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Intraneural and Extraneural Ganglion Cysts at the Greater Sciatic Notch Involving the Sciatic Nerve Causing Sciatica: Two Case Reports

Intraneural and Extraneural Ganglion Cysts of the Sciatic Nerve

Article information

Nerve. 2024;10(2):113-125
Publication date (electronic) : 2024 October 14
doi : https://doi.org/10.21129/nerve.2024.00563
Byung-chul Son,1,2
1Department of Neurosurgery, Seoul St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
2Catholic Neuroscience Institute, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
Corresponding author: Byung-chul Son Department of Neurosurgery, Seoul St. Mary’s Hospital, Catholic Neuroscience Institute, College of Medicine, The Catholic University of Korea, 222 Banpo-daero, Seocho-gu, Seoul 06591, Republic of Korea Tel: +82-2-2258-6122 Fax: +82-2-594-4248 E-mail: sbc@catholic.ac.kr
Received 2024 March 30; Revised 2024 April 27; Accepted 2024 May 13.

Abstract

Intraneural ganglion cysts (IGCs) are benign mucinous cysts within the epineurium of peripheral nerves. Hip joint-related IGCs are much rarer than those that arise from peripheral nerves around the joints of limbs. The unifying articular synovial theory has been accepted as explaining the pathogenesis of IGCs. Herein, we present two cases of hip joint-related ganglion cysts—one case of an IGC and one case of an extraneural ganglion cyst—that involved the sciatic nerve through the articular branch of the hip joint and caused sciatica. Preoperative and postoperative magnetic resonance imaging (MRI) findings of the articular branch derived from a paralabral cyst of the hip are presented, as well as photographic findings of a ganglion cyst with the articular branch addressed through a transgluteal approach. Despite improvement in postoperative sciatica due to cyst decompression and treatment aimed at addressing the articular branch, the articular branch remained present on postoperative MRI. Unlike IGCs arising from peripheral nerves associated with limb joints, involvement of the sciatic nerve might make it challenging to treat articular branches due to the location of the sciatic nerve over the greater sciatic notch of the deep gluteal region.

Keywords: Ganglion cysts; Hip joint; Sciatic nerve; Sciatica; Intraneural ganglion

INTRODUCTION

Intraneural ganglion cysts (IGCs) are benign mucinous cysts originating within the epineurium of peripheral nerves1,3,14,18,19). They occur most commonly in the peroneal nerve. However, they have also been described in many nerves in the vicinity of synovial joints2,14,18,19). Synovial cysts or ganglions derived from synovial joints are well-known diseases2,14,18,19). They may arise from joint capsules, ligaments, tendon sheaths, bursae, or subchondral bone3,14,18,19). They typically result in neurologic deficits due to displacement of nerve fascicles by cyst contents3,14,18,19). Although the pathogenesis of IGC has long been controversial, a unifying articular theory has been proposed and is now generally accepted3,10,14,18,19). It suggests that IGC forms when mucinous fluid extending from a capsular defect of a neighboring joint propagates along articular branches of the nerve while following the path of least resistance3,10,14,18,19). Once thought to be exceedingly rare, IGCs are being described more frequently due to advances in imaging of nerve-related disorders15).

Among IGCs occurring at various sites, IGC in the hip/pelvic region is rare. However, it is likely to be more frequent than commonly thought2,15). IGCs involving sciatic, obturator, superior gluteal, and femoral nerves, which had connections to the hip joint via articular branches, were first reported by Spinner et al.17). Since the first report, reports of IGCs showing articular connection with the hip have increased, with 54 IGCs reported in 53 patients by 202215). Indeed, the hip joint is innervated by many articular branches of peripheral nerves, including femoral, obturator, superior gluteal, sciatic, and quadratus femoris nerves7). Recent studies on IGCs of the hip have demonstrated the development of IGCs according to the geography of articular branches to specific locations of labrocapsular tears in capsular areas (quadrants)5,10). These findings are consistent with the unified articular (synovial) theory and Hilton’s law4,15). We describe two cases of hip joint-related ganglion cyst, one case of IGC and one case of extraneural ganglion cyst, involving the sciatic nerve through the articular branch of the hip joint cyst and caused sciatica. Reports of IGC involving the sciatic nerve are rare, but reports showing detailed images of extraneural ganglion cysts arising in the hip and involving the sciatic nerve are even rarer. We hope to add our experience to hip-related IGCs reported to date.

CASE REPORT

Case 1

A 67-year-old female patient presented with severe pain and paresthesia in her left buttock and left lower extremity that had persisted for one year. A year before admission, pain accompanied by numbness gradually occurred in the left hip joint and left leg every time the patient walked. It gradually became more severe. Two months before admission to the hospital, the pain became so severe that the patient had to rest for more than two days if she walked for more than 30 min. Eventually, the pain occurred even at rest and lasted all day. She received medication and physical therapy at a neurosurgery clinic. However, there was no improvement. An magnetic resonance imaging (MRI) of the lumbar spine showed no abnormalities, but a cyst was found around the left sciatic nerve in an ultrasound examination of the left hip. She was referred to the author's outpatient clinic for treatment of sciatic neuropathy caused by a juxta-neural cyst. Her pain radiated from her left buttock to the posterior thigh, along distribution of the peroneal nerve to the left big toe. There was no pain in her back. On neurological examination, no obvious sensory disturbance or muscle weakness of the left lower extremity including the foot was found. Deep tendon reflex was normoactive. Straight leg raising test showed a limitation of about 60 degrees. There was no motion limitation or pain in the hip joint, including flexion, adduction, and internal rotation (FADIR). Contrast-enhanced, 3T-MR neurography of the pelvic bone was requested to evaluate a cyst around the sciatic nerve.

An MRI showed a multilobular cyst displacing the nerve fascicle within the sciatic nerve (Fig. 1). It was connected to the paralabral cyst of the left hip joint through multiple slit-like channels thought to be articular branches (Fig. 1). These findings confirmed an IGC of the left sciatic nerve originating from the hip joint. Considering medical intractability, surgical exploration was performed via a transgluteal approach11-13).

Fig. 1.

Preoperative images obtained for a patient (case 1) with a sciatic intraneural ganglion cyst. (A) Axial fat-suppressed T2-weighted image showing a paralabral cyst (arrowhead) in the posterior quadrant, continuing through a slit-like channel (arrow) judged to be the articular branch, running along the posterior acetabulum. The asterisk represents the extension of an intraneural ganglion cyst located within the sciatic nerve (black arrows). The line in the inset shows the level at which the corresponding axial image was taken. (B) Axial fat-suppressed T2-weighted image at the level of the greater sciatic notch, taken 4 mm caudal to the level in Fig. 1A. The image shows that neural contents (black arrows) are displaced due to the ganglion cyst (asterisk) within the sciatic nerve. Note the corresponding articular branch (white arrow) of the paralabral cyst (arrowhead) in the posterior quadrant of the left hip joint. (C-F) Serial coronal T2-weighted images showing propagation of the intraneural ganglion cyst from the paralabral cyst (arrowheads) through the articular branch to the sciatic nerve. Articular branches (white arrows), which appear as multiple slit-like channels, are connected to the proximal sciatic nerve (asterisk in Fig. 1E). This cyst displaced the nerve fascicles (black arrows) through its downward descent (asterisk in Fig. 1F). The line in the inset shows the level at which the corresponding coronal image was taken.

The surgery was performed under a microscope with the patient in a prone position under general anesthesia. Intraoperative neurophysiologic monitoring was performed to confirm the localization of the sciatic nerve and its branches and prevent nerve damage11-13). After opening the lateral edge of the sacrotuberous ligament and resecting the piriformis overlying the sciatic nerve at the greater sciatic notch, the involved portion of the left sciatic nerve was exposed (Fig. 2A). The sciatic nerve showed significant swelling due to an IGC. Through circumferential dissection of the sciatic nerve, severe fibrosis and adhesion in the articular branches and their connections were discovered on the ventral side of the sciatic nerve. The fibrocapsular portion of the articular branch attached to the sciatic nerve was opened first (Fig. 2B). The mucinous content in the intraneural ganglion and the articular branch flowed out. The articular branch was embedded in the fibrocartilaginous ligament above the greater sciatic notch, making further circumferential dissection of tubular structures within it difficult (Fig. 2C). The fibrocapsular tunnel of the articular branch was cut and the connection with the sciatic nerve was dissected and removed using bipolar coagulation (Fig. 2D). Two connections were identified and removed under the surgical field (Fig. 2C). Afterwards, drainage of the mucinous content was performed using gentle finger compression on the swollen sciatic nerve (Fig. 2E). After securing circumferential dissection of the sciatic nerve at the sciatic notch, the overlying wound was closed in layers.

Fig. 2.

Intraoperative findings of a sciatic intraneural ganglion through a transgluteal approach. (A) Intraoperative photograph of the exposed intraneural ganglion containing the sciatic nerve after resection of the lateral edge of the sacrotuberous ligament and the piriformis muscle using a transgluteal approach. In the sciatic nerve (asterisks) exposed at the level of the greater sciatic notch, the distal portion of the sciatic nerve with ganglion cyst involvement (double asterisks) shows more swelling than its proximal part (single asterisk). Arrowheads (white and black) represent areas where the articular branches adhere to the sciatic nerve. (B) Intraoperative photograph showing mucinous content (arrow) of the ganglion cyst flowing out when the articular branch (arrowhead), which is located between fibrous ligaments, is opened in the area indicated by the white arrow on the medial inferior aspect of the sciatic nerve (asterisk). The double asterisks indicate the distal portion of the sciatic nerve that is being retracted to open the articular branch. (C) Intraoperative photograph showing that another articular branch (black arrowheads) found more proximally than the location of the articular branch (white arrowhead) in Fig. 2B is connected to the ventral aspect of the sciatic nerve (asterisk). Severe adhesions with the surrounding tissues and fibrosis are present. (D) Intraoperative photograph showing disconnection and opening of the articular branch (arrowheads) connected to the ventral side of the sciatic nerve (asterisk). After drainage of the mucoid contents, the lumen of the fibrous tunnel of the articular branch (arrowheads) is identified. (E) Intraoperative photograph showing the appearance of the sciatic nerve after disconnection of the two articular branches (black and white arrowheads) and the drainage of the mucous contents of the ganglion cyst by gentle squeezing of the nerve. Significant decompression of the swollen sciatic nerve is evident (double asterisks). GM: gluteus maximus muscle retracted; IGN: branches of the inferior gluteal nerve; PMc: cut edge of the resected piriformis muscle; OI/Gm: obturator internus and gemellus muscle.

The patient's left buttock and sciatic pain in her left leg significantly improved the day after surgery, making ambulation possible. The patient was discharged on the 4th day after surgery. The pain and spontaneous pain in the left hip and lower extremity when walking did not occur thereafter. Medical treatment for pain and mild numbness at the hip incision was used until two months after surgery. It was discontinued at 3 months after surgery. At 13 months after her surgery, she reported no pain or discomfort in her buttocks or left lower extremity. In an MRI performed 13 months after surgery, the articular branch remained intact despite the complete disappearance of the IGC of the sciatic nerve (Fig. 3).

Fig. 3.

Postoperative images of a patient (case 1) obtained 13 months after surgery. (A) Axial fat-suppressed T2-weighted image at the same level as in Fig. 1A before surgery. The paralabral cyst (arrowhead) and articular branch (arrow) are still present. However, the intraneural ganglion cyst of the sciatic nerve (asterisk) has disappeared. There was no recurrence of the cyst on magnetic resonance imaging. The line in the inset shows the level at which the corresponding axial image was taken. (B) Coronal T2-weighted maximum intensity projection images at the same level as in Fig. 1D. The existence of the articular branches is still observable. The line in the inset shows the level at which the corresponding coronal image was taken. (C) Coronal T2-weighted maximum intensity projection images at the same level as in Fig. 1F. Despite the presence of residual articular branches, the ganglion within the sciatic nerve (black arrows) has disappeared. The line in the inset shows the level at which the corresponding coronal image was taken.

Case 2

A 69-year-old male patient presented with pain in his right hip and left lower extremity that had persisted for two years. The pain suddenly started in his right buttock and posterior thigh and gradually worsened, spreading to his posterolateral leg and foot. The pain in the right hip joint persisted in a stabbing form. It radiated to the lower extremities when walking or standing. These symptoms became less severe when he lay down and rested. However, they became especially worse when he sat down. His hip pain gradually worsened over several months until he was unable to sit down. Medication, physical therapy, and interventional blocks had no significant effect on his pain. He was diagnosed with lumbar stenosis at a tertiary hospital. He underwent a posterior interbody fusion between the L4/5 vertebrae. However, there was no improvement at all. An additional L5/S1 decompression with interbody fusion surgery was performed five months later. There was no improvement in pain. Because his sciatic pain did not improve despite drug treatment, including opioids, he visited the author's outpatient clinic.

Physical examination showed mild limitation of lumbar flexion and extension without lower back pain. FADIR testing of his right hip joint revealed pain in his buttocks with limitation. The straight leg raise test of his right lower extremity was limited to 45 degrees. Neurological examination revealed no abnormalities such as foot weakness or obvious sensory impairment. The pain was severe when sitting. Thus, he sat in the typical labor pain position with her right hip raised. He could not sit for more than five min. Therefore, the interview was conducted standing. His pain was extending from the right retro-trochanteric buttock down the peroneal division of the left lower extremity. He expressed that his buttocks hurt as if being stabbed by an awl and that his legs felt less painful when he walked. An MRI of the hip joint was requested because he had typical symptoms of piriformis syndrome (sciatic nerve entrapment in the greater sciatic notch) presenting with sciatica and sitting intolerance.

MRI revealed a multi-lobular cyst attached to the medial side of the right sciatic nerve at the level of the sciatic notch with displacement of the sciatic nerve bundle (Fig. 4). The right sciatic nerve showed type B variation along with the piriformis muscle. Although the cyst was attached to the tibial division of the sciatic nerve and severely displaced the nerve bundle, it did not spread to the inside of the nerve (Fig. 4). Therefore, it was determined to be an extraneural ganglion cyst adherent to the sciatic nerve, fed through an articular branch derived from the paralabial cyst of the hip joint. Since adhesion of the extraneural ganglion cyst to the sciatic nerve might have contributed to piriformis syndrome, cyst exploration with sciatic nerve decompression was planned. A transgluteal approach was performed with intraoperative neurophysiological monitoring to prevent nerve injury17-19).

Fig. 4.

Preoperative images of a patient (case 2) with a sciatic intraneural ganglion cyst and failed back surgery syndrome. (A) A fat-suppressed, axial T2-wieghted image above the greater sciatic notch shows a multilobular cyst (asterisk) adhering to the sciatic nerve and displacing the nerve fascicle (black arrows). The asterisk represents an intraneural ganglion cyst in the sciatic nerve. The line in the inset shows the level at which the corresponding coronal image was taken. (B) Axial fat-suppressed T2-weighted image, taken 12 mm caudal to the level in Fig. 4A. A slit-like tubular structure (arrow) connected to the sciatic intraneural ganglion runs along the posterior wall of the acetabulum of the right hip joint. (C) Axial fat-suppressed T2-weighted image, taken 16 mm caudal to the level in Fig. 4A. A slit-like structure (arrow), thought to be the articular branch is connected to the paralabral cyst (arrowhead) in the posterior quadrant of the right hip joint. (D) A sagittal T2-weighted image showing the ganglion cyst of the sciatic nerve connected to a slit-like tubular structure at its base. The line in the inset shows the level at which the corresponding coronal image was taken. (E) A sagittal T2-weighted image taken 20 mm lateral to the level in Fig. 4D, showing the articular branch of the ganglion cyst running along the posterior acetabulum. (F) A sagittal T2-weighted image taken 14 mm lateral at the level of Fig. 4E, showing the articular branch of the ganglion cyst (arrow) originating from the paralabral cyst (arrowhead) of the right hip joint. (G) A fat-suppressed, coronal T2-weighted image showing a multilobular ganglion cyst (asterisk) involving the tibial division (white arrow) of the sciatic nerve (arrowhead). The sciatic nerve and the piriformis muscle show type B variation (white and black arrows). The line in the inset shows the level at which the corresponding coronal image was taken. (H) Coronal T2-weighted image taken 12 mm ventral to the level of Fig. 4G, showing the articular branch of the ganglion cyst extending along the posterior acetabulum toward the paralabral cyst.

After resection of the major piriformis muscle and tendon at the greater sciatic notch, the peroneal division of the sciatic nerve was exposed (Fig. 5A). After dissection of the accessory piriformis muscle and piriformis tendon, the peroneal and tibial divisions of the sciatic nerve over the greater sciatic notch were exposed. The cyst and articular branch were then addressed (Fig. 5B). The ganglion cyst was severely adherent to the ventromedial aspect of the tibial division of the sciatic nerve. During separation between the nerve and the cyst, the cyst wall ruptured and mucinous contents flowed out. The capsule of the cyst was separated from the fibrocartilage of the greater sciatic notch and cut (Fig. 5C). After securing mobility of the sciatic nerve, the overlying wound was closed in layers. After surgery, the patient's sciatic pain improved immediately. The pain in his right buttock was about half improved. An MRI performed three days after the surgery confirmed that the cyst had completely disappeared, although the articular branch remained as before (Fig. 5D, E).

Fig. 5.

Intraoperative photographs and magnetic resonance images taken on the third day after surgery for case 2. (A) Intraoperative photograph showing circumferential dissection of the peroneal and tibial divisions of the sciatic nerve, with resection of the major and accessory piriformis muscles and tendons at the sciatic notch via a gluteal approach. (B) Intraoperative photograph showing a ganglion cyst (white arrows) exposed by dissection of the ventral portion of the tibial division of the sciatic nerve. (C) Intraoperative photograph showing that the ganglion cyst has been opened and the mucinous content has been removed from the underlying fibrous tubular structure. (D) Fat-suppressed, coronal T2-weighted image shows disappearance of the ganglion cyst with decompression of peroneal (black arrow) and tibial (white arrow) divisions of the sciatic nerve. The line in the inset shows the level at which the corresponding coronal image was taken. (E) A fat-suppressed, axial T2-weighted image showing a small residual cyst (arrowhead) and peroneal (black arrow) and tibial (white arrow) divisions of the sciatic nerve. The line in the inset shows the level at which the corresponding axial image was taken. PdSN: peroneal division of the sciatic nerve; TdSN: tibial division of the sciatic nerve.

Six months after the surgery, he reported that his hip and lower extremity pain, which had improved, worsened again as before surgery. A repeat MRI of the pelvic bone showed a recurrence of a ganglion cyst that had disappeared shortly after surgery (Fig. 6A, B). In addition, the cyst was reconnected with the paralabral cyst of the hip joint through the pre-existing articular branch (Fig. 6). The sciatic nerve bundle was displaced and compressed by this. Reoperation for cyst recurrence with sciatic nerve adhesions was performed using the same approach. On re-exploration, it was confirmed that the cyst had recurred in the same shape as in the first surgery on the medial ventral side of the tibial division of the sciatic nerve (Fig. 7A). After the cyst was separated from the nerve, the mucinous content was aspirated. To prevent further recurrence of the cyst, the fibrous capsule of the articular branch was separated and removed as deeply as possible along the greater sciatic notch (Fig. 7B, C).

Fig. 6.

Magnetic resonance images of recurrence in case 2 at 6 months after surgery. (A) Fat-suppressed axial T2-weighted image showing recurrence of a ganglion cyst (asterisk) displacing fascicles of the sciatic nerve (black arrow). It appears almost identical to the first magnetic resonance image (Fig. 4). A connection with the articular branch (white arrow) is found in the ventral portion of the cyst. (B) Axial fat-suppressed T2-weighted image, taken 16 mm caudal to the level in Fig. 4A. A slit-like articular branch (white arrow) is again connected to the paralabral cyst (arrowhead) of the right hip joint. Black arrow indicates the sciatic nerve. (C) Fat-suppressed, coronal T2-weighted image showing recurrence of a multilobular ganglion cyst (asterisk) involving the tibial division (arrow) of the sciatic nerve. With piriformis muscle resection in the first surgery, type B variation is no longer observed. The line in the inset shows the level at which the corresponding coronal image was taken. (D) Coronal maximal intensity projection image taken 12 mm ventral to the level of Fig. 4C, showing the articular branch (arrow) of the ganglion cyst extending along the posterior acetabulum toward the paralabral cyst (arrowhead). The line in the inset shows the level at which the corresponding coronal image was taken. (E) A sagittal T2-weighted image showing recurrence of the ganglion cyst (asterisk) of the sciatic nerve (arrows). The line in the inset shows the level at which the corresponding sagittal image was taken. (F) Sagittal T2-weighted image taken 14 mm lateral at the level of Fig. 4E, showing the articular branch of the ganglion cyst (arrow) originating from the paralabral cyst (arrowhead) of the right hip joint.

Fig. 7.

Intraoperative images during reoperation for sciatic nerve adhesion due to recurrence of the ganglion cyst. (A) Intraoperative photograph showing the ganglion cyst (arrows) firmly adherent to the ventral side of the tibial division of the sciatic nerve tibial division of the sciatic nerve (TdSN). It looked the same as it did at the time of the first operation Fig. 4A. (B) Intraoperative photograph showing dissection and removal of the proximal portion (white arrows) of the articular branch (black arrows) rising between the gemellus muscle and the acetabulum to prevent recurrence of the ganglion cyst. (C) Intraoperative photograph showing completed dissection and removal of the proximal portion of the articular branch (black arrow) with circumferential decompression of the sciatic nerve. The path by which the articular branch travels from the ventral aspect of the gemellus muscle to the sciatic nerve was dissected. (D) T2-weighted coronal image taken 5 days after surgery, again showing the disappearance of the cyst with decompression of the sciatic nerve (black arrow). However, the proximal pathway (white arrow) of the articular branch remained present. The white arrowhead shows where the articular branch was removed. The line in the inset shows the level at which the corresponding coronal image was taken. (E) Sagittal T2-weighted image showing persistence of the proximal portion (white arrow) of the ganglion cyst. The degree of dissection of articular branches (white arrowhead) is noted ventral to the gemellus muscle (black arrowhead). The black arrow indicates the decompressed sciatic nerve. PdSN: peroneal division of the sciatic nerve; SN: the sciatic nerve.

An MRI performed 5 days after the surgery confirmed that the ganglion cyst had disappeared again (Fig. 7D). However, it was confirmed that the proximal part of the articular branch still remained (Fig. 7E). No neurological abnormalities occurred after surgery. Six months after surgery, the patient's sciatica was no longer present. There was no stabbing pain in his right hip. He was able to sit for an hr or so. One year after surgery, he assessed that his pain and suffering had decreased by about one-third compared to before. He still needed medication for the dull pain in his buttocks. The patient refused additional MRI to check the status of the cyst and articular branch.

DISCUSSION

IGC and unifying articular theory

A unifying articular theory for IGCs was proposed in 200314). Based on a large multicenter experience and a review of the literature, Spinner et al.14) proposed the unified articular theory, a logical and anatomical explanation for the formation and propagation of IGCs, as well as insights into their treatment. Citing IGCs in the common peroneal nerve of the fibular neck as a prototype, frequently associated findings of IGC (e.g., fluctuating symptoms, predominant involvement of the deep peroneal nerve, periarticular location, high recurrence rate of 10-20%) and connection to the superior tibiofibular joint (STFJ) have been described14). Joint fluid can escape through the capsular defect of the neighboring joint and extend along articular branches14,15). The fluid then extends to the main parent nerve, following the path of least resistance in a manner dependent on pressure and pressure fluxes3,9). These cysts appear tubular, assuming the anatomy of associated nerves14,15). This articular (synovial) theory for IGCs could also explain the pathophysiology of extraneural ganglion cyst14,15). Extraneural ganglion cysts can also arise from synovial surfaces. They are connected to joints via non-neural pedicles, appearing globular in shape and occasionally resulting in extrinsic nerve compression14,15).

Insights into IGC formation have changed the purpose and direction of surgical treatment for them15). The goal of surgery is to address articular branches and/or the joint of origin to prevent nerve damage and reduce intraneural recurrence. It is recommended to perform a articular branch disconnection/ligation and/or a joint procedure (addressing the capsule or synovial lining) with cyst decompression to eliminate the cyst2,8). For perineural or juxtaneural cysts identified as IGCs on MRI, resection and intraneural dissection of the cysts are no longer recommended8). Cyst decompression performed without addressing the articular branch or articular pathology has been shown to predictably lead to intraneural recurrence, regardless of whether open surgery or percutaneous aspiration is performed2,8). This approach, based on the pathophysiology of IGCs, can improve outcomes and reduce intraneural recurrence2,8,15).

IGC in the sciatic nerve

First cases of IGCs demonstrated to have a connection to the hip joint were reported by Spinner et al.17) in 2009. The report found that all five cases of IGCs involving the sciatic nerve and lumbar plexus had articular connections with the posteromedial aspect of the hip joint. Articular connection with the hip joint was also confirmed in 8 cases of IGCs of the sciatic nerve reported by Shin et al.10) in 2022. This finding was also confirmed in the two cases described in this report, showing that a stereotyped pattern in MRI examination was repeatedly confirmed in sciatic IGCs. Our findings together with previously reported MRI findings of IGCs involving the sciatic nerve6,10,17) fully support the unifying articular theory of IGCs proposed by Spinner et al.8,14-16).

In IGCs involving the sciatic nerve, based on the territorial origin of the posterior labral tear of the hip joint, the nerve to the quadratus femoris and superior gluteal nerves were considered to be corresponding articular branches from which cyst can spread to the sciatic nerve8,16,17). These findings were again confirmed by Shin et al.10). Lesions arising from a paralabral cyst related to a labral tear in the posterior inferior quadrant of the hip joint continued though a narrow channel (articular branch), running along the posterior acetabular wall10). However, controversy has arisen regarding the consistent involvement of the nerve to quadratus femoris in the propagation of sciatic IGCs due to a possibility of ischiofemoral impingement10). Considering the high frequency of hip labral tears and the very rare occurrence of hip-related IGCs, further research is needed to determine why sciatic nerve IGCs originating from the hip occur only in certain patients. Nevertheless, looking at MRI findings of sciatic nerve IGC reported to date, the unifying articular (synovial) theory,15,17) in which cystic mucinous fluid spreads from a tear in the labrum in the posterior inferior quadrant of the hip joint to the proximal sciatic nerve via the articular branch, is the most reasonable and scientific explanation.

Extraneural ganglion cyst in the sciatic nerve

MRI findings for case 2 were similar to those of an IGC directly involving the sciatic nerve (Case 1), except that there was no obvious intraneural extension. Extraneural ganglion cysts are known to occur much more frequently in extremities than IGCs17). However, it is very rare for an extraneural ganglion cyst to involve the sciatic nerve, away from the joint, through its articular branches rather than extending directly from the paralabral cyst of the hip joint. The finding of articular connections in case 2 suggests that this extraneural ganglion cyst shares the same pathophysiology as the intraneural ganglion, namely the articular (synovial) theory17).

We judged that the ganglion cyst in case 2 was a hip joint-related extraneural ganglion involving the sciatic nerve. However, the author's opinion could be refuted as being a simple extension of a paralabral cyst. In fact, the imaging findings in case 2 may be interpreted as similar to those of a paralabral cyst that caused sciatica reported by Sherman et al.9) in 2003. However, extraneural cysts caused by nonneural pedicles that are not constrained by the epineurium are known to be more globular in shape rather than tubular, as pointed out by Spinner et al.17). In addition, extraneural ganglion was not found to be a direct expansion of a paralabral cyst. The extraneural ganglion in case 2 was obviously fed by a slit-like channel connected to the labral tear/rent of the hip joint. Surgical findings of cases 2 were identical to those of case 1, showing obvious ING of the sciatic nerve. Thus, it was judged to be an extraneural ganglion cyst of the sciatic nerve that could be explained by the articular synovial theory.

Treatment of sciatic IGC

Insights from an articular theory into the pathogenesis of IGC have led to changes in the treatment paradigm for these rare lesions. It is recommended to apply the same principles for treating IGCs of the peroneal nerve connected to the STFJ to sciatic nerve IGCs. Treating a hip lesion and addressing the articular branch connection have been recommended as ideal12,17). For rapid nerve decompression of severe sciatica and neurological deficits, limited decompression of the cyst via the same hip approach for addressing the articular branch is recommended15-17). However, complete resection of the cyst and its wall is unnecessary15,17). Isolated cyst decompression or resection of the cyst/nerve resection is no longer recommended8,15-17). Joint procedures including offset procedures, total hip arthroplasty, and labrocapsular repair are being introduced8,15,16). Minimally invasive and arthroscopic approaches are being pioneered to address labral pathology and cyst15). However, reports on treatment of IGC involving the sciatic nerve are limited and optimal management of these lesions is not established yet10). In particular, there is a controversy regarding techniques for cyst decompression of symptomatic IGCs that have invaded the sciatic nerve.

When treating IGCs involving the sciatic nerve, the deep location of the hip joint and the largest peripheral nerve, the sciatic nerve, should be considered. Decompression of the cyst itself might seem straightforward. However, it may not be an easy task for sciatic IGCs located near the sciatic notch in the deep gluteal space. Ultrasound-guided simple aspiration, arthroscopic synovectomy with labial cyst decompression, and transgluteal approach have been reported for cyst decompression of sciatic IGCs10,15,17). However, if cyst decompression accompanied by articular branch disconnection is the goal of treatment, it might be difficult to achieve it with image-guided aspiration. Instead, if addressing the articular branch with cyst decompression is pursued, transgluteal or arthroscopic approaches that can be confirmed under direct vision might be appropriate.

Addressing the articular branch can be accomplished easily through open surgery in superficial joints and nerves such as the STFJ and peroneal nerve, but can be difficult for deeply-located sciatic nerve and hip joint. Therefore, if it is clear that decompressing the cyst alone will improve pain and neurological signs and prevent recurrence, less invasive procedures may be recommended. Arthroscopic decompression was suggested by some authors6,10). However, the author has a different opinion.

Unlike IGCs in the peripheral nerves of extremities, accessing articular branches of the sciatic nerve and hip joint located in the deep gluteal space, is not easy. As can be seen in surgical photos of current cases, it was difficult to find the articular branch directly connected to the cyst in the sciatic notch area due to strong adhesion with the ventral side of the sciatic nerve. Its dissection and cutting were also difficult due to the fibrous sheath. In the first report of sciatic nerve IGCs17), there were also cases in which articular branches could not be addressed during surgery using a transgluteal approach.

The difficulty in addressing the articular branch in sciatic nerve IGCs has been confirmed not only in the transgluteal approach, but also in arthroscopic treatment. To the best of our knowledge, intraoperative photographs demonstrating direct arthroscopic addressing of articular branches have not been reported6,10). In reports suggesting arthroscopic treatment for sciatic nerve IGCs6,10), there has been no surgical photographic evidence demonstrating direct arthroscopic addressing of articular branches. Although our surgical experience was limited, considering severe adhesions on deep, ventral side of the sciatic nerve, it was assumed that only cyst decompression was performed in arthroscopic treatment.

The articular branch of the ganglion cyst of the sciatic nerve, located in the greater sciatic notch is likely to remain even if the articular branch is treated during surgery. In case 1, MRI performed 13 months after treatment showed the presence of articular branches despite complete disappearance of the intraneural ganglion with complete relief of sciatic pain. The persistence of articular branches was confirmed on postoperative follow-up MRI despite improvement in clinical symptoms. It was also described in the first report on sciatic IGCs (case 1, transgluteal approach15,17) and two recent reports recommending arthroscopic treatment6,10).

The extraneural ganglion cyst in case 2 associated with the articular branch recurred within several months despite treatment of the articular branch with cyst decompression. Postoperative MRI showed that the articular branch remained intact despite deeper dissection of the articular branch with repeated exploration. Based on surgical findings (Fig. 2, 5, 7), the authors suspect that chronic fibrosis of the wall can occur when the articular branch of the sciatic nerve passes through the fibrous ligamentous structure around the sciatic notch and changes into an elastic structure.

Therefore, the persistent presence of an isolated articular branch observed on follow-up MRI may not affect the long-term outcome of a sciatic IGC treatment as long as decompression of the involved sciatic nerve through aspiration, arthroscopy, or surgery is sufficient. However, due to the unique location of ganglion cysts involving the sciatic nerve in the deep gluteal space, more experience is needed regarding the extent of cyst decompression and dissection of articular branches.

CONCLUSION

Hip joint-related intraneural and extraneural ganglion cysts, like those of extremities, can be explained by the joint (synovial) theory. Their articular connection can be revealed by careful evaluation of MRI images. The same principles as the treatment for IGCs of the extremities, namely cyst decompression and addressing the articular branches, can be applied to their treatment. However, addressing the articular branch is difficult because the sciatic nerve is located above the greater sciatic notch in the deep gluteal space.

Notes

No potential conflict of interest relevant to this article was reported.

References

1. Allieu PY, Cenac PE. Peripheral nerve mucoid degeneration of the upper extremity. J Hand Surg Am 14:189–194. 1989;
2. Desy NM, Wang H, Elshiekh MA, Tanaka S, Choi TW, Howe BM, et al. Intraneural ganglion cysts: A systematic review and reinterpretation of the world's literature. J Neurosurg 125:615–630. 2016;
3. Giele H, Le Viet D. Intraneural mucoid cysts of the upper limb. J Hand Surg Br 22:805–809. 1997;
4. Hébert-Blouin MN, Tubbs RS, Carmichael SW, Spinner RJ. Hilton's law revisited. Clin Anat 27:548–555. 2014;
5. Janzen DL, Peterfy CG, Forbes JR, Tirman PF, Genant HK. Cystic lesions around the knee joint: MR imaging findings. AJR Am J Roentgenol 163:155–161. 1994;
6. Kim SW, Yoon YC, Sung DH. Intraneural ganglion cysts originating from the hip joint: A single-center experience. Muscle Nerve 66:339–344. 2022;
7. Laumonerie P, Dalmas Y, Tibbo ME, Robert S, Durant T, Caste T, et al. Sensory innervation of the hip joint and referred pain: A systematic review of the literature. Pain Med 22:1149–1157. 2021;
8. Prasad N, Wolanskyj AP, Amrami KK, Spinner RJ. Clinical anatomy leading the way for solutions: An important paradigm for translational research. Clin Anat 29:978–979. 2016;
9. Sherman PM, Matchette MW, Sanders TG, Parsons TW. Acetabular paralabral cyst: An uncommon cause of sciatica. Skeletal Radiol 32:90–94. 2003;
10. Shin N, Kim HS, Lee JH, Cha SY, Cha MJ. Juxtaneural ganglia arising from the hip joint: focus on magnetic resonance imaging findings and clinical manifestations. Skeletal Radiol 51:1439–1452. 2022;
11. Son BC. Importance of sacrotuberous ligament in transgluteal approach for sciatic nerve entrapment in the greater sciatic notch (Piriformis syndrome). J Korean Neurosurg Soc 67:217–226. 2024;
12. Son BC, Lee C. Piriformis syndrome (sciatic nerve entrapment) associated with type C sciatic nerve variation: A report of two cases and literature review. Korean J Neurotrauma 18:434–443. 2022;
13. Son BC, Lee C. The transgluteal approach for decompression of sciatic nerve entrapment (Piriformis syndrome) with intraoperative neurophysiology: A technical note. Nerve 8:59–69. 2022;
14. Spinner RJ, Atkinson JL, Tiel RL. Peroneal intraneural ganglia: the importance of the articular branch. A unifying theory. J Neurosurg 99:330–343. 2003;
15. Spinner RJ, Desy NM, Amrami KK. Intraneural ganglion cysts at the hip: The next celestial frontier. Muscle Nerve 66:236–239. 2022;
16. Spinner RJ, Hébert-Blouin MN, Tanaka S, Amrami KK, Swartz KR, Fee DB, et al. Hip- and pelvic-related intraneural ganglia. J Neurosurg 112:1353–1356. 2010;
17. Spinner RJ, Hébert-Blouin MN, Trousdale RT, Midha R, Russell SM, Yamauchi T, et al. Intraneural ganglia in the hip and pelvic region. Clinical article. J Neurosurg 111:317–325. 2009;
18. Spinner RJ, Scheithauer BW, Amrami KK. The unifying articular (synovial) origin of intraneural ganglia: Evolution-revelation-revolution. Neurosurgery 65:A115–A124. 2009;
19. Spinner RJ, Vincent JF, Wolanskyj AP, Scheithauer BW. Intraneural ganglion cyst: a 200-year-old mystery solved. Clin Anat 21:611–618. 2008;

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Fig. 1.

Fig. 1.

Preoperative images obtained for a patient (case 1) with a sciatic intraneural ganglion cyst. (A) Axial fat-suppressed T2-weighted image showing a paralabral cyst (arrowhead) in the posterior quadrant, continuing through a slit-like channel (arrow) judged to be the articular branch, running along the posterior acetabulum. The asterisk represents the extension of an intraneural ganglion cyst located within the sciatic nerve (black arrows). The line in the inset shows the level at which the corresponding axial image was taken. (B) Axial fat-suppressed T2-weighted image at the level of the greater sciatic notch, taken 4 mm caudal to the level in Fig. 1A. The image shows that neural contents (black arrows) are displaced due to the ganglion cyst (asterisk) within the sciatic nerve. Note the corresponding articular branch (white arrow) of the paralabral cyst (arrowhead) in the posterior quadrant of the left hip joint. (C-F) Serial coronal T2-weighted images showing propagation of the intraneural ganglion cyst from the paralabral cyst (arrowheads) through the articular branch to the sciatic nerve. Articular branches (white arrows), which appear as multiple slit-like channels, are connected to the proximal sciatic nerve (asterisk in Fig. 1E). This cyst displaced the nerve fascicles (black arrows) through its downward descent (asterisk in Fig. 1F). The line in the inset shows the level at which the corresponding coronal image was taken.

Fig. 2.

Fig. 2.

Intraoperative findings of a sciatic intraneural ganglion through a transgluteal approach. (A) Intraoperative photograph of the exposed intraneural ganglion containing the sciatic nerve after resection of the lateral edge of the sacrotuberous ligament and the piriformis muscle using a transgluteal approach. In the sciatic nerve (asterisks) exposed at the level of the greater sciatic notch, the distal portion of the sciatic nerve with ganglion cyst involvement (double asterisks) shows more swelling than its proximal part (single asterisk). Arrowheads (white and black) represent areas where the articular branches adhere to the sciatic nerve. (B) Intraoperative photograph showing mucinous content (arrow) of the ganglion cyst flowing out when the articular branch (arrowhead), which is located between fibrous ligaments, is opened in the area indicated by the white arrow on the medial inferior aspect of the sciatic nerve (asterisk). The double asterisks indicate the distal portion of the sciatic nerve that is being retracted to open the articular branch. (C) Intraoperative photograph showing that another articular branch (black arrowheads) found more proximally than the location of the articular branch (white arrowhead) in Fig. 2B is connected to the ventral aspect of the sciatic nerve (asterisk). Severe adhesions with the surrounding tissues and fibrosis are present. (D) Intraoperative photograph showing disconnection and opening of the articular branch (arrowheads) connected to the ventral side of the sciatic nerve (asterisk). After drainage of the mucoid contents, the lumen of the fibrous tunnel of the articular branch (arrowheads) is identified. (E) Intraoperative photograph showing the appearance of the sciatic nerve after disconnection of the two articular branches (black and white arrowheads) and the drainage of the mucous contents of the ganglion cyst by gentle squeezing of the nerve. Significant decompression of the swollen sciatic nerve is evident (double asterisks). GM: gluteus maximus muscle retracted; IGN: branches of the inferior gluteal nerve; PMc: cut edge of the resected piriformis muscle; OI/Gm: obturator internus and gemellus muscle.

Fig. 3.

Fig. 3.

Postoperative images of a patient (case 1) obtained 13 months after surgery. (A) Axial fat-suppressed T2-weighted image at the same level as in Fig. 1A before surgery. The paralabral cyst (arrowhead) and articular branch (arrow) are still present. However, the intraneural ganglion cyst of the sciatic nerve (asterisk) has disappeared. There was no recurrence of the cyst on magnetic resonance imaging. The line in the inset shows the level at which the corresponding axial image was taken. (B) Coronal T2-weighted maximum intensity projection images at the same level as in Fig. 1D. The existence of the articular branches is still observable. The line in the inset shows the level at which the corresponding coronal image was taken. (C) Coronal T2-weighted maximum intensity projection images at the same level as in Fig. 1F. Despite the presence of residual articular branches, the ganglion within the sciatic nerve (black arrows) has disappeared. The line in the inset shows the level at which the corresponding coronal image was taken.

Fig. 4.

Fig. 4.

Preoperative images of a patient (case 2) with a sciatic intraneural ganglion cyst and failed back surgery syndrome. (A) A fat-suppressed, axial T2-wieghted image above the greater sciatic notch shows a multilobular cyst (asterisk) adhering to the sciatic nerve and displacing the nerve fascicle (black arrows). The asterisk represents an intraneural ganglion cyst in the sciatic nerve. The line in the inset shows the level at which the corresponding coronal image was taken. (B) Axial fat-suppressed T2-weighted image, taken 12 mm caudal to the level in Fig. 4A. A slit-like tubular structure (arrow) connected to the sciatic intraneural ganglion runs along the posterior wall of the acetabulum of the right hip joint. (C) Axial fat-suppressed T2-weighted image, taken 16 mm caudal to the level in Fig. 4A. A slit-like structure (arrow), thought to be the articular branch is connected to the paralabral cyst (arrowhead) in the posterior quadrant of the right hip joint. (D) A sagittal T2-weighted image showing the ganglion cyst of the sciatic nerve connected to a slit-like tubular structure at its base. The line in the inset shows the level at which the corresponding coronal image was taken. (E) A sagittal T2-weighted image taken 20 mm lateral to the level in Fig. 4D, showing the articular branch of the ganglion cyst running along the posterior acetabulum. (F) A sagittal T2-weighted image taken 14 mm lateral at the level of Fig. 4E, showing the articular branch of the ganglion cyst (arrow) originating from the paralabral cyst (arrowhead) of the right hip joint. (G) A fat-suppressed, coronal T2-weighted image showing a multilobular ganglion cyst (asterisk) involving the tibial division (white arrow) of the sciatic nerve (arrowhead). The sciatic nerve and the piriformis muscle show type B variation (white and black arrows). The line in the inset shows the level at which the corresponding coronal image was taken. (H) Coronal T2-weighted image taken 12 mm ventral to the level of Fig. 4G, showing the articular branch of the ganglion cyst extending along the posterior acetabulum toward the paralabral cyst.

Fig. 5.

Fig. 5.

Intraoperative photographs and magnetic resonance images taken on the third day after surgery for case 2. (A) Intraoperative photograph showing circumferential dissection of the peroneal and tibial divisions of the sciatic nerve, with resection of the major and accessory piriformis muscles and tendons at the sciatic notch via a gluteal approach. (B) Intraoperative photograph showing a ganglion cyst (white arrows) exposed by dissection of the ventral portion of the tibial division of the sciatic nerve. (C) Intraoperative photograph showing that the ganglion cyst has been opened and the mucinous content has been removed from the underlying fibrous tubular structure. (D) Fat-suppressed, coronal T2-weighted image shows disappearance of the ganglion cyst with decompression of peroneal (black arrow) and tibial (white arrow) divisions of the sciatic nerve. The line in the inset shows the level at which the corresponding coronal image was taken. (E) A fat-suppressed, axial T2-weighted image showing a small residual cyst (arrowhead) and peroneal (black arrow) and tibial (white arrow) divisions of the sciatic nerve. The line in the inset shows the level at which the corresponding axial image was taken. PdSN: peroneal division of the sciatic nerve; TdSN: tibial division of the sciatic nerve.

Fig. 6.

Fig. 6.

Magnetic resonance images of recurrence in case 2 at 6 months after surgery. (A) Fat-suppressed axial T2-weighted image showing recurrence of a ganglion cyst (asterisk) displacing fascicles of the sciatic nerve (black arrow). It appears almost identical to the first magnetic resonance image (Fig. 4). A connection with the articular branch (white arrow) is found in the ventral portion of the cyst. (B) Axial fat-suppressed T2-weighted image, taken 16 mm caudal to the level in Fig. 4A. A slit-like articular branch (white arrow) is again connected to the paralabral cyst (arrowhead) of the right hip joint. Black arrow indicates the sciatic nerve. (C) Fat-suppressed, coronal T2-weighted image showing recurrence of a multilobular ganglion cyst (asterisk) involving the tibial division (arrow) of the sciatic nerve. With piriformis muscle resection in the first surgery, type B variation is no longer observed. The line in the inset shows the level at which the corresponding coronal image was taken. (D) Coronal maximal intensity projection image taken 12 mm ventral to the level of Fig. 4C, showing the articular branch (arrow) of the ganglion cyst extending along the posterior acetabulum toward the paralabral cyst (arrowhead). The line in the inset shows the level at which the corresponding coronal image was taken. (E) A sagittal T2-weighted image showing recurrence of the ganglion cyst (asterisk) of the sciatic nerve (arrows). The line in the inset shows the level at which the corresponding sagittal image was taken. (F) Sagittal T2-weighted image taken 14 mm lateral at the level of Fig. 4E, showing the articular branch of the ganglion cyst (arrow) originating from the paralabral cyst (arrowhead) of the right hip joint.

Fig. 7.

Fig. 7.

Intraoperative images during reoperation for sciatic nerve adhesion due to recurrence of the ganglion cyst. (A) Intraoperative photograph showing the ganglion cyst (arrows) firmly adherent to the ventral side of the tibial division of the sciatic nerve tibial division of the sciatic nerve (TdSN). It looked the same as it did at the time of the first operation Fig. 4A. (B) Intraoperative photograph showing dissection and removal of the proximal portion (white arrows) of the articular branch (black arrows) rising between the gemellus muscle and the acetabulum to prevent recurrence of the ganglion cyst. (C) Intraoperative photograph showing completed dissection and removal of the proximal portion of the articular branch (black arrow) with circumferential decompression of the sciatic nerve. The path by which the articular branch travels from the ventral aspect of the gemellus muscle to the sciatic nerve was dissected. (D) T2-weighted coronal image taken 5 days after surgery, again showing the disappearance of the cyst with decompression of the sciatic nerve (black arrow). However, the proximal pathway (white arrow) of the articular branch remained present. The white arrowhead shows where the articular branch was removed. The line in the inset shows the level at which the corresponding coronal image was taken. (E) Sagittal T2-weighted image showing persistence of the proximal portion (white arrow) of the ganglion cyst. The degree of dissection of articular branches (white arrowhead) is noted ventral to the gemellus muscle (black arrowhead). The black arrow indicates the decompressed sciatic nerve. PdSN: peroneal division of the sciatic nerve; SN: the sciatic nerve.