Rounded atelectasis in chronic inflammatory pleural effusion

VRU 2023 - 64(3) 420-428

December 01, 2023

Background: Rounded atelectasis is a condition of lung collapse caused by chronic pleural effusions and inflammation. It can mimic pulmonary neoplasia on CT images and requires cytological or histological confirmation.

Study: The authors describe the CT features of rounded atelectasis in 11 cats and dogs with chylothorax or pyothorax and restrictive pleuritis, and compare them with the human literature.

Methods: The authors retrospectively selected cases that had thoracic CT scans and cytological or histological analysis of the pulmonary nodules. They evaluated the shape, location, contrast enhancement, and other characteristics of the nodules, as well as the presence of comet tail signs and acute angles with the pleura.

Results: The authors found that most of the nodules (92%) had the typical features of rounded atelectasis described in humans, such as round or ovoid shape, peripheral location, acute angle with the pleura, and comet tail signs. None of the nodules had evidence of malignancy or infection on cytology or histology.

Limitations: The study had a small sample size, a retrospective design, and a low number of histological evaluations. Some nodules were not sampled or followed up, and some patients had multiple nodules with different features.

Conclusions: The authors suggest that rounded atelectasis should be considered as a differential diagnosis for pulmonary nodules in cats and dogs with restrictive pleuritis and chylothorax or pyothorax. They recommend using the CT criteria from human medicine to differentiate rounded atelectasis from neoplasia, and to confirm the diagnosis with cytology or histology.

Pre-contrast thoracic CT transverse (A, C) and multiplanar reconstructions (MPR) parasagittal (B, D, E) images in a lung algorithm in dogs (A, C) and cats (B, D, E) diagnosed with chylothorax and restrictive pleuritis. Perilesional tortuous bronchi and vessels coalescing to the pulmonary nodular lesions (comet tail signs) are present (yellow arrows on images B, C, E). The pulmonary nodular lesions additionally create an acute angle with the abutting visceral pleura, depicted by the discontinuous yellow lines on image A. Rounding of the lung margins and a moderate pneumothorax (B, D) can also be identified

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