Diagnostic imaging and histopathologic features of rounded atelectasis in four cats and one dog: A descriptive case series study

Shoko Fukuda, Jennifer A. Reetz, Kohei Hamamoto, Lynn Griffin, Paula A. Schaffer

Background: This paper describes a rare condition called rounded atelectasis in four cats and one dog. Rounded atelectasis is a form of lung collapse that appears as a mass-like lesion on imaging, and can be confused with lung cancer. The authors aim to raise awareness of this benign diagnosis and its imaging features in veterinary species.

Study: The authors conducted a retrospective, multi-center case series, in which they reviewed the medical records and imaging studies of five patients with rounded atelectasis confirmed by histopathology or cytology. They described the clinical, radiographic, ultrasonographic, CT, and histologic findings of rounded atelectasis in these cases, and compared them with the human literature.

Methods: The authors searched the databases of three specialty veterinary medical facilities for cases of rounded atelectasis from 2007 to 2020. They included cases that had complete medical records, CT studies with features of rounded atelectasis, and histologic or cytologic confirmation. They recorded the signalment, history, laboratory results, and imaging characteristics of each case. They also reviewed the histopathology slides of each case to ensure the presence of pleural folding, which is a key feature of rounded atelectasis.

Results: The authors identified five cases that met the inclusion criteria: four cats and one dog. All cases had pleural effusion, mostly due to idiopathic chylothorax. All cases had subpleural pulmonary masses that were broad-based, homogeneously enhanced, and had indistinct margins at the hilum. The comet tail sign, which is a common feature of rounded atelectasis in humans, was seen in 14 of 26 masses. Other findings included pleural thickening, ground glass opacities, parenchymal bands, lymphadenopathy, and compensatory hyperinflation. Histopathology revealed atelectasis with pleural folding, chronic pleuritis, and mild to moderate pleural fibrosis in all cases.

Limitations: The authors acknowledged the limitations of their study, such as the small number of cases, the retrospective design, the potential selection bias, and the lack of comparison with primary pulmonary neoplasia. They also noted that the CT features of rounded atelectasis may vary depending on the chronicity and severity of the lesion, and that some features may be difficult to detect due to the small lung size of veterinary patients.

Conclusions: The authors concluded that rounded atelectasis is a rare but important differential diagnosis for subpleural pulmonary masses in veterinary patients with pleural effusion. They suggested that CT may help to differentiate rounded atelectasis from malignant neoplasia based on certain imaging features, such as subpleural location, broad-based appearance, blurred margins at the hilum, comet tail sign, and homogeneous contrast enhancement. They also recommended that histopathologists should be aware of the possibility of rounded atelectasis and look for pleural folding in cases with atelectasis and pleuritis. They hoped that their study would increase the recognition of rounded atelectasis in veterinary medicine and prevent unnecessary euthanasia or surgical intervention in the future.

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