Epineurial compartments and their role in intraneural ganglion cyst propagation: An experimental study

Abstract

New patterns of intraneural ganglion cyst formation are emerging that have not previously been explained in current pathoanatomic terms. We believe there are three important elements underlying the appearance of these cysts: (a) an articular branch of the nerve that connects to a nearby synovial joint; (b) ejected synovial fluid following the path of least resistance along tissue planes; and (c) the additional effects of pressure and pressure fluxes. The dynamic nature of cyst formation has become clearly apparent to us in our clinical, operative and pathologic practice, but the precise mechanism underlying the process has not been critically studied. To test our hypothesis that a fibular (peroneal) or tibial intraneural cyst derived from the superior tibiofibular joint could ascend proximally into the sciatic nerve, expand within it and descend into terminal branches of this major nerve, we designed a series of simple, qualitative laboratory experiments in two cadavers (four specimens, six experiments). Injecting dye into the outer or "epifascicular" epineurium of the fibular and the tibial nerves we observed its ascent, cross over and descent patterns in three of three specimens as well as its cross over after an outer epineurial sciatic injection. In contrast, injecting dye into the inner or "interfascicular" epineurium led to its ascent within the tibial nerve and its division within the sciatic nerve in one specimen and lack of cross over in a sciatic nerve injection. Histologic cross-sections of the nerves at varying levels demonstrated a tract of disruption within the outer epineurium of the nerve injected and the nerve(s) into which the dye, after cross over, descended. Those specimens injected in the inner epineurium demonstrated dye within this tract but without disruption of or dye intrusion into the outer epineurium. In no case did the dye pass through the perineurial layers. Coupled with our observations in previous detailed studies, these anatomic findings provide proof of concept that sciatic cross over occurs due to the filling of its common epineurial sheath; furthermore, these findings, support the unifying articular theory, even in cases wherein patterns of intraneural ganglion cyst formation are unusual. Additional work is needed to be done to correlate these anatomic findings with magnetic resonance imaging and surgical pathology.

Cross‐over: A generalizable phenomenon necessary for secondary intraneural ganglion cyst formation

“…First confronted by an unexplained clinical outlier in the literature from the pre-MRI (magnetic resonance imaging) era (Jacobs et al, 1975), then puzzled by the MRIs in several of our own patients with multiple intraneural ganglion cysts within sciatic, tibial, fibular, and sural nerves which were all derived from a single joint of origin (i.e., the superior tibiofibular joint), we put forth an anatomic explanation for this new pattern and concept (Spinner et al, 2007a,c): cyst fluid ascending up the primarily ''affected'' nerve could reach the level of the sciatic nerve, fill its common epineurial sheath and spread circumferentially (cross over), at which time pressure fluxes could result in further ascent up the sciatic, descent down the same parent nerve or one of its branches (i.e., the sural), or descent down the opposite, previously ''unaffected'' fibular or tibial nerves. We then confirmed the phenomenon of cross-over and bidirectional flow in an experimental model using selective dye injections (Spinner et al, 2007d).…”

Dynamic phases of peroneal and tibial intraneural ganglia formation: a new dimension added to the unifying articular theory

“…In dye studies, injection of the outer epineurium allows observation of primary ascent, sciatic cross-over, and terminal branch descent in an experimental model and a barrier between the outer and inner epineuria. 37,41 We invoke these anatomically relevant data to draw a clinical corollary. We have identified three sequential phases of peroneal and tibial intraneural ganglia cyst formation (Fig.…”

Intraneural Ganglion Cyst of the Sciatic Nerve Treated Using Arthroscopic Hip Surgery: A Case Report

“…Recently, the articular theory has been the most widely accepted. According to the articular theory, INGCs are formed as the joint fluid under pressure passes through the capsular defect and propagates along the articular branch of the nerve . Joint fluid dissects proximally up the articular branch within the epineurium along the path of least resistance …”

“…Spinner et al found that dye injected in the outer epineurium remained in the outer epineurium, whereas dye injected in the inner epineurium crossed over to the adjacent nerve fascicle . In addition, it was suggested that sciatic crossover between tibial and common peroneal nerve occurs when INGCs spread along the outer as opposed to inner epineurium.…”