Peroneal intraneural ganglion cyst
Peroneal intraneural ganglion cysts are an uncommon cause of a cystic lesion around the knee. Intraneural ganglion cysts are benign mucinous lesions have been reported in many peripheral nerves, and not uncommonly form in the common peroneal nerve.
These lesions can present as a mass and/or with neuropathy symptoms.
The etiology of these ganglia is still debated, but the "articular" etiology is the leading explanation for their formation: a small tear in the joint capsule of an adjacent joint allows fluid to track along the nerve's epineurium. A "cyst" then forms in the nerve with changes in volume/pressure in the joint tracking into the nerve 4. In the case of the common peroneal nerve ganglion cyst, the joint involved is the superior tibiofibular joint.
With both imaging modalities look for signs of neuropathy (e.g. muscle atrophy) in the nerve's distribution.
- multiloculated fluid collection in intimate connection with the common peroneal nerve
- T2 hyperintense lesion tracking along the course of the common peroneal nerve
- rarely, there is extension into the tibial nerve as well
- on MR arthrography, fluid tracks from the adjacent joint to the nerve
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