Femoral mononeuropathy caused by a malignant sarcoma: two case reports.

A 9-year old miniature poodle and a 6-year old American Staffordshire terrier were evaluated for slowly progressive lameness and atrophy of the left pelvic limb. Neurological examinations of both animals were consistent with femoral nerve lesions. In both cases, neoplastic masses were identified within the left psoas muscle, invading the left femoral nerve or, in one case, its nerve roots. Ultrasound-guided fine needle aspirate and histopathological examination of the masses revealed that these were malignant sarcomas. Femoral mononeuropathies are very rare in dogs, and most descriptions of femoral nerve lesions are caused by traumatic injuries. Descriptions of neoplastic processes affecting the femoral nerve are limited to peripheral nerve sheath tumours (PNST). These cases provide the first descriptions of malignant neoplasms other than PNSTs that infiltrate the femoral nerve or its nerve roots and cause unilateral femoral mononeuropathy and lameness of obscure origin.