BENIGN CRANIAL MEDIASTINAL LESIONS IN 3 CATS

Cranial mediastinal lesions were detected in three cats, associated wi th respiratory impairment (case one), spontaneous pneumothorax (case t wo) and myasthenia gravis (case three), respectively. On gross and his tological examination, the first case was considered either a lymphang ioma or a branchial cystic mass of the thymic region of the mediastinu m; a cystic lesion was suggested by sonographic detection of multiple anechoic cavitations within a circumscribed mass, while fine needle as piration cytology excluded lymphosarcoma. The second case was diagnose d histologically as a cystic thymoma, but: the third case was not exam ined microscopically. The masses were amenable to surgical excision in the first two cats, while this proved unnecessary in the third case b ecause of resolution following treatment with dexamethasone. Corticost eroid responsiveness was unhelpful in distinguishing between these ben ign lesions and lymphosarcoma, as in two cases there was a partial or complete response to dosing with prednisolone or dexamethasone. These cases are presented to emphasise that conditions other than lymphosarc oma can produce cranial mediastinal lesions in cats, and that the prog nosis for surgical treatment of lymphangiomas, multilocular thymic cys ts and cystic thymomas can be excellent.