Not tarsal tunnel syndrome: a malignant "Triton" tumour of the tibial nerve.

A 23 year old male patient presented with a venous thrombosis in the right calf. This was followed by symptoms, signs and electromyographic findings suggestive of a tarsal tunnel syndrome. Symptoms were briefly relieved by surgical division of the flexor retinaculum. Subsequently, patient developed swelling in the calf and was found to have a malignant ("Triton") tumour of the tibial nerve and required above knee amputation. In the absence of obvious foot or ankle deformity, caution should be exercised in making the diagnosis of tarsal tunnel syndrome.