Original Article

Obturator Intraneural Ganglion Cysts: Connected and Underdiagnosed Ekkapot Jitpun1,4, Benjamin (Matthew) M. Howe2, Kimberly K. Amrami2, Robert T. Trousdale3, Robert J. Spinner1

- BACKGROUND: Intraneural ganglion cysts of the obtu- INTRODUCTION rator nerve are rare. Our aim is to review cases of obturator ntraneural ganglion cysts, once believed to be rare entities, intraneural ganglion cysts at our institution and those are increasingly being reported in the literature.1 Based on the reported in the literature. I unified articular (synovial) theory,2 they are benign nonneoplastic mucinous cystic lesions that originate from - METHODS: We reviewed all cases evaluated by the synovial , propagate within the epineurium of small senior author. A literature search was performed using the articular branches innervating the synovial joints, and extend via PubMed database and Google Scholar with the following the path of least resistance to reach the parent nerve. They terms: "obturator cyst," "obturator intraneural ganglion cause predictable symptoms and signs of peripheral neuropathy cyst,” and "obturator intraneural ganglia." All cases un- in the territory of the parent nerves. Intraneural ganglion cysts derwent a retrospective review. Patient demographic data, arising from the hip joint are unusual, especially those involving 3 including age, sex, and presenting signs and symptoms the . We reviewed cases of obturator intraneural were recorded. Imaging studies were re-evaluated by 2 ganglion cysts seen at our institution and in the literature to musculoskeletal radiologists experienced in the diagnosis understand their pathoanatomy and apply these principles to cases of cystic lesions around the hip joint and obturator nerve of intraneural ganglion cysts. reported with alternative diagnoses. - RESULTS: We identified 2 cases of obturator intraneural ganglia at our institution; both were connected to the hip joint. METHODS We found 4 cases that were clearly diagnosed as intraneural We collected all cases evaluated by the senior author (R.J.S). A ganglia in the literature, of which only 1 was recognized by literature search was performed using the PubMed database and the original authors as being joint connected, but based on our Google Scholar. Search terms included “obturator cyst,”“obtu- reinterpretation, 3 of 4 were joint connected. An additional 9 rator intraneural ganglion cyst,” and “obturator intraneural ” cases identified in the literature did not definitely report the ganglia. Cases at our institution and those reported in the liter- nerveecyst relationship, but based on our reinterpretation, ature were reviewed in detail. Patient demographic data, including age, sex, side of the body affected, and presenting symptoms and were believed to be intraneural; 8 were joint connected. signs were recorded. Details of preoperative and postoperative - CONCLUSIONS: We believe that obturator intraneural investigations, including electrodiagnostic and imaging studies, ganglion cysts adhere to the principles of the unifying articular were reviewed. Imaging studies were re-evaluated by 2 fellowship- theory. They arise from the anteromedial hip joint and extend trained musculoskeletal radiologists experienced in the diagnosis into an articular branch and can reach the parent obturator of intraneural ganglion cysts (B.M.H. and K.K.A). nerve. Surgery should address the hip disease and/or the RESULTS articular branch connection. Not appreciating the pathoanat- omy of these cysts can lead to persistent or recurrent cysts. We identified 2 cases of obturator nerve intraneural ganglion cysts evaluated by the senior author at our institution (Table 1). Both cysts were connected to an anterior/anterosuperior acetabular

Key words From the Departments of 1Neurologic Surgery, 2Radiology, and 3Orthopedic Surgery, Mayo 4 - Intraneural ganglion cyst Clinic, Rochester, Minnesota, USA; and Department of Neurosurgery, Prasat Neurological - Obturator cyst Institute, Bangkok, Thailand - Obturator nerve To whom correspondence should be addressed: Robert J. Spinner, M.D. - Unified articular theory [E-mail: [email protected]] Citation: World Neurosurg. (2019) 126:e259-e269. Abbreviations and Acronyms https://doi.org/10.1016/j.wneu.2019.02.029 EMG: Electromyography Journal homepage: www.journals.elsevier.com/world-neurosurgery MR: Magnetic resonance MRI: Magnetic resonance imaging Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2019 Elsevier Inc. All rights reserved.

WORLD NEUROSURGERY 126: e259-e269, JUNE 2019 www.journals.elsevier.com/world-neurosurgery e259 KAO IPNE AL. ET JITPUN EKKAPOT e260 www.SCIENCEDIRECT.com Table 1. Summary of Cases with Obturator Intraneural Ganglion Cysts Identified at Our Institution

Gender, Case Age Joint Electromyography/Nerve Procedures and Number (Years) Presenting Symptoms and Signs Preoperative Imaging Connection Conduction Study Findings Outcome

1 Male, 46 2 months of severe pain in left groin Plain film: cam morphology of the hips Yes Severe left obturator Repair labral tear and At 4-month postoperative follow- and medial with mild degenerative changes mononeuropathy debride chondral defect with up an offset procedure at the Improvement of adductor strength Severe weakness of adduction of left Magnetic resonance imaging: a head and neck junction (Medical Research Council grade thigh with no sensory loss multiloculated ganglion cyst intimately The obturator nerve and the 4) associated with the left obturator nerve cyst were not exposed Pain was minimal measured Electromyography showed 4.3 Â 2.5 Â 1.9 cm significant improvement and A Tinel sign was present in the groin. There was an associated defect of the evidence of ongoing reinnervation inferior joint capsule, complex tearing of of the left adductor longus muscle the superior acetabular labrum and Magnetic resonance imaging at 4 OL NEUROSURGERY WORLD increased signal within the hip adductor months postoperatively showed muscles representing subacute complete resolution of the cyst denervation change. 2 Female, 59 2 years of severe right medial groin Plain film: mild hip and sacroiliac joints Yes Chronic right obturator Procedure performed at an Pain free after operation pain that radiated to medial thigh degenerative changes neuropathy, no evidence of outside institution: anterior after hernia repair lumbar radiculopathy retroperitoneal approach to right showed a dense lipomatous mass firmly attached to L3 nerve root. Debulking of the mass and L3 neurolysis was , https://doi.org/10.1016/j.wneu.2019.02.029 performed CYSTS GANGLION INTRANEURAL OBTURATOR Normal motor and sensory Magnetic resonance imaging: T2 examination hyperintensity lesion followed the course of obturator nerve from obturator canal up to pelvic brim with sausage-like enlargement (6.5 Â 0.8 cm), no gadolinium enhancement No palpable mass Initially believed to be a neurofibroma Pathology: dense fibrous (reinterpreted by our senior author to be connective tissue and an obturator intraneural ganglion cyst) fibroadipose tissue and minute fragment of nerve with no evidence of nerve O RIGINAL tumor A RTICLE ORIGINAL ARTICLE EKKAPOT JITPUN ET AL. OBTURATOR INTRANEURAL GANGLION CYSTS

Figure 1. Case illustration 1. (A) Axial T2-weighted fast the cyst as well as the defect in the joint capsule spin echo magnetic resonance (MR) image with fat (arrow). Note increased T2 signal in the muscle suppression shows the obturator intraneural cyst (asterisk), indicating subacute denervation. (D) Axial (arrow) within the obturator foramen. (B) Axial T1-weighted MR image with fat suppression and T2-weighted fast spin echo MR image with fat intra-articular gadolinium obtained after surgical repair suppression inferior to (A) showing the multiloculated of the labrum showing contrast within the joint and intraneural cyst (arrow) and the associated subacute iliopsoas tendon sheath (asterisk). No cyst material or denervation of the adjacent obturator externus muscle intra-articular contrast is seen in the obturator foramen (asterisk). (C) Coronal T2-weighted MR image with fat (arrow). suppression showing the connection from the joint to

labral tear (Figures 1 and 2). These cysts propagated into the was so severe it sometimes awoke him from sleep (visual analog parent obturator nerve in the . Degenerative changes of the scale score 8e9). There was no sensory loss. Examination hip were present in both cases. showed severe weakness of adduction of the left thigh. A Tinel sign was present in the groin. Plain films of the left hip showed Case Illustration 1 cam morphology of the hips with mild degenerative arthritis. A 46-year-old man with a history of HLA-B27 spondyloarthropathy Magnetic resonance (MR) examination of the pelvis and left hip presented with 2 months of pain in the left groin and medial thigh MR arthrography showed a multiloculated ganglion cyst (4.3 Â and progressive weakness of his proximal left leg, especially with 2.5 Â 1.9 cm diameter) involving the obturator nerve. There was walking (Figure 1). The pain did not radiate below the knee and an associated defect of the inferior joint capsule, a complex tear

WORLD NEUROSURGERY 126: e259-e269, JUNE 2019 www.journals.elsevier.com/world-neurosurgery e261 ORIGINAL ARTICLE EKKAPOT JITPUN ET AL. OBTURATOR INTRANEURAL GANGLION CYSTS

Figure 2. Case Illustration 2. (A) Coronal T2-weighted iliac vein (asterisk). (BeD) Sequential sagittal magnetic resonance image with fat suppression T2-weighted magnetic resonance images with fat showing the proximal extension of the obturator suppression showing the cyst arising from the joint and intraneural cyst (arrows). Note the adjacent common extending along the obturator nerve (arrows).

of the superior and anterosuperior acetabular labrum, diffuse showed significant improvement and evidence of ongoing rein- chondromalacia of the hip, and increased T2-weighted signal nervation of the left adductor longus muscle. MR imaging (MRI) within the hip adductor muscles, representing subacute denerva- showed complete resolution of the cyst. Hip arthrography showed tion change. Electromyography (EMG) showed a severe left that the intra-articular contrast did not extend into the obturator obturator mononeuropathy. nerve. At 1 year follow-up, the patient had minimal pain down the The left hip was exposed via a lateral incision. The joint was leg and minimal adductor dysfunction. MRI showed no evidence opened and the hip was dislocated. A labral tear was repaired and of cyst recurrence. 2-cm  1-cm chondral defect was debrided. An offset procedure at the femoral head and neck junction was performed. The obturator Case Illustration 2 nerve and the cyst were not exposed. At 2 months postoperative A 59-year-old woman presented with a history of right anterior groin follow-up, the patient’s thigh pain was significantly diminished pain after hernia repair (Figure 2). The pain radiated down the (visual analog scale score 2e3) and there was a trace of adduction. anterior and medial aspect of thigh toward the knee. The pain was Postoperative EMG showed evidence of minimal reinnervation of so severe that the patient could not even stand or walk and it also the adductor longus. At 4 months postoperative follow-up, the affected her sleep. Examination showed that there was no patient had considerable improvement of his adductor strength particular hip maneuver or position that reproduced the pain. No (Medical Research Council grade 4). His pain was minimal. EMG mass was palpable. Her motor power and sensation were intact.

e262 www.SCIENCEDIRECT.com WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2019.02.029 KAO IPNE AL. ET JITPUN EKKAPOT OL NEUROSURGERY WORLD

Table 2. Summary of Reported Obturator Intraneural Ganglion Cysts in the Literature

Joint Connection Electromyography/ Gender, Age Presenting Preoperative Data from Original Nerve Conduction Procedures and Reference (Years) Symptoms Initial Diagnosis Imaging Reports Reinterpretation Study Intraoperative Findings Outcome

Uchida, Male, 71 right leg pain Mucoid pseudocyst MRI, computed N/A Yes N/A Exploration with resection Adduction was 3,9 2:e5-29 J e259-e269, 126: 2006 of obturator nerve tomography, urography, of cyst and obturator impaired and (intraneural) cystography: pelvic cyst, no nerve and vessels; the partial loss of contrast enhancement cyst was visualized to the sensation of right of urinary bladder, inner thigh, pain the mass extended to resolved obturator foramen and completely could not be freed from

UNE right obturator nerve 2019 Kitagawa, Male, 31 Weakness of Intraneural ganglion N/A N/A N/A Atrophy and Exploration with gross Decreased 3 200910 adductor muscle cyst of obturator denervation of total resection of points in pain with intractable left nerve, intractable obturator-innervated intraneural ganglion cyst; intensity on obturator neuralgia left obturator adductor muscles resection of cyst and visual analog (not improved after neuralgia nerve, proximal nerve scale, no multiple nerve stump was buried into change in gait blocks) and the cyst psoas muscle, distal function, www.journals.elsevier.com/world-neurosurgery recurred after 2 stump was sealed with adductor motor surgical resections coagulation power not reported Sureka, Male, 26 Adductor muscle Intraneural ganglion MRI: multiple small cysts Yes Yes, with N/A N/A N/A 201211,19 weakness with thigh cyst of obturator along the course of right evidence of labral

pain nerve obturator nerve extending tear CYSTS GANGLION INTRANEURAL OBTURATOR along the articular branch to communicate with the ipsilateral anteromedial hip joint with evidence of denervation of adductor muscles Heinem, Female, 24 Severe left groin Intraneural ganglion MRI: multiloculated N/A Yes, with N/A Surgical exploration: N/A 201618 pain that led to cyst of left obturator ganglion cyst of obturator evidence of labral retroperitoneal and immobility and hip nerve nerve that ascended up to tear medial thigh approaches adductor atrophy L4 nerve with cyst decompression,

preserving the obturator O RIGINAL nerve

MRI, magnetic resonance imaging; N/A, not available. e263 A RTICLE KAO IPNE AL. ET JITPUN EKKAPOT e264 Table 3. Summary of Possible Reported Cases Reinterpreted as Obturator Intraneural Ganglion Cysts

Joint Connection www.SCIENCEDIRECT.com Data Gender, from Electromyography Procedures and Age Presenting Preoperative Original /Nerve Conduction Intraoperative Reference (Years) Symptoms Initial Diagnosis Imaging Reports Reinterpretation Study Findings Outcome

Schwabegger, M, 34 Thigh adduction Obturator nerve MRI and ultrasonography N/A N/A Isolated obturator motor Surgical exploration and Motor function improved 20036 weakness, moderate ganglion (details and images not neuropathy decompression of in 4 months adductor muscle provided); ultrasonography- obturator nerve and atrophy, unspecific pain guided biopsy confirmed removal of ganglion; the at pelvic region mucous content of cyst cyst was visualized in obturator foramen, compressing the obturator nerve between the pubic ramus and obturator externus muscle

OL NEUROSURGERY WORLD Campeas, M, 33 Left groin pain radiating Hip joint ganglion cyst Plain film: normal Yes Yes, with N/A Surgical exploration N/A 20037 down the medial thigh that impinged on the MRI: hip joint was normal; a evidence of labral with complete remove to the knee obturator nerve well-circumscribed cystic tear of cyst; obturator nerve mass with fluid signal in the was noticeably deviated lower left pelvis along pelvic by the mass, which was side wall extended through dissected away from the obturator canal the nerve Yukata, F, 75 Right groin and Acetabular labral cyst MRI: a cystic lesion arising Yes Yes, with N/A Ultrasonography-guided Diminished pain after 4 20058,20 anteromedial thigh causing obturator from the anterior aspect of evidence of labral aspiration: yellow thick days of operation and pain, which was nerve entrapment right acetabulum, extending tear gelatinous fluid asymptomatic at 8 months exacerbated in medially into the lateral wall follow-up , https://doi.org/10.1016/j.wneu.2019.02.029 abduction and external of lesser pelvis with signs of CYSTS GANGLION INTRANEURAL OBTURATOR rotation of the hip, no denervation in obturator motor weakness or externus, adductor, and sensory change gracilis muscles Botchu, 20134 F, 67 Dull left buttock and Ganglion arising from MRI: a multiloculated cystic Yes Yes N/A Ultrasound-guided Hip pain had resolved and groin pain aggravated transverse acetabular lesion in the obturator aspiration of the there was no recurrence by weight bearing and foramen ganglion and injection at 1 year follow-up walking. No muscle Magnetic resonance of triamcinolone and weakness arthrography: a ganglion bupivacaine arising from the transverse acetabular ligament without

communication to the hip O joint RIGINAL De Bruijn, M, 70 Right groin pain Ganglion cyst in the MRI: a well- circumscribed Yes Yes N/A Computed tomography Pain completely resolved

201312 radiated to inner thigh obturator foramen cystic mass in the obturator eguided aspiration after the procedure. No A RTICLE without weakness or (extraneural) foramen, indicative of a with steroid injection symptom recurrence at 1 paresthesias ganglion cyst year and 3 months KAO IPNE AL. ET JITPUN EKKAPOT OL NEUROSURGERY WORLD Kim, 201413 M, 63 Right medial thigh pain Acetabular paralabral MRI: a well-defined Yes Yes Decreased compound Conservative therapy Pain was relieved within a with grade 4 weakness cyst causing obturator lobulated cystic lesion in the muscle action potential and follow-up month, but adductor of right hip adductors neuropathy anteroinferior aspect of of right obturator nerve muscles weakness (extraneural) acetabulum, which extended with denervation persisted to the right obturator nerve change of adductor and lateral wall of lesser muscles pelvis with evidence of denervation of adductor muscles Vidoni, 20185 M, 35 Mild to moderate Ganglion cyst arose MRI: a multiloculated Yes Yes N/A Computed tomography Complete resolution of e 2:e5-29 J e259-e269, 126: degree of hip adduction from transverse ganglion cyst arising from guided aspiration symptoms weakness, pain in right acetabular ligament transverse acetabular buttock and groin with entrapment of ligament, extending obturator nerve anteromedially causing marked compression on the obturator nerve with evidence of denervation of

UNE adductor muscles

2019 Munugani, F, 59 Left groin pain below Obturator nerve MRI: a T2 hyperintense No Yes, with N/A Surgical exploration Asymptomatic and no cyst 201814 the inguinal ligament ganglion cyst lesion in the left obturator connection evidence of labral with complete cyst recurrence on MRI at 6 radiating to inner thigh canal with multiple thin tear removal, preserving the months follow-up internal septa compatible obturator nerve with ganglion cyst Bachar Avnieli, M, 52 Right groin and medial Obturator nerve MRI: intrapelvic ganglion Yes Yes, with N/A Hip arthroscopy for Pain free and resumed 201815 thigh pain and reduced ganglion cyst cyst medial to right ilio- evidence of labral decompression of the normal gait pattern in 3 sensation of medial ischial line. The cyst stalk tear ganglion cyst and weeks www.journals.elsevier.com/world-neurosurgery thigh with abnormal communicated directly with dilatation of stalk MRI at 6 months showed gait pattern with right the medial hip joint with opening complete elimination of leg in an external denervation and atrophy of cyst rotated and abducted right obturator externus position muscle BUAO NRNUA AGINCYSTS GANGLION INTRANEURAL OBTURATOR M, male; MRI, magnetic resonance imaging; F, female; N/A, not available. O RIGINAL e265 A RTICLE ORIGINAL ARTICLE EKKAPOT JITPUN ET AL. OBTURATOR INTRANEURAL GANGLION CYSTS

Figure 3. Reinterpretation of other cases in the the pelvis shows intraneural cyst arising from an literature. (AeC) Fluid-sensitive (T2-weighted) inferior labral tear (small arrow) with proximal cyst magnetic resonance images with fat suppression from extension on the obturator nerve (arrows) (modified 3 previously reported cases. (A) Oblique coronal image with permission from Ref.15). (C) Straight coronal showing the multiloculated cyst arising from an inferior image showing the intraneural cyst arising from a labral labral tear and extending proximally along the obturator tear (small arrows) and extending through the obturator nerve (arrows). The normal left obturator nerve is foramen (large arrow) (modified with permission from indicated as ON (arrowheads) (modified with Ref.7). permission from Ref.11). (B) Straight coronal image of

Plain films showed mild degenerative changes in the hip and to our cases. In those cases with MR results, the imaging features sacroiliac joints. EMG showed a chronic right obturator neurop- were also the same. Of these cases, we identified 2 others with clear athy. Ultrasound-guided nerve block significantly improved her evidence of an (unrecognized) connection between the cyst and a pain. MRI of the pelvis and lumbar spine showed a markedly T2 labral tear in this group. One case had radiologic evidence of sub- hyperintense lesion that followed the course of the obturator nerve acute and chronic denervation in the adductor muscles. from the obturator canal up to the pelvic brim with sausage-like Of the 11 nonspecific lesions (Table 3), 9 cases were enlargement (6.5 cm  0.8 cm) of the nerve just below the edge of reinterpreted to be intraneural ganglia, of which 7 were reported the pelvic brim. There was no gadolinium enhancement in the to be joint related by the original investigators. From our lesion and no denervation changes in the adductor muscles. The imaging review, 8 were joint related, 4 were associated with patient was diagnosed with an obturator neurofibroma. A year labral tears, and 4 had radiologic evidence of adductor muscle after the diagnosis, the nerve tumor was removed at another denervation, with similar radiologic features to the other hospital. An anterior retroperitoneal approach to the right lumbar intraneural cyst cases (Figure 3). The remaining 2 cases were plexus showed a dense lipomatous mass firmly adherent to the L3 believed to represent an enlarged iliopsoas bursa, which caused nerve root approximately 3 cm long as it emanated from the L3 external nerve compression,16 and an extraneural ganglion cyst foramen and into the lumbar plexus. Debulking of the mass affecting the obturator nerve.17 encasing the right L3 nerve and L3 neurolysis was performed. Pathologic examination showed dense fibrous connective tissue DISCUSSION and fibroadipose tissue and a minute fragment of nerve with no Although intraneural ganglion cysts are increasingly reported in evidence of a nerve sheath tumor. The patient was pain free at the literature, those arising from the hip joint are rare.3 Among 2-year postoperative follow-up. the reported cases and those from our institution, we found examples that were previously unrecognized as intraneural Literature Review ganglion cysts or misdiagnosed as other entities (e.g., an Fifteen cases of cystic lesions involving the obturator nerves were isolated acetabular paralabral cyst, a cystic neurofibroma found in our search.4-18 These cases included 4 intraneural gan- [case illustration 2 discussed earlier], and a groin hernia).14 glion cysts, of which only 1 was identified as joint connected by We also found another case of an intraneural ganglion cyst in the original authors (Table 2); and 11 nonspecific cysts that the pelvis, but the report did not specificallyidentifywhich affected the obturator nerve (1 compressed the femoral nerve as nerve was affected.21 There are other types of cystic lesions well) (Table 3); the nerveecyst relationship was not clearly around the hip from various pathologic factors that can lead described. to misdiagnoses.19,20 MRI interpretation by an experienced Of the 4 reported cases suggestive of being intraneural cysts, the 3 musculoskeletal or neuroradiologist familiar with intraneural cases with reported MRIs were re-reviewed; each of these 3 cases ganglioncystsisimportant. was confirmed as an intraneural ganglion cyst with a joint origin based on the images included in the reports. As expected, all cysts Pathoanatomy arose from the anteromedial hip joint and propagated into the main The formation of obturator intraneural ganglion cysts is consistent obturator nerve. All reported cases had similar clinical presentations with the proposed unified articular (synovial) theory (Figure 4).2

e266 www.SCIENCEDIRECT.com WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2019.02.029 ORIGINAL ARTICLE EKKAPOT JITPUN ET AL. OBTURATOR INTRANEURAL GANGLION CYSTS

Figure 4. Normal and pathoanatomy of obturator intraneural cysts: all are joint-connected, obturator intraneural and extraneural cysts (with ascend along an articular branch, to the obturator permission, Mayo Foundation, 2018). (Left panel) The nerve, through the obturator canal and into the pelvis normal anatomy of the articular branch of the obturator with the characteristic balloon sign. (Right lower panel) nerve innervates the anteroinferomedial part of hip An anterior hip extraneural ganglion cyst. joint. (Right upper panel) Proposed pathways for

The hip joint, a , is the origin. The hip is a common degenerative changes of both hip joints and 1 case (case 1) had cam- site of degenerative arthritis, and labral tears typically occur as part type femoroacetabular impingement (FAI) morphology character- of the degenerative process. An articular branch supplying the hip ized by features such as a dysplastic bump at the headeneck junc- joint serves as the conduit for the fluid to pass from a tion, a synovial herniation pit, and a pistol-grip deformity of the hip labrocapsular defect into the obturator nerve. Propagation of the joint, which can cause primary chondral injury and lead to degen- fluid occurs within the epineurium; fluid may extend to the erative joint disease.25,26 It is important for an orthopedic surgeon to parent nerve via a path of least resistance, typically in a evaluate the hip joint and obtain radiographs of the hip as well as proximal direction, which depends on pressure and pressure MRI of the cyst.3 Joint disease was not mentioned in most reported fluxes. The appearance of the intraneural cyst often produces a cases. We believe that it is critical to evaluate for joint disease in balloon sign on MRI.22 Most cases have cystic involvement of patients with periarticular cystic lesions. the obturator nerve at the obturator canal and an ascending A joint connection was mentioned in most reported cases; pattern into the intrapelvic region of the obturator nerve. The however, many are not aware of the articular branch anatomy and hip joint is innervated in territories by the femoral nerve, are not knowledgeable about the pathoanatomy of intraneural obturator nerve, superior gluteal nerve, the sacral plexus ganglion cysts and their MRI features, leaving the relationship of through the nerve to the quadratus femoris, the accessory the cyst and involved nerve unclear in the original reports. These obturator nerve (when present), and possibly by branches of the joint connections are not always obvious; they may be small, easy lumbar sympathetic ganglia.23,24 Any of these nerves can be sites to miss depending on the MRI technique, or located seemingly of intraneural ganglion cysts.3 remote from the cysts.2,27 Another common characteristic in both our cases is the presence From an anatomic standpoint, reinterpretation of the limited of some degree of articular disease. The plain films show published preoperative images in 11 of 13 cases in the literature

WORLD NEUROSURGERY 126: e259-e269, JUNE 2019 www.journals.elsevier.com/world-neurosurgery e267 ORIGINAL ARTICLE EKKAPOT JITPUN ET AL. OBTURATOR INTRANEURAL GANGLION CYSTS

(imaging was not provided in 2 reports)6,10 and both our cases Attention more recently has been directed to identify and showed evidence of a joint connection. Labral tears were also disconnect the joint connection from the cyst and/or to treat the identified at the origin of the cyst in some cases.7,8,11,14,15,18-20 In 2 joint disease via a joint-based open or a minimally invasive cases,4,5 the cysts were reported to originate from the transverse (endoscopic or arthroscopic) approach.28-32 Joint and capsular acetabular ligament as a cause of the obturator nerve entrapment. repair without cyst decompression or disconnection of the artic- The transverse acetabular ligament is a part of the hip joint; thus, ular branch also showed promising results in one of our cases from our reinterpretation, the cysts originated from the joint (case 1). The joint and joint capsule repair procedures were solely capsule and an intraneural cyst is a more plausible diagnosis. We performed without exploration of the cyst, nerve trunk, or joint believe that a joint connection is present in all these cases, even connection of the obturator nerve. Several cases treated via when not identified/reported by the investigators. minimally invasive joint-based approaches were believed to involve extraneural disease,15,30 but from our review, they are 15 Treatment Implications intraneural cysts. In a recent study, an obturator intraneural Different treatment options have been described over the years. ganglion cyst was treated by hip arthroscopy for decompression Kim et al.13 reported a patient managed with conservative of the ganglion cyst and dilatation of the stalk opening. The treatment and subsequent follow-up. Pain was relieved within a patient was pain free after the operation, and MRI at 6 months month, but the adductor muscles weakness and atrophy persisted. showed complete elimination of cyst. These approaches correct Computed tomographyeguided aspiration was performed in 2 the primary pathogenesis of the formation of the cyst and also cases5,12 and ultrasound-guided cyst aspiration was also per- decrease the risk of nerve injury from extensive neurolysis or e formed in 2 cases,4,8 all leading to complete resolution of symp- nerve cyst resection. toms. Cysts are dynamic and their dimensions and symptoms may Knowledge of the pathoanatomy that can help guide fluctuate over time; cyst size does not necessarily correlate with recommendations for the hip are based on this review and the presence of or severity of symptoms.27 We do not believe that inference from outcome-based treatment in other more com- nonoperative treatment produces predictable opportunities for mon joint-related cysts at another analogous site (e.g., shoul- 28,29,31 fi maximal pain and neurologic improvement or cyst resolution at derorknee). The uni ed (synovial) articular theory long-term clinicoradiologic follow-up. supports addressing the joint or the articular branch rather fi than the cyst. Intraneural recurrence occurred in 1 reported In some reported cases, attention was rst directed at the cyst. 10 Removal of the cyst and resection of the obturator nerve was re- case after multiple previous resections of a ganglion cyst. We ported in 2 cases9,10; both subsequently developed persistent post- believe that intraneural or extraneural recurrences can occur when joint/capsule disease exists.3,10 Data from a previous operative adductor muscles weakness and sensory abnormality; in 1 1 case, the obturator vessels were also resected.9 In 3 cases,6,7,14 systematic review of joint-related cysts suggested that failure surgical exploration was performed, the cyst was successfully to disconnect the articular branch (cystic joint connection) or fi separated and removed, and the obturator nerve in each case was addressthejointisastatisticallysignicant risk factor for preserved. This approach needs more invasive surgical exploration cyst recurrence. and extensive neurolysis. In our experience, separation of the cyst from the nerve cannot be easily achieved without risk of nerve CONCLUSIONS damage. From personal communication, a combined groin expo- Based on our literature review and clinical experience, we believe sure and retroperitoneal dissection was performed to decompress that the articular theory can explain all cases of intraneural gan- the cyst in a case reported by Heinen et al.18 The investigators did not glion cysts and also all periarticular cysts, including those near the mention a joint connection (but one can be appreciated in an hip. Future experience with treatment targeted to address the unpublished MRI). The surgical result was not discussed. pathogenesis will further expand our knowledge of this rare entity.

ligament: a report of two cases. J Orthop Surg (Hong caused by an acetabular labral cyst: MRI findings. REFERENCES Kong). 2013;21:380-432. AJR Am J Roentgenol. 2005;184:S112-S114. 1. Desy NM, Wang H, Elshiekh MA, et al. Intra- 5. Vidoni A, Sankara STV, Ramana V, Botchu R. neural ganglion cysts: a systematic review and 9. Uchida A, Horiguchi A, Ide H, Hatakeyama N, Ganglion cyst arising from the transverse acetab- reinterpretation of the world’s literature. Yoshimura I, Ogawa Y. Mucoid pseudocyst of the ular ligament (TAL): a rare cause of entrapment of J Neurosurg. 2016;125:615-630. obturator nerve. Int J Urol. 2006;13:471-472. the anterior branch of the obturator nerve. Case report and review of the literature. Skeletal Radiol. 2. Spinner RJ, Atkinson JL, Tiel RL. Peroneal intra- 2019;48:163-165. 10. Kitagawa R, Kim D, Reid N, Kline D. Surgical neural ganglia: the importance of the articular management of obturator nerve lesions. Neurosur- branch. A unifying theory. J Neurosurg. 2003;99: 6. Schwabegger AH, Shafighi M, Gurunluoglu R. An gery. 2009;65:A24-A28. 330-343. unusual case of thigh adductor weakness: obtu- rator nerve ganglion. J Neurol Neurosurg Psychiatry. 11. Sureka J, Panwar S, Mullapudi I. Intraneural gan- 3. Spinner RJ, Hébert-Blouin MN, Trousdale RT, 2004;75:775. glion cysts of obturator nerve causing obturator et al. Intraneural ganglia in the hip and pelvic neuropathy. Acta Neurol Belg. 2012;112:229-230. 7. Campeas S, Rafii M. Pelvic presentation of a hip region. Clinical article. J Neurosurg. 2009;111: joint ganglion: a case report. Bull Hosp Jt Dis. 2002; 317-325. 61:89-92. 12. de Bruijn KM, Franssen G, van Ginhoven TM. A stepwise approach to ‘groin pain’: a common 4. Botchu R, Esler CN, Lloyd DM, Rennie WJ. 8. Yukata K, Arai K, Yoshizumi Y, Tamano K, symptom, an uncommon cause. BMJ Case Rep. Ganglia arising from the transverse acetabular Imada K, Nakaima N. Obturator neuropathy 2013;2013.

e268 www.SCIENCEDIRECT.com WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2019.02.029 ORIGINAL ARTICLE EKKAPOT JITPUN ET AL. OBTURATOR INTRANEURAL GANGLION CYSTS

13. Kim SH, Seok H, Lee SY, Park SW. Acetabular 20. Yukata K, Nakai S, Goto T, et al. Cystic lesion 29. Prasad NK, Spinner RJ, Smith J, et al. The suc- paralabral cyst as a rare cause of obturator neu- around the hip joint. World J Orthop. 2015;6: cessful arthroscopic treatment of suprascapular ropathy: a case report. Ann Rehabil Med. 2014;38: 688-704. intraneural ganglion cysts. Neurosurg Focus. 2015; 427-432. 39:E11. 21. Adamek D, Jagers C, Hejnold M, Jach R, 14. Munugani S, Freeman P, Franz R, Patel B. Obturator Galarowicz B. Intraneural pseudocyst (so-called 30. Hwang DS, Kang C, Lee JB, Cha SM, Yeon KW. nerve ganglion cyst: masquerading as groin hernia ganglion) in an unusual retroperitoneal peri- Arthroscopic treatment of piriformis syndrome by [e-pub ahead of print]. ANZ J Surg.2018.https:// adnexal location? Diagn Pathol. 2014;9:150. perineural cyst on the sciatic nerve: a case report. doi.org/10.1111/ans.14896. Accessed October 10, Knee Surg Sports Traumatol Arthrosc. 2010;18:681-684. 2018. 22. Spinner RJ, Desy NM, Amrami KK, Vosoughi AR, Klaue K. Expanding on the term "balloon" sign. 31. He R, Guo L, Yang L, Chen GX, Duan XJ, Luo CF. 15. Bachar Avnieli I, Amar E, Efrima B, Kollander Y, Acta Neurochir (Wien). 2016;158:1891-1893. [Knee arthroscopic resection of articular capsule Rath E, Volaski H. Hip arthroscopy as a treatment valvular treat popliteal cysts]. Zhonghua Wai Ke Za for obturator neuropathy secondary to intra-pelvic 23. Gardner E. The innervation of the hip joint. Anat Zhi. 2013;51:417-420 [in Chinese]. ganglion: a case report. J Hip Preserv Surg. 2018;5: Rec. 1948;101:353-371. 319-322. 32. Kim JL, Do JG, Yoon YC, Lim SJ, Sung DH. Intraneural ganglion cyst of the sciatic nerve 24. Birnbaum K, Prescher A, Hessler S, Heller KD. 16. Stuplich M, Hottinger AF, Stoupis C, treated using arthroscopic hip surgery: A case The sensory innervation of the hip jointean Sturzenegger M. Combined femoral and obturator report [e-pub ahead of print]. PM R. 2019. https:// anatomical study. Surg Radiol Anat. 1997;19:371-375. neuropathy caused by synovial cyst of the hip. doi.org/10.1002/pmrj.12090. Accessed November Muscle Nerve. 2005;32:552-554. 7, 2018. 25. Fadul DA, Carrino JA. Imaging of femo- 17. Issuu. Pedunculated paralabral cyst emanating roacetabular impingement. J Bone Joint Surg Am. from inferior labrum/transverse acetabular liga- 2009;91(suppl 1):138-143. Conflict of interest statement: The authors declare that the ment. Available at: https://www.hss.edu/Issou_ article content was composed in the absence of any 26. Field RE, Rajakulendran K. The labro-acetabular Case_67.pdf. Accessed November 7, 2018. commercial or financial relationships that could be construed complex. J Bone Joint Surg Am. 2011;93(suppl 2): as a potential conflict of interest. 18. Heinen C, Schmidt T, Kretschmer T. Retroperitoneal 22-27. peripheral nerve tumoursesurgical strategies and inter- Received 10 January 2019; accepted 2 February 2019 disciplinary management. Abstract presented at: 27. Wilson TJ, Hebert-Blouin MN, Murthy NS, Citation: World Neurosurg. (2019) 126:e259-e269. Kongress der Deutschen Gesellschaft für Chir- Garcia JJ, Amrami KK, Spinner RJ. The nearly https://doi.org/10.1016/j.wneu.2019.02.029 urgie 2016 and a personal communication. April invisible intraneural cyst: a new and emerging part 26-29. 2016. Berlin, Germany. of the spectrum. Neurosurg Focus. 2017;42:E10. Journal homepage: www.journals.elsevier.com/world- neurosurgery 19. Panwar J, Mathew A, Thomas BP. Cystic lesions of 28. Prasad N, Wolanskyj AP, Amrami KK, Spinner RJ. Available online: www.sciencedirect.com peripheral nerves: are we missing the diagnosis of Clinical anatomy leading the way for solutions: an ª the intraneural ganglion cyst? World J Radiol. 2017; important paradigm for translational research. 1878-8750/$ - see front matter 2019 Elsevier Inc. All 9:230-244. Clin Anat. 2016;29:978-979. rights reserved.

WORLD NEUROSURGERY 126: e259-e269, JUNE 2019 www.journals.elsevier.com/world-neurosurgery e269