29  Imaging Approach to Interstitial Lung Disease	513

Alternative Diagnosis

An alternative diagnosis is reached when brosis is observed on a CT but features suggesting a non-idiopathic cause are also present. These primarily include an atypical distribution of disease, predominant ground glass opacities and low attenuation lobules (both occurring on background

normal lung), the presence of cysts, nodules, and consolidation. However, care should also be taken to search out signs suggestive of an underlying connective tissue disease such as a dilated oesophagus (systemic sclerosis; Fig. 29.8a–c) or distal clavicular erosions (rheumatoid arthritis) as well as pleural plaques, effusions and pleural thickening (Fig. 29.8d–f).

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Fig. 29.7  Axial computed tomography images in the upper (a + d), middle (b + e), and lower (c + f) regions of the lungs demonstrate the two scenarios that can give rise to an indeterminate usual interstitial pneumonia (UIP) pattern. The presence of reticulation in a predominantly basal, peripheral and subpleural distribution (a–c) with no evidence of honeycombing or traction bronchiectasis on the scan can result

in a pattern indeterminate for UIP. Alternatively, despite the presence of honeycombing or traction bronchiectasis the distribution of disease throughout the lung may not be typical for idiopathic pulmonarybrosis-­related usual interstitial pneumonia (basal predominant). In this case (d–f) brosis with traction bronchiectasis and reticulation appears evenly distributed throughout all zones of the lungs

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Fig. 29.8  Axial computed tomography images in two patients with connective tissue disease-related lung brosis. A patient with lower zone predominant brosis characterised by traction bronchiectasis has a dilated oesophagus throughout the length of the mediastinum (a–c) suggesting a diagnosis of systemic sclerosis. In a second patient with

rheumatoid arthritis-related brosis (d–f) parenchymal bands are visible originating from the lung periphery in the midzones in keeping with an old exudative pleural effusion. In the lower zones, there is evidence of pleural effusion on the right (arrow)

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