Spinner, Robert J.

Object 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. Methods 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. Conclusions 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.

✓The common peroneal nerve is the peripheral nerve most often affected by intraneural ganglion cysts. Although the pathogenesis of these cysts has been the subject of controversy in the literature, it is becoming increasingly evident that they are of articular origin. Recent recognition of this fact has proven to be significant in reducing recurrences and improving treatment outcomes for patients. The authors present a stepwise method of assessing and treating peroneal intraneural ganglion cysts.

Object The pathogenesis of intraneural ganglia has been a controversial issue for longer than a century. Recently the authors identified a stereotypical pattern of occurrence of peroneal and tibial intraneural ganglia, and based on an understanding of their pathogenesis provided a unifying articular explanation. Atypical features, which occasionally are observed, have offered an opportunity to verify further and expand on the authors' proposed theory. Methods Three unusual cases are presented to exemplify the dynamic features of peroneal and tibial intraneural ganglia formation. Results Two patients with a predominant deep peroneal nerve deficit shared essential anatomical findings common to peroneal intraneural ganglia: namely, 1) joint connections to the anterior portion of the superior tibiofibular joint, and 2) dissection of the cyst along the articular branch of the peroneal nerve and proximally. Magnetic resonance (MR) images obtained in these patients demonstrated some unusual findings, including the presence of a cyst within the tibial and sural nerves in the popliteal fossa region, and spontaneous regression of the cysts, which was observed on serial images obtained weeks apart. The authors identified a clinical outlier, a case that could not be understood within the context of their previously reported theory of intraneural ganglion cyst formation. Described 32 years ago, this patient had a tibial neuropathy and was found at surgery to have tibial, peroneal, and sciatic intraneural cysts without a joint connection. The authors' hypothesis about this case, based on their unified theory, was twofold: 1) the lesion was a primary tibial intraneural ganglion with proximal extension followed by sciatic cross-over and distal descent; and 2) a joint connection to the posterior aspect of the superior tibiofibular joint with a remnant cyst within the articular branch would be present, a finding that would help explain the formation of different cysts by a single mechanism. The authors proved their hypothesis by careful inspection of a recently obtained postoperative MR image. Conclusions These three cases together with data obtained from a retrospective review of the authors' clinical material and findings reported in the literature provide firm evidence for mechanisms underlying intraneural ganglia formation. Thus, expansion of the authors' unified articular theory permits understanding and elucidation of unusual presentations of intraneural cysts. Whereas an articular connection and fluid following the path of least resistance was pivotal, the authors now incorporate dynamic aspects of cyst formation due to pressure fluxes. These basic principles explain patterns of ascent, cross-over, and descent down terminal nerve branches based on articular connections, paths of diminished resistance to fluid flow within recognized anatomical compartments, and the effects of fluctuating pressure gradients.

Object The suprascapular nerve may become entrapped as it travels deep to the suprascapular ligament, necessitating decompression. The present study was performed to verify the feasibility of a minimally invasive, endoscopically assisted technique for decompressing the suprascapular nerve in the supraspinous fossa. Methods The authors performed dissection and decompression of the suprascapular ligament using an endoscopically assisted technique via a 3-cm skin incision in 10 adult cadavers (20 sides). Measurements were also made of the depth from the skin to the suprascapular ligament. Results A mean depth of 4 cm was necessary to reach the suprascapular ligament from the skin surface. With the authors' approach, no obvious injury occurred to the suprascapular or other vicinal neurovascular structures (such as the spinal accessory nerve and suprascapular vessels). Conclusions The results of this cadaveric study demonstrate that access to the suprascapular nerve can be obtained endoscopically via a small suprascapular incision. This approach obviates a large incision, entry into the glenohumeral joint, and reduces the risk of spinal accessory nerve injury in the posterior cervical triangle, or atrophy of the trapezius or supraspinatus muscles from a standard larger dissection. To the authors' knowledge an endoscopically assisted approach to decompressing the suprascapular nerve as it courses deep to the suprascapular ligament has not been reported previously.

The chondroepitrochlearis muscle is an extremely rare muscle, arising from the pectoralis major, crossing over the neurovascular bundle in the axilla and inserting into the brachial fascia and medial epicondyle of the humerus. This paper presents the first known neurological complication due to the chondroepitrochlearis muscle.

Abstract OBJECTIVE AND IMPORTANCE Heterotopic ossification (“neuritis ossificans”) is among the least frequently encountered reactive lesions in peripheral nerves. Only two cases have been described previously, one in the median nerve of a 34-year-old man, and the other in the ulnar nerve of an adult woman. The architecture of this lesion is distinctly zonal. Consisting of a central fibroblastic core, an intervening zone of osteoid production, and a peripheral layer of ossification, the pattern is remarkably similar to that of myositis ossificans. This similarity and the occurrence of the process in superficial nerves have led to speculation that trauma plays a role in its pathogenesis; this hypothesis remains unproved. We describe two additional cases of neuritis ossificans. CLINICAL PRESENTATION One patient, a 41-year-old man, experienced pain and numbness in the left leg for several months but had no history of local trauma. A mass was detected in the saphenous nerve. The second patient, a 16-year-old boy, noted subacute onset of pain in the popliteal fossa and decreased sensation in the distribution of the lateral sural cutaneous nerve. A mass was found within the tibial nerve at the knee level. INTERVENTION In each patient, resection of the mass required sacrifice of a segment of the nerve. CONCLUSION In each patient, the mass was composed of fibrovascular tissue with osteoid and bone deposition arranged in a zonal pattern. The ossifying process was intraneural but encased rather than directly involving nerve fascicles. These exceptionally intact examples of neuritis ossificans underscore its resemblance to myositis ossificans. Nerve-sparing resection of such masses is not always possible.