Sciatic neuropathy caused by an intermuscular lipoma in dogs

Lipomas are common, usually slow-growing, benign tumours of mesenchymal origin that most commonly occur on the proximal limb and trunk of middle-aged to older dogs. They are rarely associated with either local invasion or malignancy, unlike infiltrative lipomas and liposarcomas, respectively. Three dogs, a 10-year-old mixed-breed female of 35 kg body weight, a 10-year-old mixed-breed male of 30 kg body weight, and an 11-year old female German shepherd of 38 kg body weight, were presented with a 3-6 month (median, 5 months) history of progressive left pelvic limb lameness and thigh swelling. A lesion affecting the soft tissue of the thigh and the left sciatic nerve was suspected in all dogs. A left thigh magnetic resonance (MR) revealed a homogenous, well circumscribed tumour in the mixed-breed dogs and two similar tumours in the German shepherd. The tumours were interposed between the semimembranosus and semitendinosus muscles. The treatment involved surgical extirpation of the tumours. A follow-up examination 12 months post operation showed mild lameness and proprioceptive deficits in the operated limb in all the dogs. The withdrawal reflex and the cranial tibial reflex were normal. Neither mass nor thickening were palpable in the thigh region. Although intermuscular lipoma is rare, it should be suspected in dogs with progressive monoparesis. Magnetic resonance is a valuable imaging method for diagnostic precision and pre-operative planning. Quick diagnosis and decompressive surgery are required to allow recovery.