Ground-Glass Opacity without Reticulation, Diffuse Distribution

Smooth interlobular septal thickening becomes superimposed on areas of GGO (a crazy-paving appearance) within 2Ð3 days. These Þndings may show improvement in the course of hemorrhage resorption. Ill-deÞned centrilobular small nodules have been reported to be uniform in size (1Ð3 mm in diameter) and are diffusely distributed with no zonal predominance.

ßuid, cells, or Þbrosis), partial collapse of alveoli, or increased capillary blood volume. Without reticulation, the GGO areas usually represent active inßammatory or reversible disease state (repetition see section ÒGround-Glass Opacity without Reticulation, Subpleural and Patchy DistributionÓ) (Figs. 21.6, 21.7, and 21.8).

CT–Pathology Comparisons

Areas of GGO and consolidation histopathologically correlate with pulmonary hemorrhage, both with or without capillaritis [31]. Ill-deÞned centrilobular small nodules reßect intra-alveolar accumulation of pulmonary macrophages [32].

Diseases Causing the Pattern

Diffuse GGO lesions may be observed in acute hypersensitivity pneumonitis (HP) (Fig. 21.6), Pneumocystis jiroveci pneumonia (PJP), cytomegalovirus pneumonia (CMV pneumonia), pulmonary edema, diffuse alveolar hemorrhage (DAH), acute interstitial pneumonia (AIP), and acute eosinophilic pneumonia (AEP) (Figs. 21.7 and 21.8).

Patient Prognosis

The treatment of DAH depends on the underlying cause of hemorrhage. Corticosteroids are a mainstay of therapy in most cases. Cyclophosphamide or azathioprine may be added. Plasmapheresis may be tried in the cases of the immune etiology. Mortality is considerable especially in small vessel vasculitis.

Distribution

Although diffuse in distribution, subpleural lungs including apices and costophrenic angles may be spared in pulmonary edema and DAH. In PJP, the parenchymal lesions may commence in the infrahilar regions and extend to the peripheral lungs.

Ground-Glass Opacity without Reticulation, Diffuse Distribution

Definition

Ground-glass opacity (GGO) is caused by partial displacement of air in lung parenchyma. The opacity is caused by partial Þlling of airspaces, interstitial thickening (due to

a

Clinical Considerations

In the acute stage ± of HP after direct exposure to the antigen, there is fever, chills, nonproductive cough, dyspnea, malaise, and myalgia, all resembling inßuenza. Exposure to known offending allergens lead to acute symptoms within 4Ð8 h after the exposure and positive precipitating antibodies to the offending antigen [33]. PJP is the most

b

Fig. 21.6 Acute hypersensitivity pneumonitis in a 53-year-old farmer man. (a, b) Lung window images of CT scans (1.5-mm section thickness) obtained at levels of right upper lobar bronchus (a) and liver dome

(b), respectively, show diffuse ground-glass opacity in both lungs. Also note poorly formed centrilobular nodules (arrows)

Fig. 21.7 Acute eosinophilic pneumonia in a 45-year-old man. Patient complains of fever, cough, and dyspnea. (a) Lung window of CT scan (5.0-mm section thickness) obtained at level of bronchus intermedius shows diffuse ground-glass opacity in both lungs. Some areas of consolidation are seen in dependent portion of lungs. Also note smooth interlobular septal thickening (arrows). (b) Low-magniÞcation (×40) photomicrograph demonstrates areas of acute eosinophilic pneumonia

and associated diffuse alveolar damage of proliferative stage and organizing pneumonia pattern (arrows). Please note other area (open arrows) of different stage of diffuse alveolar damage (open arrows, early exudative stage). (c) High-magniÞcation (×200) photomicrograph discloses characteristic eosinophilic aggregates (arrows) in alveolar spaces along with interstitial Þbroblastic thickening due to acute lung damage

common opportunistic infection among persons with AIDS in the United States. The incidence of PJP in solid organ and hematopoietic stem cell transplant recipients remains low because of widespread chemoprophylaxis. Most trans- plant-related PJP infections occur in the early posttransplant period [34]. CMV pneumonia occurs most commonly after bone marrow and solid organ transplantation and in patients with AIDS [19]. The most common underlying histology of DAH is of a small vessel vasculitis known as pulmonary capillaritis, usually seen with seropositive systemic vasculitides, or a connective tissue disorder (bland pulmonary hemorrhage), and diffuse alveolar damage due

to a number of injuries including, drugs, coagulation disorders, and infection [22]. AIP is a fulminant disease of unknown etiology that usually occurs in a previously healthy person and produces histologic Þndings of diffuse alveolar damage. The patients present with symptoms of acute respiratory failure and require mechanical ventilation within 1Ð2 weeks of symptom onset. AEP is characterized clinically by acute febrile illness, severe hypoxemia, diffuse pulmonary opacity, increased eosinophil counts in bronchoalveolar lavage ßuid, no infectious or atopic illness, rapid improvement with steroid therapy, and no relapse [35, 36].