Sonographic Detection of Knee Neurilemmoma: A Case Report and Literature Review

Neurilemmomas, although relatively rare, are the most common type of peripheral nerve tumor in adults. This article reports a 52-year-old man with a palpable, painful mass located distal to the popliteal fossa causing intermittent radiating numbness down to the calf and foot for 4 months. Baker’s cyst compressing the posterior tibial nerve or neurogenic tumor was suspected. Sonographic examination revealed a well-defined heterogeneous mass, located within the muscular layer, communicating with the posterior tibial nerve. The pathology was found to be a neurilemmoma. Symptoms of leg pain and numbness resolved after surgical removal of the tumor. The diagnosis of posterior tibial nerve neurilemmoma is often delayed because it is mistaken for Baker’s cyst or lumbosacral radiculopathy. Sonographic examination is useful in the initial assessment, because it helps differentiate the origin and characteristics of a palpable mass.