• Robert J Spinner, Huan Wang, Marie-Noëlle Hébert-Blouin, John A Skinner, and Kimberly K Amrami.
• Department of Neurologic Surgery, Mayo Clinic, Rochester, MN 55905, USA. spinner.robert@mayo.edu
• Acta Neurochir (Wien). 2009 Jan 1; 151 (1): 89-98.

BackgroundA predictable mechanism and stereotypic patterns of peroneal intraneural ganglia are being defined based on careful analysis of MRIs. Peroneal and tibial intraneural ganglia extending from the superior tibiofibular joint which extend to the level of the sciatic nerve have been observed leading to the hypothesis that sciatic cross-over could exist. Such a cross-over phenomenon would allow intraneural cyst from the peroneal nerve by means of its shared epineurial sheath within the sciatic nerve to cross over to involve the tibial nerve, or vice versa from a tibial intraneural cyst to the peroneal nerve.Method And FindingsOne patient with a peroneal intraneural ganglion and another with a tibial intraneural ganglion each underwent a knee MR arthrogram. These studies were not only definitive in demonstrating the communication of the cyst to the superior tibiofibular joint connection but also in confirming sciatic cross-over. Contrast injected into the knee could be demonstrated tracking to the superior tibiofibular joint and then proximally into the common peroneal or tibial nerve respectively, crossing over at the sciatic nerve, and then descending down the tibial and peroneal nerves. The arthrographic findings mirrored MR images upon their retrospective review.ConclusionsThis study provides direct in vivo proof of the nature of sciatic cross-over theorized by critical review of MRIs and/or experimental dye injections done in cadavers. This study is important in clarifying the potential paths of propagation of intraneural cysts at points of major bifurcation.

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