Peroneal and tibial intraneural ganglia: correlation between intraepineurial compartments observed on magnetic resonance images and the potential importance of these compartments

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>Previously the authors demonstrated that peroneal and tibial intraneural ganglia arising from the superior tibiofibular joint may occasionally extend proximally within the epineurium to reach the sciatic nerve. The dynamic nature of these cysts, dependent on intraarticular pressures, may give rise to differing clinical and imaging presentations that have remained unexplained until now. To identify the pathogenesis of these unusual cysts and to correlate their atypical magnetic resonance (MR) imaging appearance, the authors retrospectively reviewed their own experience as well as the published literature on these types of intraneural ganglia.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>A careful review of MR images obtained in 22 patients with intraneural ganglia located about the knee region (18 peroneal and four tibial intraneural ganglia) allowed the authors to substantiate three different patterns: outer (epifascicular) epineurial (20 cases); inner (interfascicular) epineurial (one case); and combined outer and inner epineurial (one case). In these cases serial MR images allowed the investigators to track the movement of the cyst within the same layer of the epineurium. All lesions had connections to the superior tibiofibular joint. Nine patients were identified as having lesions with sciatic nerve extension. Seven patients harboring an outer epineurial cyst (six in whom the cyst involved the peroneal nerve and one in whom it involved the tibial nerve) had signs of sciatic nerve cross-over, with the cyst seen in the sciatic nerve and/or other terminal branches. In only two of these cases had the cyst previously been recognized to have sciatic nerve involvement. In contrast, in one case an inner epineurial cyst involving the tibial nerve ascended within the tibial division of the sciatic nerve and did not cross over. A single patient had a combination of both outer and inner epineurial cysts; these were easily distinguished by their distinctive imaging patterns.</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>This anatomical compartmentalization of intraneural cysts can be used to explain varied clinical and imaging patterns of cleavage planes for cyst formation and propagation. Compartmentalization elucidates the mechanism for cases of outer epineurial cysts in which there are primary ascent, sciatic cross-over, and descent of the lesion down terminal branches; correlates these cysts' atypical MR imaging features; and contrasts a different pattern of inner epineurial cysts in which ascent and descent occur without cross-over. The authors present data demonstrating that the dynamic phases of these intraneural ganglia frequently involve the sciatic nerve. Their imaging features are subtle and serve to explain the underrecognition and underreporting of the longitudinal extension of these cysts. Importantly, cysts extending to the sciatic nerve are still derived from the superior tibiofibular joint. Combined with the authors' previous experimental data, the current observations help the reader understand intraneural ganglia with a different, deeper degree of anatomical detail.</jats:p></jats:sec>

Intraneural ganglion cysts: a systematic review and reinterpretation of the world's literature

“…63 Furthermore, of the 16 cases in which we were able to obtain the original full MRI series of select cases, 18,22,99,100,109,115,116,120,124,136,143,144,147,153 all had previously unrecognized joint connections: ulnohumeral joint (1), carpal joint (1), acetabulofemoral joint (3), tibiofemoral joint (4), STFJ (6), and tibiotalar joint (1) (Fig. 5).…”

“…Eleven of these cases and our reinterpretations were published. 115,116,120,124,136,143,144,147,153 The MR image reviews were all done by a fellowshiptrained musculoskeletal radiologist and the senior author, a neurosurgeon, both highly experienced in evaluating intraneural ganglion cysts.…”

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“…At that point, the peroneal and tibial nerves form the sciatic nerve, their two epineurial sheaths coalescing to form a common connective tissue sheath surrounding their individual outer epineuria. At this point the cyst may partially or completely surround the sciatic nerve, encircling the neural elementsin essence, filling a potential space with cyst fluid (producing a "wedding ring" sign 29 ). Thus transit of the cyst from the peroneal to the tibial division, or vice versa, is facilitated.…”

“…Additional subtle MR imaging findings that can be used to help identify and characterize these dynamic features are further elaborated on in a separate publication; we show that cyst extension into the sciatic nerve is underreported and underrecognized. 29 With pressure fluxes, we also need to consider the phenomenon of distal descent. In Case 3 considerable cyst descent was demonstrated within the tibial nerve component; the cyst traveled 9 inches below knee level-in other words, distal to the level of the superior tibiofibular joint.…”

Intraneural ganglia: a clinical problem deserving a mechanistic explanation and model

“…Different theories, without a scientific basis, have been proposed. 4,[6][7][8]15,19,20,24,27 The articular (synovial) theory, 42,45 based on robust clinical, imaging, and histological evidence, 11,[39][40][41][42]44,45,47,49,50 provides a logical, consistent explanation that clarifies and unifies the observations made by many over the years. Developed on the prototype of the peroneal nerve ganglion cysts, the theory can be extrapolated to intraneural ganglion cysts involving other nerves.…”