Ultrasonographic Features of Pleural Thickening in Cats With Pulmonary Carcinoma and Pleural Effusion: A Retrospective Descriptive Study

BACKGROUND: Pleural involvement is an important but poorly described manifestation of feline pulmonary carcinoma. Thoracic ultrasonography may identify pleural abnormalities and accessible targets for cytologic sampling in cats with pleural effusion. OBJECTIVES: To describe ultrasonographic features of pleural thickening in cats with pulmonary carcinoma and pleural effusion and summarise cytologic findings from pleural effusion and ultrasound-guided lesion sampling. METHODS: Medical records from one referral hospital were retrospectively reviewed for cats with pulmonary carcinoma or metastatic epithelial neoplasia consistent with pulmonary origin, pleural effusion, and stored thoracic ultrasound images. Images were reviewed in consensus by three observers for distribution, location, shape, maximal thickness, echogenicity, homogeneity, and suspected intercostal muscle invasion. RESULTS: Twenty-two cats were included. Pleural thickening was recorded in all cats. Thickening was classified as diffuse in 12 cats, focal in 6, and multifocal in 4; however, scanning was not systematic across all thoracic regions. The representative or measured pleural abnormality was in the cranial pleural region in 18 cats. Maximal pleural thickness was 5.6 ± 3.3 mm (median, 4.9 mm; range, 1.2-16.2 mm). Suspected intercostal muscle invasion was recorded in eight cats. Neoplastic cells were identified in pleural effusion cytology in 15/20 cats. Six cats underwent ultrasound-guided lesion sampling; cytologic or histopathologic findings were supportive of carcinoma in all 6, including 1 confirmed by biopsy. CONCLUSIONS: In this selected cohort, thoracic ultrasonography identified pleural thickening with variable morphology. Thickened pleura may represent a feasible sampling target, but prospective studies are needed to determine prevalence, distribution, sensitivity, and specificity.