internal carotid–posterior communicating artery aneurysm typically presents with third nerve palsy with a dilated ipsilateral pupil.

Anterior communicating aneurysm is occasionally associated with chiasmal compression. Usually, CT scan shows a thick SAH in the frontal interhemispheric fissure.

Internal carotid–ophthalmic artery aneurysm is often bilateral and is more common in female than male patients.

Basilar artery aneurysms are the most frequent posterior circulation aneurysm. They are often associated with multiple cranial nerve deficits and brain stem dysfunction.

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Uncommon aneurysms. There are a variety of other aneurysms besides the berry type. These aneurysms include:

Inflammatory aneurysms , which arise secondary to infection of a cerebral artery (“mycotic aneurysm” technically refers only to fungal infection)

Atherosclerotic aneurysms , which form ectatic or fusiform aneurysms (these seldom hemorrhage but are more likely to make their presence known by pressing on eloquent structures or by leading to thromboembolic infarcts)

C Treatment

Surgical clipping with a small metallic clip placed around the aneurysm neck denies flow to the weakened, dilated dome of the aneurysm and is the standard treatment.

Interventional radiology, the obliteration of the aneurysmal sac by placement of thin metal coils by using angiographic technique, is rapidly gaining ground as the treatment of choice for aneurysms with well-defined necks. The obvious risk of the technique is vessel perforation with catastrophic consequences. However, in experienced hands, the procedure is safe and greatly simplifies patient care.

Some types of aneurysms in the internal carotid artery can be treated with gradual occlusion of the carotid artery in the neck to diminish the flow and induce thrombosis in the aneurysm.

SAH patients require extensive and often complex care in the intensive care unit to address a host of problems, such as hypertension, hyponatremia, cardiac arrhythmias, vasospasm, stroke, and hydrocephalus.

Inflammatory aneurysms frequently resolve with antibiotic or antifungal therapy.

D Prognosis

The rate of bleeding from unruptured aneurysms is 2%–3% per year. Approximately one third of patients die from an SAH before they reach hospital care; another one third die during their acute hospitalization, either from rebleed before definitive clipping or from complications; and one third survive. Of the surviving one third, approximately 50% are able to return to their former lifestyle or line of work. The rest survive with impairment.

VIII Tumors of the Central Nervous System

A Overview

The overall incidence of brain tumors in the United States is approximately 10,000–13,000 new cases per year; 4,000 cases are spinal cord tumors.

CNS tumors are the most common solid tumor encountered among young patients, and they account for approximately 20% of all pediatric neoplasms.

Bimodal distribution for the frequency of brain tumors

First frequency age peak occurs in childhood (3–10 years of age).

Among children, 50% of brain tumors occur in the posterior fossa, and 50% occur in the supratentorial compartment.

Common brain tumors occurring among children are cerebellar astrocytoma, medulloblastoma, craniopharyngioma, and brain stem glioma.

Second frequency peak occurs in the sixth decade.

Most common brain tumors occurring among adults are metastatic carcinoma, malignant glioma, meningioma, and pituitary adenoma.

Incidence of brain tumor according to gender

There are significant genetic issues with respect to brain tumors and sex ratio. Neurofibromatosis types I and II have also been associated with chromosomal abnormalities.

Most brain tumors show a preponderance among males.

Medulloblastomas exhibit a 5:2 male:female ratio.

Meningiomas reveal a 4:1 ratio favoring females over males; meningiomas also have been found to be associated with abnormalities of monosomy of chromosome 22.

B Classification of brain tumors

The nomenclature for brain tumors is often confusing. In general, there has been an increasing trend to classify tumors based on their histologic characteristics. This is broadly based on the cell origin.

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Cells derived from astrocyte cell lines

Glial tumors (gliomas) constitute nearly 50% of brain tumors.

The histology of the tumor is graded by increasing malignancy from low -grade astrocytoma to anaplastic astrocytoma to glioblastoma multiforme.

Glial tumors can include oligodendrogliomas and ependymomas.

Adults tend to get malignant tumors, whereas children are more prone to low -grade, midline astrocytomas in the posterior fossa.

Nonglial cell tumors. Tumors in this group include meningiomas (which arise from arachnoidal cells), schwannomas (which arise from Schwann's cells), medulloblastomas (which arise from primitive neuroectodermal remnants during embryologic development), pituitary tumors (which arise from hormonal cells in the pituitary gland), pineal tumors (which often arise from germ cells), and tumors arising from the blood vessels (e.g., hemangioblastomas and metastatic tumors).

C Diagnosis

Tumors make themselves apparent by symptoms that are related to several mechanisms.

Mass effect

The brain and spinal cord are relatively intolerant of space -occupying lesions, which compete with normal tissue for space within the rigid skull or vertebral canal.

As a general principle, CNS tissues are much more tolerant of slow -growing lesions than of rapid volume change.

Eloquence

Tumors in eloquent areas of the brain become symptomatic while relatively small as opposed to lesions in relatively “silent” areas of the brain, where the tumor becomes symptomatic first when the mass effect is great enough to affect eloquent structures at some distance.

As a general rule, the more eloquent the region in which the lesion arises, the more dramatic the patient's symptoms.

CNS dysfunction can occur because of blood flow impairment. Tumors can impede blood flow by several methods.

Compression of normal blood vessels, depriving normal brain tissue of sufficient blood flow

Tumors can produce brain dysfunction by a “steal phenomenon.” As tumor metabolism increases, blood flow is diverted from normal areas of the brain, causing dysfunction.

Tumors can produce metabolic impairment by growth factors and chemical messengers and interfere with normal “host” brain function.

Tumors can cause seizures, either by direct mechanical irritation or by affecting normal brain metabolism through parts a, b or c above.

Tumors can obstruct CSF outflow, which can lead to gradual enlargement of the ventricles and hydrocephalus.

D Neurologic evaluation

A history of either acute onset or progressive neurologic deficits should be elicited.

The presence of asymmetry upon examination may indicate upper motor neuron dysfunction.

An examination that indicates specific lobar dysfunction is highly suspicious for a focal lesion, such as a brain tumor.

Additional studies are required to pinpoint the lesion. It is important that CT and MRI scans be obtained with contrast to demonstrate disruption of the blood–brain barrier (a frequent manifestation in the vicinity of a tumor). Studies include:

CT scan

MRI scan

Skull films

Angiography

PET scan

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E Specific tumors (supratentorial)

Astrocytomas of the cerebrum are generally slow -growing, infiltrating tumors with poorly defined borders.

Peak incidence is during the fourth decade of life.

Clinical presentation. Astrocytomas often present with seizures, headaches, increased ICP, and focal neurologic deficits. CT and MRI scans show irregular nonhomogenous enhancement with a zone of edema around the tumor.

Treatment includes:

Aggressive surgical resection with an attempt to completely resect the tumor

Radiation therapy

An additional focal radiation boost to the bed of the tumor (with brachytherapy or stereotactic radiosurgery)

Chemotherapy

Prognosis is often related to several factors, including age of the patient, neurologic condition, and histology of the tumor.

Patients with low -grade astrocytomas have a median survival of approximately 5 years.

Patients with anaplastic astrocytomas have a median survival rate of 2 years.

Patients with glioblastomas have a median survival rate of 1 year.

Ependymomas are generally well-circumscribed tumors that occur in the vicinity of ventricles; they often metastasize through CSF pathways.

Clinical presentation often includes increased ICP and symptoms secondary to increased ICP. MRI or CT scan shows an irregularly enhancing lesion with a well-defined border in the vicinity of the ventricle.

Treatment includes:

Aggressive surgical resection

Radiation therapy

Prognosis. The median survival for patients with ependymomas is 5 years.

Oligodendrogliomas are slow -growing gliomas that often have calcification in them.

Clinical presentation. The most common presentation is seizures, and there is often a focal neurologic deficit. CT and MRI scans reveal calcified areas in nearly 40%–50% of tumors.

Treatment includes surgical resection, with or without radiation therapy.

Prognosis. The median survival rate is 10 years for a patient with oligodendrogliomas.

Meningiomas account for 15% of intracranial neoplasms, with a clear predilection for females. Lesions are usually adjacent to the dura with a well-defined border. Meningiomas often have variable amounts of calcium within them and are often associated with extensive edema in the adjacent brain, which is often badly compressed.

Clinical presentation includes headache, focal neurologic deficits, and seizures. CT and MRI scans often reveal homogenous, intensely enhancing mass and well-demarcated border with normal brain.

Treatment includes surgical excision; it can include radiation therapy. New modalities include chemotherapy for malignant meningiomas.

Prognosis is variable, depending on factors such as location and extent of resection.

Metastatic tumors. Approximately one fifth of cancer patients will develop intracranial metastases. Metastases from lung, breast, prostate, kidney, and malignant melanomas represent the most frequent source of intracranial metastases.

Clinical presentation includes increased ICP, obstructive hydrocephalus, focal neurologic deficit, and spontaneous intracerebral hemorrhage. CT and MRI scans often reveal well-circumscribed, enhancing masses surrounded by a ring of cerebral edema. Often, there are multiple lesions typically distributed at the junction of the gray and white matter.

Treatment includes surgical resection if the lesion is solitary or the histology is in question. Treatment also includes steroid and whole -brain radiation therapy followed by focal radiosurgical boost.

Prognosis. Approximately 50% of patients with a single intracranial metastasis will live for 1 year after diagnosis. Survival is increasing with more aggressive therapy, including stereotactic radiosurgery and chemotherapy.

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Meningiocarcinomatosis is a special case of metastatic tumor in which the tumor spreads diffusely throughout the subarachnoid space. Typically, these patients present with evidence of meningismus and ventricular obstruction and may require shunting. Cranial nerves II, VII, and VIII are most commonly involved. Meningiocarcinomatosis is most commonly associated with leukemia, lymphoma, or breast cancer. Often, this type of tumor requires radiation therapy and intrathecal chemotherapy.

F Specific tumors (infratentorial)

Posterior fossa tumors. Approximately 50% of brain tumors in children are located in the posterior fossa. By contrast, only 25% of tumors in adults are in the posterior fossa.

Types. These tumors include midline cystic cerebellar astrocytomas of the cerebellum and brain stem, medulloblastomas, ependymomas, choroid -plexus papillomas, and epidermoid tumors. Most common are acoustic neuromas, epidermoid cysts, meningiomas, and hemangioblastomas.

Clinical presentation. Tumors of the posterior fossa can present with a headache secondary to ventricular obstruction. They can also present with ipsilateral ataxia and lack of coordination from lesions in the cerebellum as well as unsteady gait and truncal ataxia. In addition, loss of equilibrium and nystagmus may be present.

Treatment and prognosis depend on tumor type and location.

Medulloblastomas are malignant tumors of the vermis and the fourth ventricle from arrest of neuroectodermal cells during embryologic development. These tumors are most frequently encountered during the first and second decades of life, with a male predominance.

Clinical presentation. These tumors most commonly occur in the midline or lateral cerebellar hemisphere. Patients with a medulloblastoma present with cerebellar and brain stem dysfunction and increased ICP. CT and MRI scans demonstrate a nonhomogenous, enhancing mass usually adjacent to or in the fourth ventricle.

Treatment is extensive surgical resection and radiation therapy to the site as well as the rest of the entire neuraxis to prevent CSF seeding. Radiation therapy cannot always be used in young children, and chemotherapy remains the treatment of choice after surgery.

Prognosis. Thirty-three percent of patients survive 10 years. Survival is increased by total resection and radiation therapy.

Ependymomas arise from the floor of the fourth ventricle and are most common during childhood.

Clinical presentation. Ependymomas usually present with obstruction of CSF pathways. There is increased ICP and disequilibrium. CT and MRI scans show a modular, multilobulated, enhancing tumor in the fourth ventricle.

Treatment. Ependymomas are surgically resected, but often the floor of the fourth ventricle cannot be invaded to remove the tumor. Radiation therapy is usually required after removal.

Prognosis. Median survival for patients with an ependymoma is 2.5 years.

Brain stem gliomas. These tumors occur most frequently in the first decade of life.

Clinical presentation

Typically, this tumor presents with cranial palsies of the brain stem with gait unsteadiness and evolving myelopathy.

Hydrocephalus can occur secondary to fourth ventricular obstruction.

CT and MRI scans often demonstrate diffuse and poor enhancement of an intra -axial lesion within the brain stem.

Classic MRI appearance is sufficient for diagnosis, obviating the need for biopsy.

Treatment. Tumors are often largely unresectable. Radiation therapy remains the mainstay of treatment.

Prognosis. Median survival for a child with a brain stem glioma is 2 years.

Cerebellar astrocytomas have a much more benign history than astrocytomas occurring elsewhere. Like brain stem gliomas, their peak incidence is in the first decade of life, but they are generally restricted to the cerebellum. Cerebellar astrocytomas are often cystic.

Clinical presentation. Patients typically present with cerebellar dysfunction and ipsilateral dysmetria. With progressive growth, obstructive hydrocephalus can develop. CT and MRI

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scans usually reveal a multicystic or cyst -associated enhancing nodule. The nodule may be low density and is often located in the lateral cerebellar hemisphere.

Treatment and prognosis. Tumors can be completely resected in up to 80%–90% of patients, which usually results in cure. Even patients who undergo partial resections have a median survival of 8 years.

Hemangioblastomas are the most common primary intra -axial tumor in the posterior fossa in adults.

Clinical presentation. Patients present with cerebellar dysfunction.

Hemangioblastomas can be a part of von Hippel–Lindau disease with hemangioblastomas of the cerebellum and retina, in association with congenital cysts of the kidneys, pancreas, liver, and renal cell carcinoma. Approximately 10% of these patients have erythrocytosis secondary to tumor secretion of erythropoietin.

CT and MRI scans usually reveal a mural nodule within a cyst; the nodule is intensely enhancing.

Angiography reveals an intense vascular blush on this lesion.

Treatment. Surgical resection is the treatment of choice but may be extremely difficult due to the vascularity of the tumor.

Tumors of the cerebellopontile angle. Typically, these tumors involve the cerebellopontile angle with differential involvement of cranial nerves V, VII, and VIII as well as the adjacent cerebellum. Several tumors may be involved in this location, including acoustic neuromas, meningiomas, and epidermoid cysts.

Acoustic neuromas arise from the vestibular portion of cranial nerve VIII.

Clinical presentation. These are benign tumors that usually present with tinnitus, hearing loss, and evolving unsteadiness. Commonly, the patient first notices problems with speech discrimination followed by a gradual loss of hearing. With large tumors, there is often loss of the corneal reflex as well as facial weakness. If the tumor is quite large, it compresses the cerebellum and leads to nystagmus and gait ataxia.

Enhanced CT and MRI scans often demonstrate acoustic neuroma in the internal auditory meatus. Often, the internal auditory meatus is expanded or trumpet-shaped from the lesion.

MRI has now become the method of choice for evaluating the posterior fossa and cerebellopontile angle because these structures are better seen on MRI. With CT, bony artifacts from the petrous ridge often hide important radiographic features.

Brain stem auditory evoked potentials and audiometric testing are very useful for lesions affecting the VIII nerve or a brain stem.

Treatment involves resection or stereotactic radiosurgery.

Prognosis is related to tumor size and extent of resection.

Meningiomas may also present in the cerebellopontile angle with precisely the same signs and symptoms as acoustic neuroma.

Epidermoid cysts also commonly occur in the cerebellopontile angle and again can present with cerebellopontile angle syndrome. Progressive dysfunction of cranial nerves V, VII, VIII, and the lower cranial nerves, along with progressive cerebellar compression, are typical.

G Pituitary tumors

Clinical presentation. Pituitary tumors tend to present in one of three ways.

The first way is with headache and compression of the optic chiasm. Frequently, the patient presents with bitemporal hemianopsia.

The second presentation is with endocrinopathy. Often, endocrinopathies consist of Cushing's syndrome (secondary to excess adrenocorticotropic hormone secretion), acromegaly (secondary to excessive growth hormone secretion), hyperprolactinema, or hypopituitarism.

The third presentation is the occasional presentation of a tumor with pituitary apoplexy. This is an acute massive hemorrhage into a pituitary tumor, which may mimic the onset of a ruptured berry aneurysm. Frequently, these patients will have headache, impaired vision, extraocular muscle dysfunction, stiff neck, and endocrinopathy.

In approximately 30% of the cases, the patients do not have endocrinopathy (so-called nonsecreting pituitary adenomas).

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Diagnostic tests

Radioimmunoassays are used to document the level of specific hormones in situations of endocrinopathy.

CT and MRI scans are useful for demonstrating the erosion of the sella as well as sellar and suprasellar tumors.

Angiography is still occasionally used in the event that there is some question about whether an intrasellar or suprasellar aneurysm may be present.

MRI with and without contrast has now become the method of choice for diagnosis. With modern MRI techniques, flow voids associated with aneurysms are usually detectable.

Treatment

Medical therapy in the form of bromocriptine (a dopaminergic agonist) can often be used successfully for prolactin -secreting adenomas. Bromocriptine has also proved useful for other kinds of endocrinopathies, such as in some selected patients with acromegaly.

Surgical resection is the treatment of choice for most nonprolactin -secreting tumors and prolactinomas that are progressively symptomatic despite medical therapy. This is especially true for tumors that are impinging on the optic chiasm.

A trans-sphenoidal route can be used for small tumors with little suprasellar extension.

For tumors with extensive suprasellar mass, a frontal or pterional craniotomy may be required.

Radiation therapy (usually in the range of 4,000–5,000 Cgy) is frequently used as an adjunct after partial surgical resection and is effective in controlling approximately 90% of pituitary adenomas that remain after surgery.

IX Congenital Lesions of the Nervous System

A Dysraphism

Usually, defective fusion of a raphe is associated with some findings on general physical examination. For example, examination of the back may reveal a tuft of hair, a nevus, a lipoma, abnormal blood vessels, a dimple, or a sinus tract. All of these are highly suggestive of an underlying dysraphic state.

Spina bifida results from failure of fusion of the vertebral arches.

It may be totally asymptomatic and be found incidentally on spinal radiograph (spina bifida occulta), or it may be symptomatic.

Spina bifida can be associated with other congenital anomalies, such as dermal sinus, diastematomyelia (splitting of the cord into halves), or neuroenteric cysts.

Meningocele. This rare lesion is a saclike posterior midline herniation of the dura mater and is usually not associated with any neurologic deficits. Repair is indicated primarily for cosmetic reasons.

Myelomeningocele is herniation of the dura mater and neural elements posteriorly as a result of incomplete closure of the spine. This lesion may be associated with hydrocephalus secondary to a Chiari malformation (i.e., an abnormally low position of the cerebellar tonsils).

Surgical treatment is aimed at closure of the defect.

Neurologic defects are common, and their severity is related to the location of the lesion. Patients with high lesions have a worse prognosis.

B

Hydrocephalus literally means “water head,” and the abnormality may be congenital or acquired. It is caused by an obstruction to the flow (obstructive hydrocephalus) or reabsorption (communicating hydrocephalus) of CSF.

Etiology. The most common causes are:

Sequelae of intraventricular hemorrhage in the premature baby

Aqueductal stenosis

Chiari malformation

Type I. The fourth ventricle is above the foramen magnum, but the upper part of the cervical cord is displaced caudally.

Type II (most commonly seen). There is a downward herniation of the fourth ventricle and the cerebellar tonsils.

Types III and IV. There is progressive caudal displacement of the cerebellar vermis, pons, and medulla below the foramen magnum.

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Dandy-Walker syndrome , in which there is probable agenesis of the foramina of Magendie and Luschka, resulting in the filling of the posterior fossa with a large cyst and enlargement of the lateral and third ventricles

Clinical findings. Patients may present with bulging fontanelles, scalp vein dilatation, a rapidly increasing head circumference, decreased upward gaze (Parinaud's syndrome), papilledema, lethargy, irritability, nausea, ataxia, and vomiting.

Treatment. A CT or MRI scan is done to confirm the diagnosis, and then a shunt is placed to divert the ventricular fluid.

A ventriculoperitoneal shunt is most commonly used.

In very small infants , the absorptive surface of the peritoneum may be inadequate, warranting the placement of a ventriculoatrial shunt.

CSF may need to be shunted to the pleural space.

X Herniated Disc Syndrome

A Overview

Intervertebral discs contain a soft fibrous center, known as the nucleus pulposus.

The tough fibrous covering is called the anulus fibrosis or disc capsule.

Herniated or “slipped” discs occur when the nucleus pulposus herniates through a rupture or rent in the capsule.

A fragment may extrude completely, in which case it is referred to as a free fragment.

A herniated disc fragment may maintain its continuity with remnants of the nucleus pulposus.

Typically, the disc herniates either underneath or through the posterior longitudinal ligament. It can then come to rest either on the thecal sac, spinal cord, or, more commonly, the nerve roots.

Typically, if the fragment is resting against the nerve root, it produces a recognizable radiculopathic syndrome.

B Cervical disc syndromes

Clinical presentation. Typically, cervical disc herniation presents initially as neck pain, which is presumably secondary to inflammation of the disc capsule and the adjacent posterior longitudinal ligament.

Pain may be located between the scapula, then radiate up into the neck and head.

Radicular signs and symptoms often accompany cervical disc herniation, or they develop during the subacute period.

Symptoms include pain that radiates into the arm, often in a typical distribution.

Cervical disc herniation may be associated with numbness or a dysesthetic pain and weakness as well as loss of reflexes.

The most common disc herniations are the C-6/C-7 disc herniation and the C-5/C-6 disc herniation.

The patient may have cervical muscle spasm.

The pain may be exacerbated by flexion/extension of the neck or lateral rotation as well as by pressing on the vertex of the head.

The disc findings are reviewed in Table 27 -1.

Treatment. Patients are often treated with a conservative regimen of analgesics, nonsteroidal anti - inflammatory drugs, mild muscle relaxants, bed rest, cervical collar, and cervical traction. If conservative therapy is unsuccessful, surgical removal and decompression may be required.

Central and lateral herniation. An anterior approach is used for removal of the disc and

Clinical presentation. Typically, patients have a history of back pain often brought on by trauma, such as lifting or Valsalva's maneuver. Patients often report pain exacerbated by sitting or procedures involving Valsalva's maneuver (e.g., straining or bowel movements).

Physical examination often shows intense lumbosacral spasm. Frequently, a positive “straight leg raising” sign, as well as radicular signs and symptoms, are present. An overview of the physical signs is reviewed in Table 27 -2.

Treatment. As with cervical spine problems, patients are first treated with bed rest, analgesics, antispasmodic agents, and nonsteroidal anti -inflammatory drugs.

If pain does not subside, then patients undergo further study, which can include a CT scan, an MRI scan, or a myelogram (increasingly, MRI is becoming the screening study of choice for disc herniations).

Typically, if the pain is unresponsive to conservative management and bed rest, then the patient will need a discectomy through a posterior approach.

E Lumbar spondylosis

As in the neck, osteoarthritis can produce arthropathy and narrowing of the canal.

Clinical presentation. The patient describes pain that is aching in nature, exacerbated by prolonged standing or walking, and ameliorated by sitting. Most often, the patient reports pain that radiates into the buttocks and down into one or both legs.

Diagnosis. This condition is usually best assessed with plain films and CT scan because it is critical to see the structures of the bones in this particular syndrome. Myelogram may be necessary in some situations to get a better assessment of exactly which nerve roots are being compressed.

Treatment. Conservative therapy, including heat, analgesics, and antispasmodics, may be helpful in some cases. As the disease progresses, surgical decompression by laminectomy may be required.

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TABLE 27-2 Lumbar Disc Herniation Syndrome

Adapted from Freedman AH, Wilkins RH. Neurosurgical Management for the House Officer. Baltimore: Williams & Wilkins; 1984.

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XI Tumors of the Spinal Cord

A Classification

Tumors of the spinal cord are generally classified as being intramedullary, extramedullary, intradural, or extradural. This is based on characteristic myelographic appearances. This classification is still used for both CTand MR-based studies.

B Types

Common tumors of the spinal cord include astrocytomas, ependymomas, schwannomas, neurofibromas, meningiomas, metastases, chordomas, and lipomas.

Astrocytomas. As in the brain, astrocytomas of all grades can occur in the spinal cord. Most frequently, they occur in the cervical and thoracic regions. These tumors may or may not be associated with an intramedullary cyst.

Ependymomas often occur in the cervical spine and are often associated with the syrinx. A second group of ependymomas involves the filum terminale of the lumbosacral region. In general, ependymomas tend to have their peak incidence in the first and second decades of life.

Schwannomas arise from the Schwann's cells, which are associated with the spinal nerve roots. Typically, these present as dumbbell-shaped tumors protruding throughout the neural foramen. They tend to present in the third to sixth decades of life, with radiculopathy that evolves to spinal cord compression. Often, schwannomas may be multiple as part of neurofibromatosis.

Neurofibromas have their peak frequency in the third to fifth decades of life. Their clinical presentation is nearly identical to that of schwannomas and can also be associated with neurofibromatosis.

Meningiomas most typically occur in the thoracic or, less frequently, in the cervical region. They arise in the intradural extramedullary space. As with meningiomas of the brain, they occur predominantly in females.

Metastatic tumors typically occur in the vertebral body, secondary to blood supply to this region. The most frequent primary tumors occur in the lung, breast, or prostate. These tumors tend to occur extradurally and produce extramedullary compression. In contrast, some CNS tumors produce drop metastases, where the primary lesion then spreads to the subarachnoid space in the lumbosacral region. Tumors that have a propensity to do this are medulloblastomas, ependymomas, and pineal tumors that have metastasized throughout the spinal subarachnoid space.

Chordomas originate from remnants of the notochord during embryologic development. Spinal chordomas tend to be in the sacral coccygeal region or in the clival region. These lesions are destructive to bone, and it often is very difficult to get complete resections. Intense radiation treatment is often required after resection.

Lipomas can occur in intradural or extradural locations. Intradural lipomas are usually dorsal to the lumbosacral spine and often are associated with lipomeningocele and tethering of the spinal cord with a lipoma in the filum terminale.

Intramedullary lesions typically present with a gradual evolving myelopathy and often with a partial Brown -

Séquard syndrome. In contrast, extradural lesions often are associated first with a radiculopathy and then with gradual spinal cord compression and myelopathy.

C

Diagnosis is usually established by localizing the level of lesion by neurologic examination and then proceeding with radiographic studies. These studies can include CT or MRI scans with and without gadolinium. MRI is now becoming the study of choice as a relatively quick and noninvasive way to assess the spinal canal as well as the spinal cord nerve roots. In the event that MRI is nondiagnostic, the decision can be made to proceed with standard myelography with or without a postcontrast CT scan.

D Treatment

involves the administration of high-dose steroids to help with spinal cord compression and edema. Surgical intervention is aimed at obtaining tissue diagnosis as well as decompression and stabilization. Often, with incomplete resections of metastatic tumor, radiation therapy is helpful not only in controlling the tumor but also in palliation for pain.

P.528

XII Brachial Plexus Injuries

A Brachial plexopathy

Anatomy. The brachial plexus (Fig. 27 -6) is an exceedingly complex anatomical structure that involves a transition from the cervical roots (C-5/T -1) to the axilla and four main nerves:

Musculocutaneous

Axillary

Median

Ulnar

Clinical presentation. Brachial plexus injuries can occur as a result of blunt, penetrating, or neoplastic injury. Most typically, brachial plexopathy is seen in the setting of trauma where the neck is severely stretched and there is a stretch avulsion injury to the brachial plexus.

Physical examination. Examination of the brachial plexus is complex because it involves not only an evaluation of the cervical cord but also an appreciation of the different motor groups and sensory areas subserved by the different nerves. In general, weakening of the scapula and weakness of the rhomboids are looked for, as is evidence of paralysis or elevation of the ipsilateral diaphragm (injury to the C-4 nerve root or phrenic nerve) or presence of Horner's syndrome.

Evaluation includes extensive electromyography as well as nerve conduction studies. Evaluation of the brachial plexus can involve a myelogram followed by a CT scan with metrizamide or, alternatively, an MRI to evaluate the nerve roots and brachial plexus.

Treatment and prognosis. Nerve root avulsions generally have a very poor prognosis. If there is residual motor and sensory function, then the patient has an excellent chance of regaining function of the nerve root. However, if the nerve root is severed, then the patient may need a cable graft to restore function in these areas.

B

Thoracic outlet syndrome results from occlusion of the subclavian artery or vein. Thoracic outlet syndrome usually results as an aching pain in the axilla or along the forearm that is positionally dependent. If the syndrome is allowed to progress or goes undiagnosed, then weakness can occur, primarily in the intrinsic muscles of the hand. Frequently, a supraclavian bruit is heard on physical examination. Treatment involves resection of an anomalous cervical rib.

FIGURE 27-6 Simplified diagram of the brachial plexus.