High-resolution computed tomography in extrinsic allergic alveolitis

Seventeen patients with extrinsic allergic alveolitis were examined with high-resolution computed tomography (CT). Increased attenuation of the lung parenchyma was present in eleven cases; the corresponding abnormality on chest radiography of ground-glass opacification was found in only five cases. The apparent upper zone sparing on chest radiography was not confirmed on CT which demonstrated a global increase in lung density. Several other abnormalities identified on CT in the subacute phase of extrinsic allergic alveolitis are described and correlated with chest radiographs. Whilst there is no single pathognomonic CT feature of extrinsic allergic alveolitis, there is a characteristic constellation of abnormalities which provide support for an otherwise uncertain clinical diagnosis.