1. Probable neurilemoma of the common peroneal nerve

Peripheral nerve sheath tumours (PNST) are divided into neurilemomas (schwanomas) and neurofibromas. Clinical and radiological differentiation of these tumours is difficult. Both types tend to be solitary, of fusiform shape and have a true capsule. Major nerves are splayed as they envelope the mass (see superior and inferior aspects of the MR images), whereas small nerves are usually destroyed by the tumour. Unlike neurilemomas, where both tumour and nerve may be identified within the capsule, the epineurium, neurofibromas are intimately intermixed, inseparable from normal nerve tissue. The histological hallmarks of neurilemoma are both cellular Antoni A and myxoid Antoni B regions, within the capsule, whereas a neurofibroma is composed of interlacing fascicles of wavy elongated cells that often contain abundant amounts of collagen.

Only a small percentage …