Acute interstitial pneumonia

Histologic features--Acute interstitial pneumonia (AIP) was previously known as Hamman-Rich syndrome.^{41, 42} Pathologically, AIP is characterized by diffuse alveolar damage with hyaline membrane formation and alveolar wall edema during the acute, exudative phase (up to day 6). Later, fibroblast proliferation supervenes in the subacute proliferative phase (day 4 to 10).⁴² Vascular thrombosis may also occur. Finally, after day 8, the chronic, fibrotic phase characterized by traction bronchiectasis and fibrosis may occur.⁴³

Clinical findings--AIP is characterized by the abrupt onset of respiratory failure requiring mechanical ventilation in a previously healthy individual.^{2, 43} Antecedent histories variously include cough, fever, and shortness of breath. AIP may be thought of as ARDS without a known cause.² The mortality is high (60% to 100%), and significant parenchymal opacities on chest radiography and CT may occur in survivors.^{2, 44}

Radiographic findings--Chest radiographs: Findings on plain radiographs include bilateral, symmetric ground glass opacities and foci of air space consolidation (figure 5 -- 27KB). In some patients, subpleural reticulation and honeycomb lung may occur.^{2, 10, 45}

HRCT: The findings of AIP on HRCT have been described^{2, 10, 45, 46} and correlated with the pathologic stage of disease.⁴² Predictably, bilateral, roughly symmetric areas of ground glass opacity and air space consolidation are encountered, often associated with interlobular septal thickening (figure 6 -- 54KB). Traction bronchiectasis and architectural distortion may be seen, particularly in the proliferative subacute and chronic fibrotic phase. AIP is characterized by its rapid time course.⁴⁶

Next page: Alveolar macrophage pneumonia (AMP), previously known as desquamative interstitial pneumonia (DIP) and respiratory bronchiolitis-interstitial lung disease (RB-ILD)

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