CT–Pathology Comparisons

At histologic examination, centrilobular small nodules correspond to cellular bronchiolitis, non-caseating granulomas, and bronchiolocentric interstitial pneumonitis [27] (Fig. 21.3). The lobular areas of mosaic attenuation and air trapping are presumed to be secondary to small airway obstruction due to cellular bronchiolitis or, less commonly, constrictive bronchiolitis. Thin-walled cysts are presumed to result from bronchiolitis and bronchiolar obstruction.

Patient Prognosis

Early diagnosis and avoidance of antigen exposure are crucial in the management. Corticosteroids are recommended in severe respiratory impairment with hypoxemia. If the diagnosis is correctly and timely done, outcome is usually good.

Cytomegalovirus Pneumonia

Pathology and Pathogenesis

CMV pneumonia shows features of interstitial pneumonitis, and some of the alveolar epithelial cells are enlarged and contain characteristic inclusions. These measure up to as much as 10 μm in diameter and are surrounded by a clear zone inside the nuclear membrane. These Cowdry type A intranuclear inclusions have been likened to an owlÕs eyes. The inclusions represent clumped chromatin and the clear zone the virus. Cytoplasmic inclusions up to 2 μm in diameter are often also present. Severe cases may show a necrotizingpneumoniaortracheobronchitis.Immunocytochemistry or in situ hybridization may be useful in cases that the inclusions being well not developed. Diffuse alveolar damage is a further pattern of disease that is occasionally seen in CMV pneumonia [28] (Fig. 21.4).

Symptoms and Signs

Clinical manifestations of CMV pneumonia may range from mild dyspnea to severe respiratory insufÞciency [29]. Most patients present with fever, cough, hypoxia, and dyspnea.

CT Findings

On high-resolution CT, bilateral parenchymal abnormalities consisting of consolidation, GGO, and nodules less than 10 mm in size are the most common Þndings [19] (Fig. 21.4). GGO have patchy or diffuse distribution without zonal predominance. Nodules tend to be bilateral and symmetric and

to have a centrilobular distribution and are sometimes associated with a halo of GGO [18] (Fig. 21.4). Airspace consolidation usually has a lobular or subsegmental distribution. Other Þndings include thickening of bronchovascular bundles and tree-in-bud patterns.

CT–Pathology Comparisons

Patchy or diffuse areas of GGO histopathologically correspond to areas of diffuse alveolar damage. Poorly deÞned nodules or nodules with an associated halo represent focal areas of inßammation or hemorrhage [19] (Fig. 21.4).

Patient Prognosis

Antiviral therapy with ganciclovir with or without hyperimmune globulin enriched for CMV antibodies or foscarnet is effective, but it has a high mortality especially in bone marrow transplantation recipients.

Diffuse Alveolar Hemorrhage

Pathology and Pathogenesis

Whatever the etiology, biopsy shows a combination of alveolar hemorrhage and hemosiderosis. The cause of the hemorrhage is often not evident histologically but there may be intense neutrophil inÞltration of the alveolar walls representing capillaritis and rare cases show diffuse alveolar damage [30].

Symptoms and Signs

Patients with DAH present with cough, dyspnea, and hemoptysis [22]. In fact, one-third of patients will not have hemoptysis, despite active intra-alveolar bleeding. Fever and other systemic symptoms may be present, depending on the etiology of the diffuse alveolar hemorrhage. Careful attention should be given to the nasal and oropharyngeal examination to exclude clues to a vasculitis.

CT Findings

The most common CT features of DAH are bilateral GGO and consolidation [20]. The lesions are diffuse in the upper and lower lobes in approximately three-fourths of patients or are localized in the lower part of the lungs in 25 % of patients. Typically, the halo sign may be seen with parenchymal nodules or masses and consolidation on CT scans (Fig. 21.5).