Case series summary Lung lobe torsion is rare in cats. The aim of this multi-institution retrospective study was to describe clinical and diagnostic findings, treatments and outcomes of lung lobe torsion (LLT) in 10 cats. Dyspnoea and tachypnoea were the most common clinical signs. Pleural effusion was present in nine cats at presentation. Fluid analysis confirmed chylothorax in three cats. Nine cats underwent CT and five cats had thoracic radiographs taken. A diagnosis was made preoperatively in six cats, while in the other four cats it was made at exploratory thoracotomy. Affected lung lobes were the right cranial (n = 4/11), left cranial (n = 4/11) and right middle (n = 3/11). One cat had a concurrent torsion of two lung lobes. Lung lobectomy was successfully performed in all cases. Based on clinical, diagnostic and lung histopathology findings, three cats had idiopathic and seven cats secondary LLT. Intraoperative complications included hypotension and hypothermia in four and five cats, respectively. Postoperative complications occurred in six cats and lead to euthanasia or death in four cats, whereas complications resolved in the other two cats. Three cats were euthanased within 5 weeks of discharge. For the three cats surviving long term, including one euthanased at 252 days postoperatively, owner-described outcomes and quality of life were considered good to excellent. Relevance and novel information Secondary LLT associated with underlying thoracic pathology was associated with high complication rates and poor outcomes. Long-term outcomes of cats undergoing surgery for LLT and surviving the perioperative period were deemed good to excellent.

A 10‐year‐old female spayed Maine Coon presented with lethargy, weight loss and severe dyspnoea. Radiographs showed mediastinal enlargement and marked pleural effusion. Thoracocentesis yielded a highly protein‐rich transudate with macrophages predominating. Computed tomography identified a large cystic mediastinal structure with a typical peripheral contrast‐enhancing rim, but fluid contents with a high attenuation of 35HU and internal contrast‐enhancing projections raising concern for neoplasia. However, mediastinal cytology failed to demonstrate neoplastic cells, but instead ciliated columnar epithelium most consistent with a thymic branchial cyst. The cat underwent median thoracotomy and mediastinal mass resection and is well 6 months postoperatively, with no evidence of recurrence. Histopathology with immunohistochemistry diagnosed thymic carcinoma, with branchial duct remnants. This report highlights the diagnostic challenge of mediastinal cystic lesions and the possible concurrent presence of a non‐neoplastic and a malignant neoplastic process.