Peroneal intraneural ganglia

Preoperative Imaging of Intraneural Ganglion Cysts: A Critical Systematic Analysis of the World Literature

BACKGROUND

Advancements in imaging and an understanding of the pathomechanism for intraneural ganglion cyst formation have led to increased awareness and recognition of this lesion. However, the precise role of imaging has been advocated for but not formally evaluated.

METHODS

We performed a systematic review of the world literature to study the frequency of imaging used to diagnose intraneural ganglion cysts at different sites and compared trends in identifying joint connections.

RESULTS

We identified 941 cases of intraneural ganglion cysts, of which 673 had published imaging. Magnetic resonance imaging (MRI, n = 527) and ultrasonography (US, n = 123) were the most commonly reported. They occurred most frequently in the common peroneal nerve (n = 570), followed by the ulnar nerve at the elbow (n = 88), and the tibial nerve at the ankle (n = 58). A joint connection was identified in 375 cases (48%), with 62% of MRIs showing a joint connection, followed by 16% on US, and 6% on computed tomography (CT). MRI was statistically more likely to identify a joint connection than was US (P < 0.01). In the last decade, joint connections have been identified with increasing frequency using preoperative imaging, with up to 75% of cases reporting joint connections.

CONCLUSIONS

Preoperative imaging plays an important role in establishing the diagnosis of intraneural ganglion cyst as well as treatment planning. Imaging has proved superior to the sole reliance of operative exposure to identify a joint connection, which is necessary to treat the underlying disease. Failure to identify cyst connections on imaging can result in an inability to truly address the underlying pathoanatomy at the time of definitive surgery, leading to a risk for clinical recurrence. Therefore, management should be guided by an intersection between new knowledge presented in the literature, clinical expertise, and surgeon experience.

Peroneal Nerve Palsy Due to Subparaneurial Ganglion Cyst, a Rare Variant of Intraneural Ganglion Cyst

Intraneural ganglion cysts are rare mucinous cysts originating within the epineurium of peripheral nerves. Although ganglion cysts are the most frequent tumors of the upper and lower extremities, ganglion cysts rarely result in peripheral nerve compression. We report a case of a 30-year-old patient who presented with foot drop due to subparaneurial ganglion cyst, a variant of an intraneural ganglion cyst. Characteristic magnetic resonance imaging findings were essential in the preoperative diagnosis of intraneural ganglion cyst. The common peroneal nerve and its branches were recognized and traced to its bifurcation during the operation. The articular branches were addressed. The mucious content of the ganglion was typically found to be located within the subparaneurial compartment. Incision of the subparaneurial ganglion cyst was performed, and mucinous content was evacuated. At 2 months after the surgery, paralyzed peroneal nerve was recovered completely. Therefore, early diagnosis of intraneural ganglion, precise identification of the pathology, and proper treatment of the articular branch with atraumatic dissection of ganglion cyst are essential in the successful management of this rare lesion.

Intraneural ganglion cyst of the ulnar nerve in an unusual location: A case report

INTRODUCTION

Intraneural ganglion cysts are benign, mucinous, non-neoplastic lesions of the peripheral nerves. While the most common location of intraneural ganglion cysts is the ulnar nerve and its branches, intraneural ganglion cyst involving the superficial branch of the ulnar nerve has not yet been reported.

PRESENTATION OF CASE

A-25-year-old woman presented with pain and a palpable mass in the hypothenar region of the volar side of her right hand. Her neuromuscular examination was normal. The pain was unresponsive to nonsurgical treatments. After confirming with imaging modalities, the initial diagnosis was considered as an intraneural ganglion cyst arising from superficial ulnar nerve. Excision of the ganglion and exploration of the articular branch (if seen in operation) decision was undertaken by the senior author. Whether MRI or intraoperative exploration, not identified an articular branch.

DISCUSSION

Intraneural ganglion cysts of peripheral nerves may be seen in miscellaneous locations in the body. However, to our knowledge, an intraneural ganglion cyst involving the superficial branch of the ulnar nerve is unique. While a variety of theories have been proposed to enlighten the etiopathogenesis of intraneural ganglia, the latest and most affirmed is the unifying articular (synovial) theory.

CONCLUSION

Intraneural ganglion cysts may be seen on the hypothenar side of the palm. The etiology and treatment of choice are closely associated with each other in this rare disorder. It is important to realize a related articular branch, otherwise the origin of cyst formation remains, and this may cause other para-articular cysts.

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

OBJECTIVE The etiology of intraneural ganglion cysts has been controversial. In recent years, substantial evidence has been presented to support the articular (synovial) theory for their pathogenesis. The authors sought to 1) perform a systematic review of the world's literature on intraneural cysts, and 2) reinterpret available published MR images in articles by other authors to identify unrecognized joint connections. METHODS In Part 1, all cases were analyzed for demographic data, duration of symptoms, the presence of a history of trauma, whether electromyography or nerve conduction studies were performed, the type of imaging, surgical treatment, presence of a joint connection, intraneural cyst recurrence, and postoperative imaging. Two univariate analyses were completed: 1) to compare the proportion of intraneural ganglion cyst publications per decade and 2) to assess the number of recurrences from 1914 to 2003 compared with the years 2004-2015. Three multivariate regression models were used to identify risk factors for intraneural cyst recurrence. In Part 2, the authors analyzed all available published MR images and obtained MR images from selected cases in which joint connections were not identified by the original authors, specifically looking for unrecognized joint connections. Two univariate analyses were done: 1) to determine a possible association between the identification of a joint connection and obtaining an MRI and 2) to assess the number of joint connections reported from 1914 to 2003 compared with 2004 to 2015. RESULTS In Part 1, 417 articles (645 patients) were selected for analysis. Joint connections were identified in 313 intraneural cysts (48%). Both intraneural ganglion cyst cases and cyst recurrences were more frequently reported since 2004 (statistically significant difference for both). There was a statistically significant association between cyst recurrence and percutaneous aspiration as well as failure to disconnect the articular branch or address the joint. In Part 2, the authors identified 43 examples of joint connections that initially went unrecognized: 27 based on their retrospective MR image reinterpretation of published cases and 16 of 16 cases from their sampling of original MR images from published cases. Overall, joint connections were more commonly found in patients who received an MRI examination and were more frequently reported during the years 2004 to 2015 (statistically significant difference for both). CONCLUSIONS This comprehensive review of the world's literature and the MR images further supports the articular (synovial) theory and provides baseline data for future investigators.

Peroneal intraneural ganglion cysts at the fibular neck: the layered "U" surgical approach to the articular branch and superior tibiofibular joint

BACKGROUND

Intraneural ganglia most commonly occur within the peroneal nerve near the fibular neck. Disconnection of the articular branch is required in their treatment. Surgical intervention can be challenging because of unfamiliarity with the region or scarring from previous surgery.

METHOD

We present the layered "U" technique for peroneal intraneural ganglia with clinical examples. Dissection is carried down in parallel to the U-shaped course of the articular branch to provide optimal visualization and avoid injury to major branches of the nerve.

CONCLUSION

This pathoanatomic approach provides direct and safe exposure of the articular branch of the common peroneal nerve.

Peroneal and tibial intraneural ganglion cysts in children

BACKGROUND/AIMS

Intraneural ganglion cyst is a rare and underrecognized clinical entity in the pediatric population, which may cause pain as well as motor and sensory neurological deficits. This study presents 4 pediatric patients harboring ganglion cysts involving the peroneal and tibial nerves.

METHODS

Data encompassing pre- and postoperative analyses of 4 pediatric patients with intraneural ganglion cyst was evaluated.

RESULTS

Out of these 4 patients, 3 had an intraneural ganglion cyst involving the peroneal nerve, and 1 patient had his tibial nerve involved. Two patients were operated for recurrent ganglion cysts with severe postoperative neurological deficits, after preceding operations in other institutions. The other 2 patients had no history of previous surgery, and they had their initial surgical treatment in our institute for primarily diagnosed ganglion cysts. With a mean follow-up of 24 months, all patients experienced pain relief. Significant improvement of motor deficits was achieved in 3 patients. No recurrences were encountered during the 24-month follow-up.

CONCLUSION

Intraneural ganglion cysts in children can be treated with excellent outcome in experienced and dedicated centers, which specialize in peripheral nerve microsurgery.

A ganglion within the ulnar nerve and communication with the distal radioulnar joint via an articular branch: case report

An intraneural ganglion is rare, and involvement of an articular nerve may suggest a possible pathogenesis. We report an intraneural ganglion of the ulnar nerve with a connection to the distal radioulnar joint via the articular branch. We excised the ganglion, the stalk, and the articular branch. To date, there has been no recurrence.

Evaluation of intraneural ganglion cysts using three-dimensional fast spin echo-cube

PURPOSE

To compare conventional two-dimensional fast spin echo (FSE) MRI sequences with a three-dimensional FSE extended echo train acquisition method, known as Cube, in the evaluation of intraneural ganglion cysts. Also, to demonstrate that Cube enables the consistent identification and thorough characterization of the cystic joint connection, and therefore improves patient care by superior preoperative planning.

MATERIALS AND METHODS

Six patients with intraneural ganglia in the knee region (five involving the peroneal and one the tibial nerve) were evaluated using both conventional FSE MR sequences and the Cube sequence. Studies were interpreted by the consensus of three board certified musculoskeletal radiologists and one peripheral nerve neurosurgeon. Surgical correlation was available in five of the six cases.

RESULTS

Both imaging methods demonstrated the cysts and at least part of their joint connections after variable amount of postprocessing. Cube proved superior to conventional imaging in its ability to acquire isotropic data that could easily be reconstructed in any plane and its ability to resolve fine anatomical details.

CONCLUSION

Cube is a new MR pulse sequence that enables the consistent identification of the intraneural ganglion cyst joint connection. We believe that improved visualization and characterization of the entire cyst will improve patient outcomes by facilitating more accurate surgical intervention.

Extreme intraneural ganglion cysts

Object

The mechanism responsible for exceptional examples of intraneural ganglia with extensive longitudinal involvement has not been understood. Such cases of intraneural cysts, seemingly remote from a joint, have been thought not to have articular connections. Decompression and attempted resection of the cyst has led to intraneural recurrence and poor neurological recovery. The purpose of this report is not only to clarify the pathogenesis of these cysts, but also to discuss their treatment based on modern concepts of intraneural ganglia.

Methods

Two examples of extreme longitudinal propagation of intraneural ganglia are presented.

Results

A patient with a moderate tibial neuropathy was found to have a tibial intraneural ganglion. Prospective interpretation of the MR imaging study demonstrated the cyst's origin from the posterior portion of the superior tibiofibular joint (STFJ), with proximal extension within the sciatic nerve to the lower buttock region. Communication between the STFJ and the cyst was confirmed with direct knee MR arthrography. The tibial intraneural cyst was treated successfully by a relatively limited exposure in the distal popliteal fossa: the cyst was decompressed, the articular branch disconnected, and the STFJ resected. Postoperatively, the patient improved neurologically and there was no evidence of recurrent cyst on postoperative MR imaging. A second patient, previously reported by another group, was reexamined 22 years after surgery. This patient had an extensive peroneal intraneural ganglion that extended into the sciatic nerve from the knee to the buttock; no joint connection or recurrent cyst had initially been described. In this patient, the authors hypothesized and established with MR imaging the presence of both: a joint connection to the anterior portion of the STFJ from the peroneal articular branch as well as recurrent cyst within the peroneal and tibial nerves.

Conclusions

This paper demonstrates that extreme intraneural cysts are not clinical outliers but represent extreme examples of other more typical intraneural cysts. They logically obey the same principles, previously described in the unified articular (synovial) theory. The degree of longitudinal extension is probably due to high intraarticular pressures within the degenerative joint of origin. The generalizability of the mechanistic principles is highlighted by the fact that these 2 cases, involving the tibial and the peroneal nerve respectively, both extended well distant (that is, to the buttock) from the STFJ via their respective articular branch of origin. These extensive intraneural cysts can be treated successfully by disconnecting the affected articular branch and by resection of the joint of origin, rather than by a more aggressive operation resecting the cyst and cyst wall.

An ulnar intraneural ganglion arising from the pisotriquetral joint: case report

Intraneural ganglions of the hand are rare and remain poorly understood. We report a case of an intraneural ganglion arising from the pisotriquetral joint that penetrated the ulnar nerve at Guyon's canal. Although rare, these ganglions should be considered in the differential diagnosis of any neoplasms causing compression neuropathy.

Tibial intraneural ganglia at the ankle and knee: incorporating the unified (articular) theory in adults and children

OBJECT

The etiology of intraneural ganglia has been debated for centuries, and only recently a unifying theory has been proposed. The incidence of tibial nerve intraneural ganglia is restricted to the occasional case report, and there are no reported cases of these lesions in children. While evidence of the unifying theory for intraneural ganglia of the common peroneal nerve is strong, there are only a few reports describing the application of the theory in the tibial nerve. In this report the authors examine tibial nerve intraneural ganglia at the ankle and knee in an adult and a child, respectively, and describe the clinical utility of incorporating the unifying (articular) theory in the management of tibial intraneural ganglia in adults and children.

METHODS

Cases of tibial intraneural ganglion cysts were examined clinically, radiologically, operatively, and histologically to demonstrate the application of the unified (articular) theory for the development of these cysts in adults and children.

RESULTS

Two patients with intraneural ganglion cysts of the tibial nerve were identified: an adult with an intraneural ganglion cyst of the tibial nerve at the tarsal tunnel and a child with an intraneural ganglion cyst of the tibial nerve at the knee. In each case, preoperative MR imaging demonstrated the intraneural cyst and its connection to the adjacent joint via the articular branch to the subtalar joint and superior tibiofibular joint. At surgery the articular branch was identified and resected, thus disconnecting the tibial nerve intraneural cyst from the joint of origin.

CONCLUSIONS

These cases detail the important features of intraneural ganglion cysts of the tibial nerve and document the clinical utility of incorporating the unifying (articular) theory for the surgical management of tibial intraneural ganglia in adults and children.

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

Intraneural ganglion cysts have been considered a curiosity for 2 centuries. Based on a unifying articular (synovial) theory, recent evidence has provided a logical explanation for their formation and propagation. The fundamental principle is that of a joint origin and a capsular defect through which synovial fluid escapes following the articular branch, typically into the parent nerve. A stereotypical, reproducible appearance has been characterized that suggests a shared pathogenesis. In the present report the authors will provide a mechanistic explanation that can then be mathematically tested using a preliminary model created by finite element analysis.

Sciatic cross-over in patients with peroneal and tibial intraneural ganglia confirmed by knee MR arthrography

BACKGROUND

A 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 FINDINGS

One 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.

CONCLUSIONS

This 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.

The clock face guide to peroneal intraneural ganglia: critical "times" and sites for accurate diagnosis

OBJECTIVE

The aim of this study is to exploit the normal nature of peroneal nerve anatomy to identify constant magnetic resonance imaging (MRI) patterns in peroneal intraneural ganglia.

DESIGN

This study is designed as a retrospective clinical study.

MATERIALS AND METHODS

MR images of 25 patients with peroneal intraneural ganglia were analyzed and were compared to those of 25 patients with extraneural ganglia and 25 individuals with normal knees. All specimens were interpreted as left-sided. Using conventional axial images, the position of the common peroneal nerve and either intraneural or extraneural cyst was determined relative to the proximal fibula and the superior tibiofibular joint using a symbolic clock face. In all patients, the common peroneal nerve could be seen between the 4 and 5 o'clock position at the mid-portion of the fibular head. In patients with intraneural ganglia, a single axial image could reproducibly and reliably demonstrate both cyst within the common peroneal nerve at the mid-portion of the fibular head (signet ring sign) between 4 and 5 o'clock and within the articular branch at the superior tibiofibular joint connection (tail sign) between 11 and 12 o'clock; in addition, cyst within the transverse limb of the articular branch (transverse limb sign) was seen at the mid-portion of the fibular neck between the 12 and 2 o'clock positions on serial images. Extraneural ganglia typically arose from more superior joint connections with the epicenter of the cyst varying around the entire clock face without a consistent pattern. There was no significant difference between the visual and template assessment of clock face position for all three groups (intraneural, extraneural, and controls). We believe that the normal anatomic and pathologic relationships of the common peroneal nerve in the vicinity of the fibular neck/head region can be established readily and reliably on single axial images. This technique can provide radiologists and surgeons with rapid and reproducible information for diagnosis and treatment planning.

CONCLUSIONS

By using conventional bony anatomy as reference points (namely fibular neck and mid-portion of fibular head), standard axial images can be used to interpret key features of peroneal intraneural ganglia and to establish their accurate diagnosis (rather than extraneural ganglia) and pathogenesis from an articular origin (rather than from de novo formation), a fact that has important therapeutic implications. Because of the relative rarity of peroneal intraneural cysts and physicians' (radiologists and surgeons) inexperience with them and the complexity of their findings, they are frequently misdiagnosed and joint communications are not appreciated preoperatively or intraoperatively. As a result, outcomes are suboptimal and recurrences are common.

Patterns of intraneural ganglion cyst descent

On the basis of the principles of the unifying articular theory, predictable patterns of proximal ascent have been described for fibular (peroneal) and tibial intraneural ganglion cysts in the knee region. The mechanism underlying distal descent into the terminal branches of the fibular and tibial nerves has not been previously elucidated. The purpose of this study was to demonstrate if and when cyst descent distal to the articular branch-joint connection occurs in intraneural ganglion cysts to understand directionality of intraneural cyst propagation. In Part I, the clinical records and MRIs of 20 consecutive patients treated at our institution for intraneural ganglion cysts (18 fibular and two tibial) arising from the superior tibiofibular joint were retrospectively analyzed. These patients underwent cyst decompression and disconnection of the articular branch. Five of these patients developed symptomatic cyst recurrence after cyst decompression without articular branch disconnection which was done elsewhere prior to our intervention. In Part II, five additional patients with intraneural ganglion cysts (three fibular and two tibial) treated at other institutions without disconnection of the articular branch were compared. These patients in Parts I and II demonstrated ascent of intraneural cyst to differing degrees (12 had evidence of sciatic nerve cross-over). In addition, all of these patients demonstrated previously unrecognized MRI evidence of intraneural cyst extending distally below the level of the articular branch to the joint of origin: cyst within the proximal most portions of the deep fibular and superficial fibular branches in fibular intraneural ganglion cysts and descending tibial branches in tibial intraneural ganglion cysts. The patients in Part I had complete resolution of their cysts at follow-up MRI examination 1 year postoperatively. The patients in Part II had intraneural recurrences postoperatively within the articular branch, the parent nerve, and the terminal branches, although in three cases they were subclinical. The authors demonstrate that cyst descent distal to the take-off of the articular branch to the joint of origin occurs regularly in patients with fibular and tibial intraneural ganglion cysts. The authors believe that parent terminal branch descent follows ascent up the articular branch from an affected joint of origin. This mechanism for bidirectional flow explains cyst within terminal branches of the fibular and tibial nerves and is dependent on pressure fluxes and resistances. This new pattern is consistent with principles previously described in a unified (articular) theory, is generalizable to other intraneural ganglion cysts arising from joints, and has important implications for pathogenesis and treatment of these intraneural cysts.

Cross-over: a generalizable phenomenon necessary for secondary intraneural ganglion cyst formation

The appearances of intraneural ganglion cysts are being elucidated. We previously introduced the cross-over phenomenon to explain how a fibular (peroneal) or tibial intraneural ganglion cyst arising from the superior tibiofibular joint could give rise to multiple cysts: 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 or descent down the same parent nerve or the opposite, previously unaffected fibular or tibial nerves. In this study, we hypothesized that cross-over could occur in other nerves, potentially leading to the formation of more than one intraneural ganglion cyst in such situations. We analyzed the literature and identified a single case that we could review where proximal extension of an intraneural ganglion cyst involving a nerve at a different site could theoretically undergo cross-over in another major nerve large enough for available magnetic resonance images to resolve this finding. A case of a suprascapular intraneural ganglion cyst previously reported by our group that arose from the glenohumeral joint and extended to the neck was reanalyzed for the presence or absence of cross-over. An injection of dye into the outer epineurium of the suprascapular nerve in a fresh cadaveric specimen was performed to test for cross-over experimentally. Retrospective review of this case of suprascapular intraneural ganglion cyst demonstrated evidence to support previously unrecognized cross-over at the level of the upper trunk, with predominant ascent up the C5 and the C6 nerve roots and subtle descent down the anterior and posterior divisions of the upper trunk as well as the proximal portion of the suprascapular nerve. This appearance gave rise to multiple interconnected intraneural ganglion cysts arising from a single distant connection to the glenohumeral joint. The injection study also demonstrated the cross-over phenomenon and produced a similar pattern as the cyst dissection. This article illustrates that cross-over can occur in another nerve (apart from the prototype fibular nerve). Furthermore, understanding the more complex anatomic nature of the upper trunk cross-over model provides insight into important mechanistic information regarding the bidirectional propagation patterns and formation of primary and secondary intraneural ganglion cysts not afforded by the previously described sciatic nerve cross-over model.

Sequential tibial and peroneal intraneural ganglia arising from the superior tibiofibular joint

We present a patient who developed a peroneal intraneural ganglion and an adventitial cyst following the incomplete treatment of a tibial intraneural ganglion. These separate cysts all originated from the superior tibiofibular joint and dissected along their respective articular branches. A logical mechanistic explanation for these coexisting cysts is provided, which highlights the shared pathogenesis--its joint-related nature--rather than a multifocal de novo process. These observations would not only be consistent with, but would extend previous evidence in support of, the unifying articular (synovial) theory.

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

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.

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

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.