Sural Intraneural Ganglion Cysts Are Joint-related

The recent article by Kim and Kim [1] provides a valuable case of a rare sural intraneural ganglion cyst to the literature. We offer yet another example to highlight recent developments in our understanding of this entity. A 42-year-old woman presented with a 6 month history of the spontaneous onset of moderately severe pain developing in the right lateral rearfoot in the retrolateral malleolar region with radiating dysesthesias into the dorsolateral foot. Symptoms were worse with standing or with activity. Exam revealed a 3×2 cm soft tissue tubular mass along the course of the sural nerve which had features consistent with a ganglion cyst. It was tender to palpation. Percussion produced radiating paresthesias in the sural nerve distribution. Sensation was intact on the dorsal foot to light touch. Magnetic reconance imaging (MRI) demonstrated a sural intraneural ganglion cyst with a joint connection to the subtalar joint (Figs. 1, ​,2).2). At operation, this articular branch connection was identified, ligated and resected. The patient had full recovery immediately postoperatively; there was no clinical evidence of persistent pain or cyst at last follow-up examination. Fig. 1 Conventional MRI of a patient with sural intraneural ganglion originating from subtalar joint. Serial coronal T2-weighted fast spin echo (FSE) images with fat suppression from posterior to anterior demonstrates an intraneural cyst arising from the lateral ... Fig. 2 Three-dimensional rendering of conventional magnetic resonance images obtained in this patient with a sural intraneural ganglion cyst. Maximum intensity projection image created from the same series as Fig. 1 shows the entire course of the cyst (asterisk) ... As Kim and Kim [1] point out, the pathogenesis of these cysts has been controversial and poorly understood. Recent reports have clarified this. Layers of robust evidence have substantiated an articular origin for all types of intraneural cysts first at the prototypic site (the common fibular nerve) and then at other joints throughout the appendicular skeleton and axial spine [2,3]. The unifying articular (synovial) theory has been shown to be generalizable and universal. Joint connections must be assumed to be present. We have emphasized the difficulties in identifying the joint connection with imaging and at operation. Experience with both can reliably and reproducibly identify the joint connection. High resolution imaging (MRI or computed tomography imaging with or without arthrography; or ultrasound) with conventional or 3-dimensional renderings may show convincingly a seemingly occult joint connection [3,4], even when reported by others not to be present. The consistent articular connection has fostered an understanding of the principles of these cysts. A capsular defect allows the passage of joint fluid to pass from the joint (often degenerative) along an articular branch and into the parent nerve. Propagation follows the pass of least resistance within the epineurium of nerve. Intra-articular pressure and pressure fluxes influence cyst dimensions. We have identified 9 cases of sural intraneural ganglia (Appendix). Of these, joint connections were only found in 3 instances: twice to the subtalar joint and once to the calcaneocuboid joint. Nevertheless, we are confident that joint connections were present in all of the remaining cases in the literature, including the one by Kim and Kim [1]. These joint connections can be predicted and must be anticipated. The articular branch anatomy of the sural nerve [5] would explain all of the locations of these cysts (Fig. 3). The unifying articular theory could explain all of their patterns of propagation [2,3]. Fig. 3 The anatomy and pathoanatomy of known and potential sites of sural intraneural ganglion cysts. The drawing of the normal anatomy was based on descriptions by anatomists [5]. The confirmed joint-related sites of origin (subtalar and calcaneocuboid joints) ... Understanding the pathogenesis can help target surgery so as to simplify it. Surgery should include ligating or resecting the articular branch near the joint. The cyst itself need not be resected as it will be resorbed as long as the connection is disrupted. This approach minimizes intraneural dissection and eliminates intraneural recurrence, which is known to occur with high rates and was documented in several of these sural examples (Appendix). We believe that such recurrence would likely have been present in other patients (even those who were asymptomatic) if postoperative imaging had been performed. Resecting the nerve, while possible in the case of a distal cutaneous nerve (such as the sural nerve) and has been performed in several cases, could still result in intraneural (distal) recurrence. Furthermore, nerve sacrifice can not be extrapolated to other cases of intraneural ganglia involving major mixed peripheral nerves. Knowledge of current pathogenesis and experience with the imaging and operative findings with these rare cysts will improve outcomes and eliminate intraneural recurrences.