The nearly invisible intraneural cyst: a new and emerging part of the spectrum.

OBJECTIVE The authors have observed that a subset of patients referred for evaluation of peroneal neuropathy with "negative" findings on MRI of the knee have subtle evidence of a peroneal intraneural ganglion cyst on subsequent closer inspection. The objective of this study was to introduce the nearly invisible peroneal intraneural ganglion cyst and provide illustrative cases. The authors further wanted to identify clues to the presence of a nearly invisible cyst. METHODS Illustrative cases demonstrating nearly invisible peroneal intraneural ganglion cysts were retrospectively reviewed and are presented. Case history and physical examination, imaging, and intraoperative findings were reviewed for each case. The outcomes of interest were the size and configuration of peroneal intraneural ganglion cysts over time, relative to various interventions that were performed, and in relation to physical examination and electrodiagnostic findings. RESULTS The authors present a series of cases that highlight the dynamic nature of peroneal intraneural ganglion cysts and introduce the nearly invisible cyst as a new and emerging part of the spectrum. The cases demonstrate changes in size and morphology over time of both the intraneural and extraneural compartments of these cysts. Despite "negative" MR imaging findings, nearly invisible cysts can be identified in a subset of patients. CONCLUSIONS The authors demonstrate here that peroneal intraneural ganglion cysts ride a roller coaster of change in both size and morphology over time, and they describe the nearly invisible cyst as one end of the spectrum. They identified clues to the presence of a nearly invisible cyst, including deep peroneal predominant symptoms, fluctuating symptoms, denervation changes in the tibialis anterior muscle, and abnormalities of the superior tibiofibular joint, and they correlate the subtle imaging findings to the internal fascicular topography of the common peroneal nerve. The description of the nearly invisible cyst may allow for increased recognition of this pathological entity that occurs with a spectrum of findings.

Recognition of peroneal intraneural ganglia in an historical cohort with "negative" MRIs.

BACKGROUND: The objective of this study was to review an historical cohort of patients with peroneal neuropathy and magnetic resonance imaging (MRI) read as negative for mass or cyst to determine if occult peroneal intraneural ganglion cysts can be identified on subsequent imaging review and to use this as an estimation of how under-recognized this pathologic entity is. METHOD: The patient cohort utilized in this study was a previously published control cohort of 11 patients with peroneal neuropathy and MRI read as negative for mass or cyst. Clinical history, neurologic examination, and MRI studies of the knee were reviewed for each of the included patients. The primary outcome of interest was the presence of peroneal intraneural ganglion cyst on MRI. RESULTS: Overall, 7 of 11 (64%) patients in this historical "normal" cohort had evidence of a peroneal intraneural ganglion cyst on subsequent review of imaging. Deep peroneal-predominant weakness, knee pain, and tibialis anterior-predominant denervation/atrophy were seen more commonly in patients in whom an intraneural cyst was identified. CONCLUSIONS: This retrospective cohort study provides evidence that peroneal intraneural ganglion cysts are an historically under-recognized cause of peroneal neuropathy, with 64% of this historical "negative" cohort having evidence of a cyst on subsequent imaging review. Larger studies are needed to determine the treatment ramifications of identifying small cysts and to determine the clinical features suggestive of an intraneural ganglion cyst.

Tumefactive appearance of peripheral nerve involvement in hematologic malignancies: a new imaging association.

OBJECTIVE: In neurolymphomatosis (NL), the affected nerves are typically described to be enlarged and hyperintense on T2W MR sequences and to avidly enhance on gadolinium-enhanced T1WI. This pattern is highly non-specific. We recently became aware of a "tumefactive pattern" of NL, neuroleukemiosis (NLK) and neuroplasmacytoma (NPLC), which we believe is exclusive to hematologic diseases affecting peripheral nerves. MATERIALS AND METHODS: We defined a "tumefactive" appearance as complex, fusiform, hyperintense on T2WI, circumferential tumor masses encasing the involved peripheral nerves. The nerves appear to be infiltrated by the tumor. Both structures show varying levels of homogenous enhancement. We reviewed our series of 52 cases of NL in search of this pattern; two extra outside cases of NL, three cases of NLK, and one case of NPLC were added to the series. RESULTS: We identified 20 tumefactive lesions in 18 patients (14 NL, three NLK, one NPLC). The brachial plexus (n = 7) was most commonly affected, followed by the sciatic nerve (n = 6) and lumbosacral plexus (n = 3). Four patients had involvement of other nerves. All were proven by biopsy: the diagnosis was high-grade lymphoma (n = 12), low-grade lymphoma (n = 3), acute leukemia (n = 2), and plasmacytoma (n = 1). CONCLUSIONS: We present a new imaging pattern of "tumefactive" neurolymphomatosis, neuroleukemiosis, or neuroplasmacytoma in a series of 18 cases. We believe this pattern is associated with hematologic diseases directly involving the peripheral nerves. Knowledge of this association can provide a clue to clinicians in establishing the correct diagnosis. Bearing in mind that tumefactive NL, NLK, and NPLC is a newly introduced imaging pattern, we still recommend to biopsy patients with suspicion of a malignancy.

Hilton's law revisited.

Hilton's Law, put forth 150 years ago, is well known and frequently taught in anatomy courses. We critically analyzed the complex description of associated muscular, cutaneous, and articular innervations in order to assess the general applicability of Hilton's Law. We applied rules for interpretation of the Law extrapolated upon but based on Hilton's original writings, and excluded obscure supplementary clauses not considered as part of the Law. We found the Law, as originally written and as we interpreted with some latitude, to be reliable and applicable to all cranial and peripheral nerves. Hilton's Law is a powerful springboard to understand articular anatomy and pathophysiology.

Core outcomes in nerve surgery: development of a core outcome set for ulnar neuropathy at the elbow.

OBJECTIVE: Ulnar neuropathy at the elbow (UNE) is common, affecting 1%-6% of the population. Despite this, there remains a lack of consensus regarding optimal treatment. This is primarily due to the difficulty one encounters when trying to assess the literature. Outcomes are inconsistently reported, which makes comparing studies or developing meta-analyses difficult or even impossible. Thus, there is a need for a core outcome set (COS) for UNE (COS-UNE) to help address this problem. The objective of this study was to utilize a modified Delphi method to develop COS-UNE. METHODS: A 5-stage approach was utilized to develop COS-UNE: stage 1, consortium development; 2, literature review to identify potential outcome measures; 3, Delphi survey to develop consensus on outcomes for inclusion; 4, Delphi survey to develop definitions; and 5, consensus meeting to finalize the COS and definitions. The study followed the Core Outcome Set-STAndards for Development (COS-STAD) recommendations. RESULTS: The Core Outcomes in Nerve Surgery (COINS) Consortium comprised 21 participants, all neurological surgeons representing 11 countries. The final COS-UNE consisted of 22 data points/outcomes covering the domains of demographic characteristics, diagnostics, patient-reported outcomes, motor/sensory outcomes, and complications. Appropriate instruments, methods of testing, and definitions were set. The consensus minimum duration of follow-up was 6 months, with the consensus optimal timepoints for assessment identified as preoperatively and 3, 6, and 12 months postoperatively. CONCLUSIONS: The authors identified consensus data points/outcomes and also provided definitions and specific scales to be utilized to help ensure that clinicians are consistent in their reporting across studies on UNE. This COS should serve as a minimum set of data to be collected in all future neurosurgical studies on UNE. The authors hope that clinicians evaluating ulnar neuropathy will incorporate this COS into routine practice and that future studies will consider this COS in the design phase.

Neurological outcome following resection of benign presacral neurogenic tumors using a nerve-sparing technique.

BACKGROUND: Benign presacral nerve sheath tumors represent up to 10% of all presacral tumors. Limited data exist regarding the impact of the surgical technique on neurological outcomes following resection. OBJECTIVE: The aim of this study was to test our hypothesis that a nerve-sparing resection technique results in the improvement of preoperative neurological dysfunction and minimal postoperative neurological morbidity. DESIGN: This study is a case series of all patients with benign neurogenic presacral tumors operated on by the same 2 surgeons between 2004 and 2010 at our institution. SETTINGS: This study was performed at a tertiary care center. PATIENTS: Adult patients with benign presacral neurogenic tumors who underwent a nerve-sparing resection were included. MAIN OUTCOME MEASURES: Postoperative urogenital, anorectal, and lower-extremity neurological functions were analyzed. RESULTS: Seventeen patients were identified with a mean age of 40 years; 14 were women. Preoperatively, 13 patients had symptoms from neurological dysfunction or presumed mass effect of the tumor. The mean tumor size was 7.4 cm. The pathology was a schwannoma in 12 patients and neurofibroma in 5 patients. Mortality was nil, and 30-day morbidity was noted in 3 patients (hemorrhage, ileus, acute respiratory distress syndrome, deep vein thrombosis, and transient foot drop). Mean follow-up was 36 months. Of the 13 symptomatic patients, 7 achieved complete resolution of symptoms and 5 had improved, but persistent symptoms. None of the 4 asymptomatic patients developed postoperative neurological dysfunction. LIMITATIONS: Small sample size was a limitation of this study. CONCLUSIONS: With the use of a nerve-sparing technique, function-preserving resection can be safely completed with an overall improvement in symptoms.

Lateral Displacement of the Phrenic Nerve in C5 Tumors.

BACKGROUND AND OBJECTIVES: Nerve sheath tumors of the brachial plexus frequently distort the local anatomy, increasing the difficulty of safe exposure and resection. However, lateral displacement of the phrenic nerve has not been previously described. The purpose of this study was thus to illustrate the abnormal lateral displacement of the phrenic nerve in 2 cases of patients undergoing brachial plexus tumor resection and provide a possible mechanism for this observation. METHODS: Two patients underwent surgical resection of clinically progressing C5 schwannomas. During exposure, the phrenic nerve was found to be significantly more superficial and lateral than typical. This structural relationship persisted even after complete resection of the lesion. Both patients did well postoperatively. RESULTS: The phrenic nerve traverses along the anterolateral aspect of the anterior scalene. However, in these 2 cases of C5 nerve sheath tumors, the phrenic was found to be significantly more lateral and superficial than usual, draping across the medial aspect of the tumor. We believe that the C5-phrenic communicating branch may act as a functional tether that mobilizes the phrenic nerve laterally as the tumor grows. The mass effect on the anterior scalene by the underlying C5 tumor may further contribute to the anterolateral and superficial displacement of the nerve. CONCLUSION: The phrenic nerve may be seen markedly more laterally and superficially displaced in cases of C5 nerve sheath tumors. It is important for surgeons who operate on lesions of the brachial plexus to be aware of this phenomenon.

Rat sciatic nerve repair with a poly-lactic-co-glycolic acid scaffold and nerve growth factor releasing microspheres.

The effect of microsphere delivered Nerve Growth Factor (NGF) in a poly-lactic-co-glycolic-acid (PLGA) 85/15 nerve conduit bridging a 10mm rat sciatic nerve gap was assessed, comparing nine groups (n = 6): PLGA conduits filled with saline, saline and NGF, saline with blank microspheres; four different NGF microspheres (5, 20, 50, and 100 mg/ml); an autologous graft and sciatic nerve gap. Histomorphometry, retrograde tracing, electrophysiology, and functional outcomes were evaluated up to 16 weeks. The autologous graft showed the largest fascicular area (0.65 mm(2) ) and had a significantly greater number of myelinated fibers (P < 0.0001). Electrophysiology showed Compound Muscle Action Potential (CMAP) recordings for the autologous graft returning at 6 weeks after nerve transection, reaching their highest amplitude of 3.6 mV at endpoint. No significant differences were found in functional evaluation between groups or between conduits with microspheres and the saline filled conduit. A PLGA 85/15 nerve conduit is capable of sustaining nerve regeneration. The microsphere delivery system does not interfere with regeneration.

An anatomically based imaging sign to detect adventitial cyst derived from the superior tibiofibular joint.

The origin for complex intraneural cysts remains controversial despite recent emerging evidence to support their articular origin. The coexistence of intraneural and adventitial cysts has been described due to the proximate neurovascular bundle, i.e., the articular (neural) branch and vessels at the joint capsule. To clarify the pathogenesis, anatomically based imaging patterns can be identified. This paper characterizes a common finding identified on MRI describing the adventitial component originating from the superior tibiofibular joint (STFJ). MRIs of patients with fibular (peroneal) (n = 24) and tibial (n = 7) intraneural ganglion cysts were reviewed. Eleven patients with fibular intraneural ganglion cysts were identified as having a coexisting adventitial component. In all cases, the adventitial cyst extended from the anterior portion of the STFJ, within the capsular vessels, and along the anterior tibial vessels. The reproducible anatomy permitted the identification of an imaging pattern: the "vascular U" sign, consisting of cystic anterior tibial vessels running through the interosseous membrane between the proximal tibia and fibula. This sign was seen on axial MR image(s) obtained at the level of the fibular neck in all cases. To generalize these findings, the rare tibial intraneural ganglion cysts (derived from the posterior aspect of the STFJ) were examined; two cases had coexisting adventitial cysts with visualization of the vascular U sign. This new imaging pattern can improve the identification of adventitial cysts at the level of the STFJ.

Extraneural rupture of intraneural ganglion cysts.

Rupture of simple (extraneural) cysts such as popliteal cysts (Baker's cysts) is a well-known occurrence. The purpose of this report is to introduce the similar occurrence of extraneural rupture of peroneal and tibial intraneural cysts in the knee region, describe the associated magnetic resonance imaging (MRI) findings, and identify risk factors. There was MRI evidence of rupture in 20 of 38 intraneural cases reviewed, mainly in the region of the fibular head and popliteal fossa. Ruptured intraneural cysts and simple cysts share these MRI findings: T2 hyperintense fluid within surrounding intermuscular fascial planes and enhancement with intravenous contrast consistent with inflammation. The mean maximal diameter of the ruptured intraneural cysts was statistically significantly smaller than that of the unruptured cysts. The authors believe that extraneural rupture of an intraneural cyst is due to increased intraarticular pressures transmitted within the cyst and/or elevated extrinsic pressure delivered to the cyst, such as by trauma, akin to the etiology of rupture of extraneural ganglion cysts.

Endoscopic third ventriculostomy for VP shunt malfunction during the third trimester of pregnancy: illustrative case.

BACKGROUND: Endoscopic third ventriculostomy (ETV) is a successful procedure for treating noncommunicating hydrocephalus as an alternative to initial ventriculoperitoneal (VP) shunt placement and as a salvage procedure when a VP shunt fails. Physiological changes of pregnancy can lead to VP shunt failure and complicate the management of shunt malfunction, particularly in the third trimester. OBSERVATIONS: The authors present a case in which an ETV was successfully used in the third trimester (31 weeks of gestation) of pregnancy for acute hydrocephalus due to VP shunt malfunction, and the patient went on to deliver a healthy baby at term; the patient remained well in the long-term follow-up. An English-language PubMed literature review revealed four cases of VP shunt failure successfully treated with an ETV in the first or second trimester but no such reports in the third trimester of pregnancy. LESSONS: ETV appears to be a safe and effective alternative to VP shunt replacement in the late prenatal period of pregnancy.

Tibialis anterior branch involvement in fibular intraneural ganglia.

Fibular (peroneal) intraneural ganglia classically present with predominant tibialis anterior weakness, for which there is no clear anatomical explanation. We identified a new imaging pattern, which consisted of involvement of a proximal tibialis anterior branch, in patients with fibular intraneural ganglia. This study characterizes the cystic involvement of this tibialis anterior branch and evaluates its significance. The magnetic resonance imaging (MRI) and clinical data of 23 patients with fibular intraneural ganglia were retrospectively reviewed. The tibialis anterior branch was consistently involved with the cyst, and this involvement, although variable, was more prominent than the cystic involvement of other terminal branches of the fibular nerve. The finding of cyst extension within a muscle end-organ branch seems likely to explain, in part, the characteristic clinical finding of preferential foot drop in patients with fibular intraneural ganglia.

Adenocarcinoma of the prostate involving the lumbosacral plexus: MRI evidence to support direct perineural spread.

BACKGROUND: Prostate adenocarcinoma, which may recur despite aggressive treatment, has the potential to spread to the lumbosacral plexus. This intraneural involvement is not widely known and is thought to be from direct perineural spread. We hypothesized that high-resolution imaging could provide supportive evidence for this mechanism. METHODS: The clinical data and imaging studies (magnetic resonance imaging, MRI, and positron emission tomography/computed tomography, PET/CT) of patients evaluated at our institution between 2004 and 2009 for lumbosacral plexopathy due to intraneural prostate carcinoma were retrospectively reviewed. RESULTS: Four patients presenting with painful lumbosacral plexopathy were found to have intraneural lumbosacral prostate adenocarcinoma. Two patients had involvement of the lumbosacral plexus ipsilateral to the lobe of the prostate most involved with adenocarcinoma at prostatectomy. High-resolution MRI and PET/CT studies revealed similar findings: abnormal soft tissue signal was followed from the prostate (n = 1) or prostatic bed (n = 3) area along the expected course of the pelvic plexus to the level of the sciatic notch, where it involved the sacral spinal nerves and sciatic nerve. Imaging findings were consistent with neoplastic infiltration, which was confirmed at biopsy in three patients. CONCLUSIONS: The potential for prostate adenocarcinoma to spread to the lumbosacral plexus has, to our knowledge, not been readily appreciated. Because the imaging findings are often subtle, we believe that intraneural lumbosacral plexus involvement may not be uncommon. This study, with the use of high-resolution MRI and PET/CT studies, supports the direct perineural spread of prostate adenocarcinoma via the pelvic plexus to the lumbosacral plexus. This mechanism could also explain cases of leptomeningeal and/or dural-based prostate metastases.

The normal and pathologic MRI appearance of the tibialis anterior proximal motor branch.

Foot drop, the clinical manifestation of tibialis anterior (TA) muscle dysfunction, may be caused by pathologies involving selectively the TA motor nerve branches. Recently, in patients with fibular intraneural ganglion cysts, cystic involvement of the TA motor branch from the articular branch was demonstrated. However, no imaging characteristics of this functionally important TA proximal motor branch have been reported. We hypothesized that this particular TA proximal motor branch could be visualized and characterized on high-resolution clinical magnetic resonance imaging (MRI) in both normal and pathologic cases. Twenty-six consecutive high-resolution knee MRI examinations performed for routine indications such as exclusion of intra-articular pathology and four illustrative cases imaged to evaluate pathology of the common fibular nerve and its branches (specifically the TA proximal motor branch) were retrospectively reviewed. In cases without fibular nerve pathology, the TA proximal motor branch was visualized in 21 of the 26 patients. In the cases in which the nerve was not visualized, the imaging techniques could explain the nonvisualization of the branch. The involvement of the proximal branch to the TA was evident in the four patients with pathology, which included a perineurioma, a fibular intraneural ganglion cyst, a plexiform neurofibroma, and an inflammation of the nerve. In both normal and pathologic cases, the functionally important TA proximal motor branch originating from the articular branch can be consistently visualized on high-resolution MRI. This branch can be selectively affected by a variety of pathologies and its identification on imaging may help elucidate the predominant TA muscle involvement in these patients.

A complex cyst characterized into its individual components: a shared pathogenesis from the superior tibiofibular joint.

In a patient with a peroneal neuropathy, magnetic resonance imaging (MRI) allowed characterization of a complex para-articular cyst into three different types of cysts, all derived from the superior tibiofibular joint: 1) an intraneural cyst extending along the articular branch to the common peroneal nerve; an interconnected intraneural component extending within the extensor digitorum muscle neural branch, penetrating the fascia of the anterior compartment, and reaching the subcutaneous tissues; 2) an intraosseous cyst isolated to the fibular head and neck, and 3) an extraneural cyst heading toward the tibial nerve and vessels. Joint resection and articular branch disconnection led to excellent functional recovery; an MRI confirmed no cyst recurrence. This case illustrates that different types of cysts can derive from a single joint of origin and extend in various locations and that the articular (synovial) theory is versatile for demonstrating a joint connection, even in unusual appearing combinations of cysts.

Understanding the Pathognomonic Tumefactive Appearance of Neurolymphomatosis: A Unifying Theory of Neurolymphoma.

BACKGROUND: The diagnosis of peripheral neurolymphomatosis (NL) is difficult and often delayed, because patients can have isolated, nonspecific nerve symptoms. Magnetic resonance imaging will usually show nonspecific findings of enlarged, contrast-enhancing nerves. We aimed to elucidate the mechanism behind an imaging finding we believe is pathognomonic of NL and likely of other hematologic diseases with peripheral nerve involvement. METHODS: We reviewed the imaging studies of a previously reported cohort of patients, in addition to those from more recent patients, all with tumefactive NL, in which enlarged nerve bundles were surrounded by tumor. We reviewed the demographic data, clinical data (e.g., primary or secondary disease, biopsy-proven diagnosis), and imaging findings (e.g., tumefactive appearance, primary involved nerve, location of epicenter of tumefactive appearance, vascular involvement). RESULTS: All cases showed a maximum tumefactive appearance at branch or junction points, with a gradual decrease of this appearance moving proximally and distally from the epicenter in a "crescendo-decrescendo" pattern. We have described this as a phasic mechanism with 3 phases: malignant cells fill the intraneural space; extrude at a weak spot of the nerve, which often occurs at a branch or junction point; and then expand and fill the subparaneurial space, creating the grossly tumefactive appearance with proximal and distal spread. CONCLUSIONS: We have presented a novel, unifying theory explaining the pathognomonic tumefactive appearance of NL. Our theory offers the first rational explanation for the radiological appearance of NL with peripheral nerve involvement. We believe that with earlier recognition of NL on imaging studies, patients will be able to receive an earlier diagnosis and undergo earlier treatment.

DGCR8 microprocessor defect characterizes familial multinodular goiter with schwannomatosis.

BACKGROUNDDICER1 is the only miRNA biogenesis component associated with an inherited tumor syndrome, featuring multinodular goiter (MNG) and rare pediatric-onset lesions. Other susceptibility genes for familial forms of MNG likely exist.METHODSWhole-exome sequencing of a kindred with early-onset MNG and schwannomatosis was followed by investigation of germline pathogenic variants that fully segregated with the disease. Genome-wide analyses were performed on 13 tissue samples from familial and nonfamilial DGCR8-E518K-positive tumors, including MNG, schwannomas, papillary thyroid cancers (PTCs), and Wilms tumors. miRNA profiles of 4 tissue types were compared, and sequencing of miRNA, pre-miRNA, and mRNA was performed in a subset of 9 schwannomas, 4 of which harbor DGCR8-E518K.RESULTSWe identified c.1552G>A;p.E518K in DGCR8, a microprocessor component located in 22q, in the kindred. The variant identified is a somatic hotspot in Wilms tumors and has been identified in 2 PTCs. Copy number loss of chromosome 22q, leading to loss of heterozygosity at the DGCR8 locus, was found in all 13 samples harboring c.1552G>A;p.E518K. miRNA profiling of PTCs, MNG, schwannomas, and Wilms tumors revealed a common profile among E518K hemizygous tumors. In vitro cleavage demonstrated improper processing of pre-miRNA by DGCR8-E518K. MicroRNA and RNA profiling show that this variant disrupts precursor microRNA production, impacting populations of canonical microRNAs and mirtrons.CONCLUSIONWe identified DGCR8 as the cause of an unreported autosomal dominant mendelian tumor susceptibility syndrome: familial multinodular goiter with schwannomatosis.FUNDINGCanadian Institutes of Health Research, Compute Canada, Alex's Lemonade Stand Foundation, the Mia Neri Foundation for Childhood Cancer, Cassa di Sovvenzioni e Risparmio fra il Personale della Banca d'Italia, and the KinderKrebsInitiative Buchholz/Holm-Seppensen.

Intraneural ganglia in the hip and pelvic region. Clinical article.

OBJECT: The authors describe their experience in a series of cases of intraneural ganglia within the hip and pelvic regions, and explain the mechanism of formation and propagation of this pathological entity. METHODS: Five patients with 6 intraneural ganglia are presented. Four patients presented with symptomatic intraneural ganglia in the buttock and pelvis affecting the sciatic and lumbosacral plexus elements. An asymptomatic cyst affecting the opposite sciatic nerve was found on MR imaging in 1 patient. The fifth patient, previously reported on by another group, had an obturator intraneural ganglion that the authors reinterpreted. RESULTS: All 5 intraneural ganglia affecting the sciatic and lumbosacral plexus elements were found to have a joint connection to the posteromedial aspect of the hip joint; the obturator intraneural cyst had a joint connection to the anteromedial aspect of the hip joint. In all cases, initial review of the MR images led to their misinterpretation. CONCLUSIONS: To the authors' knowledge, these are the first cases of intraneural ganglia demonstrated to have a connection to the hip joint. This finding at a rare site provides further evidence for the unifying articular (synovial) theory for the formation of intraneural ganglia and reveals a shared mechanism for their propagation. Furthermore, understanding the pathogenesis of these lesions provides insight into their successful treatment and their recurrence.

Clock face model applied to tibial intraneural ganglia in the popliteal fossa.

BACKGROUND: Tibial intraneural ganglia occurring in the popliteal fossa are often misdiagnosed because of their relative rarity. Their joint connection is typically not recognized and therefore not treated, leading to recurrence. STUDY DESIGN: This is a retrospective clinical study. MATERIALS AND METHODS: Magnetic resonance images (MRIs) of six patients with confirmed tibial intraneural ganglia arising from the superior tibiofibular joint were analyzed and were compared to ten individuals with normal tibial nerves who were imaged with MRI. All studies were interpreted as left-sided. A previously designed clock face model introduced for peroneal intraneural ganglia was used to describe the superior tibiofibular joint connection (tail sign). A single axial image was sought to determine the normal anatomic and pathologic relationships of the tibial nerve and tibial articular branch to the superior tibiofibular joint. RESULTS: In all patients with intraneural ganglia, a single conventional axial image at the mid-fibular head level could reliably demonstrate: (1) intraneural cyst within the articular branch at the superior tibiofibular joint connection (tail sign) between 8 and 9 o'clock and intraneural cyst within the tibial nerve, (2) the central location of the tibial nerve posterior to the tibia, and (3) popliteus muscle denervation changes and atrophy (popliteus sign). CONCLUSIONS: This technique can provide radiologists and surgeons with rapid and reproducible information for diagnosis and treatment planning of tibial intraneural ganglia. Similar to its use with the clock face model in peroneal intraneural ganglia, a standard axial image at the mid-fibular head level can be used to interpret key features of tibial intraneural ganglia and identify the joint connection. Improved identification of the presence of a joint connection will change the therapeutic approach of this pathology and reduce cyst recurrences.

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.