Diagnosis: Spinner Classification Stage III intraneural ganglion of the peroneal nerve
Discussion:Intraneural ganglion cysts are mucinous cysts forming within the epineurium of peripheral nerves. This rare occurrence most commonly involves the peroneal nerve. Much of our understanding of the pathogenesis, staging, and history of intraneural ganglia comes from the work of Dr. Robert Spinner at the Mayo Clinic. His “unifying articular theory” stipulates that tibiofibular ganglion cysts, both extra and intraneural, originate from the superior tibofibular joint, and that in the intraneural variety a connection to the articular branch of the peroneal nerve serves as a conduit for fluid to extend, along a path of least resistance, into the deep peroneal nerve, the common peroneal nerve, and even the sciatic nerve.
Patients with peroneal intraneural ganglion cysts share a common clinical presentation and progression of symptoms, referable to the degree of involvement of the deep peroneal nerve. The initial symptom is poorly localized leg pain, which progresses to neuropathic pain in the DPN distribution, then to foot drop secondary to weakness of the tibialis anterior muscle.
Staging of tibiofibular ganglia can be accomplished with MRI.
Extraneural cysts from the superior tibiofibular joint are classified as Stage 0. Intraneural cysts are staged according to their predictable progression from the articular nerve (Stage I), to the proximal deep peroneal nerve (Stage II), the common peroneal nerve (Stage III), and finally the sciatic nerve (Stage IV).
Treatment is aimed at intraneural cyst decompression and elimination of the pathway of fluid extension from the joint into the deep peroneal nerve. The latter can beaccomplished via ligature of the supplying articular nerve branch or by synovectomy of the superior tibiofibular joint. Recurrences were common in early treatment of IGCs;however, these predictably occurred when elimination of articular nerve supply to the ganglion cyst was not accomplished, either when treated with simple nerve aspirationor decompression with non-identification and/or eradication of the articular branch.
