Exuberant circumferential fibroproliferative neuromas in lipomatosis of nerve: a unifying theory. Illustrative case.

BACKGROUND: Lipomatosis of nerve (LN) is a rare disorder characterized by the massive enlargement of peripheral nerves, frequently accompanied by generalized fibroadipose proliferation and skeletal overgrowth. OBSERVATIONS: The authors have been routinely following a 20-year-old male for lipomatosis of median nerve at the wrist noted shortly after birth. He had undergone resection of the lesion accompanied by sural nerve grafting at another institution. Clinically, although his neurological loss of function has been stable, he has had continued soft tissue growth. Serial magnetic resonance imaging has revealed persistent LN proximal to the repair sites with evidence of fatty proliferation in the sural grafts and continued LN and fatty proliferation distally. There has been a progressive circumferential pattern of fibrosis around the proximal and distal suture lines, which has a similar radiological pattern to desmoid type fibromatosis (a pattern recently described in neuromuscular choristoma [NMC] desmoid-type fibromatosis). LESSONS: Considering the similar reaction of nerve in both LN and NMC despite differing genetic cascades, the authors believe a unifying process occurs in both lesions. The pattern of circumferential fibroproliferation would be most consistent with neuron-mediated growth from unspecified trophic factors, supporting a previously reported a nerve-derived "inside-out mechanism." The clinical consequences of this unifying process are presented.

What is new in intraneural perineurioma?

Since the initial description of intraneural (IN) perineurioma in 1964, advances in the understanding of the clinical presentation, diagnostic imaging, pathologic features, and genetic underpinnings have changed how this pathology is managed. IN perineuriomas are rare, benign peripheral nerve sheath tumors, most frequently coming to clinical attention when patients present with painless, progressive weakness or sensory loss in adolescence or young adulthood. The gold standard of diagnosis has traditionally been with targeted tissue biopsy demonstrating "pseudo-onion bulb" formation with positive epithelial membrane antigen (EMA) staining. However, modern magnetic resonance imaging is allowing some patients to forgo biopsy. Recent genetic studies of IN perineuriomas have demonstrated common TRAF7 point mutations and rare NF2 mutations, which may present targets for diagnosis or therapy in the future. Current advances have allowed for us to provide improved patient counseling with informed understanding for various clinical scenarios. With the workup and diagnosis now clearly defined, the next frontier is for improving the lives of patients with IN perineuriomas through the interaction between restoration of functional deficits and advances in our understanding of the genetics of this entity.

Tibial intraneural ganglion cysts arising from the tibiofemoral joint: illustrative cases.

BACKGROUND: Intraneural cysts involving the tibial nerve in the knee region (popliteal fossa) are rare. According to the articular (synovial) theory, which posits a joint origin for this pathology, these cysts originate from either the superior tibiofibular joint (STFJ) or the tibiofemoral (knee) joint. As tibial intraneural cysts arising from the tibiofemoral joint remain poorly understood, the authors present 2 illustrative cases and a review of the world's literature on all tibial intraneural ganglion cysts in the knee region. OBSERVATIONS: Fourteen cases of tibial intraneural ganglion cysts arising from the tibiofemoral joint were identified in the literature. Different articular branch patterns were demonstrated, which could be explained by the varied, rich articular branch innervation at the knee. Favorable outcomes were observed in cases in which the articular branch had been disconnected and the cyst drained and were comparable to the outcomes seen in tibial intraneural ganglion cysts with an STFJ origin. LESSONS: Tibial intraneural cysts in the knee region can be subdivided by their joint of origin: the STFJ or the tibiofemoral joint. Those arising from the tibiofemoral joint originate from different areas of the joint and propagate in predictable patterns, with favorable outcomes following surgical intervention when the joint connection is identified and treated. The origin of tibial intraneural cysts from the tibiofemoral joint are more complex than those originating from the STFJ but seem to have similar propagation patterns and outcomes.

Posterior interosseous nerve paralysis secondary to an extraneural ganglion cyst from a radial neck pseudarthrosis: illustrative case.

BACKGROUND: Many benign and malignant tissue or bony lesions have been reported as causes of extrinsic or intrinsic posterior interosseous nerve (PIN) neuropathy at the proximal forearm/elbow region. The authors describe an unusual cause of external compression of the PIN due to a ganglion cyst arising from a radial neck pseudarthrosis (a false joint). OBSERVATIONS: Decompression of the PIN with the release of the arcade of Frohse was performed with resection of the radial head and the ganglion cyst. By 6 months postoperatively, the patient had a complete neurological recovery. LESSONS: This case illustrates a previously unreported cause of extraneural compression of the PIN from a pseudarthrosis. The mechanism for compression in this case from the radial head pseudarthrosis is likely attributable to the sandwich effect, in which the PIN is sandwiched between the arcade of Frohse at the supinator from above and the cyst below.

7T for clinical imaging of benign peripheral nerve tumors: preliminary results.

PURPOSE: MRI has become an essential diagnostic imaging modality for peripheral nerve pathology. Early MR imaging for peripheral nerve depended on inferred nerve involvement by visualizing downstream effects such as denervation muscular atrophy; improvements in MRI technology have made possible direct visualization of the nerves. In this paper, we share our early clinical experience with 7T for benign neurogenic tumors. MATERIALS: Patients with benign neurogenic tumors and 7T MRI examinations available were reviewed. Cases of individual benign peripheral nerve tumors were included to demonstrate 7T MRI imaging characteristics. All exams were performed on a 7T MRI MAGNETOM Terra using a 28-channel receive, single-channel transmit knee coil. RESULTS: Five cases of four pathologies were selected from 38 patients to depict characteristic imaging features in different benign nerve tumors and lesions using 7T MRI. CONCLUSION: The primary advantage of 7T over 3T is an increase in signal-to-noise ratio which allows higher in plane resolution so that the smallest neural structures can be seen and characterized. This improvement in MR imaging provides the opportunity for more accurate diagnosis and surgical planning in selected cases. As this technology continues to evolve for clinical purposes, we anticipate increasing applications and improved patient care using 7T MRI for the diagnosis of peripheral nerve masses.

Tibial intraneural ganglion cysts at the superior tibiofibular joint treated with joint resection alone: a proof of concept.

BACKGROUND: Intraneural ganglion cysts involving the tibial nerve are rare. Recent evidence has supported an articular (synovial) theory to explain the joint-related origin of these cysts; however, optimal operative treatment for cysts originating from the STFJ remains poorly understood. Therefore, we present a novel strategy: addressing the joint itself without addressing the articular branch and/or the cyst. METHODS: Records of patients with tibial intraneural ganglion cysts with a connection to the STFJ who were treated with a joint resection alone at a single academic institution were reviewed. The clinicoradiographic features, operative intervention, and postoperative course were recorded. RESULTS: We identified a consecutive series of 7 patients. These patients (4/7 male, 57%) were 43 (range 34-61) years of age and all presented with symptoms of neuropathy. The patients underwent resection of the synovial surfaces of the STFJ without disconnection of the articular branch or decompression of the cyst. Postoperatively, three patients regained partial motor function (43%, n=7), although four patients noted continued sensory abnormality (57%, 4/7). All six patients with postoperative MRIs had some evidence of regression of the cyst. CONCLUSIONS: This novel surgical technique serves as a proof of concept-highlighting the fact that treating the primary source (the joint origin) can be effective in eliminating the secondary problem (the cyst itself). While this study shows that this simplified approach can be employed in select cases, we believe that superior results (faster, fuller recovery) can be achieved with combinations of disconnecting the articular branch, decompressing the cyst, and/or resecting the joint.

Characterizing peroneal nerve injury clinicoradiological patterns with MRI in patients with sciatic neuropathy and foot drop after total hip replacement.

OBJECTIVE: Sciatic nerve injury following total hip arthroplasty (THA) predominantly affects the peroneal division of the sciatic nerve, often causing a foot drop. This can result from a focal etiology (hardware malposition, prominent screw, or postoperative hematoma) or nonfocal/traction injury. The objective of this study was to compare the clinicoradiological features and define the extent of nerve injury resulting from these two distinct mechanisms. METHODS: Patients who developed a postoperative foot drop within 1 year after primary or revision THA with a confirmed proximal sciatic neuropathy based on MRI or electrodiagnostic studies were retrospectively reviewed. Patients were divided into two cohorts: group 1 (focal injury), including patients with an identifiable focal structural etiology, and group 2 (nonfocal injury), including patients with a presumed traction injury. Patient demographics, clinical examinations, subsequent surgeries, electrodiagnostic study results, and MRI abnormalities were noted. The Student t-test was used to compare time to onset of foot drop and time to secondary surgery. RESULTS: Twenty-one patients, treated by one surgeon, met inclusion criteria (8 men and 13 women; 14 primary THAs and 7 revision THAs). Group 1 had a significantly longer time from THA to the onset of foot drop, with a mean of 2 months, compared with an immediate postoperative onset in group 2 (p = 0.02). Group 1 had a consistent pattern of localized focal nerve abnormality on imaging. In contrast, the majority of patients in group 2 (n = 11) had a long, continuous segment of abnormal size and signal intensity of the nerve, while the other 3 patients had a segment of less abnormal nerve in the midthigh on imaging. All patients with a long continuous lesion had Medical Research Council grade 0 dorsiflexion prior to secondary nerve surgeries compared with 1 of 3 patients with a more normal midsegment. CONCLUSIONS: There are distinct clinicoradiological findings in patients with sciatic injuries resulting from a focal structural etiology versus a traction injury. While there are discrete localized changes in patients with a focal etiology, those with traction injuries demonstrate a diffuse zone of abnormality within the sciatic nerve. A proposed mechanism involves anatomical tether points of the nerve acting as points of origin and propagation for traction injuries, resulting in an immediate postoperative foot drop. In contrast, patients with a focal etiology have localized imaging findings but a highly variable time to the onset of foot drop.

Radial nerve myofibroma: a rare benign tumor with perineural infiltration. Illustrative case.

BACKGROUND: Myofibromas are benign mesenchymal tumors, classically presenting in infants and young children in the head and neck region. Perineural involvement, especially in peripheral nerves within the upper extremity, is extremely rare in myofibromas. OBSERVATIONS: The authors present the case of a 16-year-old male with a 4-month history of an enlarging forearm mass and rapidly progressive dense motor weakness in wrist, finger, and thumb extension. Preoperative imaging and fine needle biopsy confirmed the diagnosis of a benign isolated myofibroma. Given the dense paralysis, operative management was indicated, and intraoperative exploration showed extensive involvement of tumor within the radial nerve. The infiltrated nerve segment was excised along with the tumor, and the resulting 5-cm nerve gap was reconstructed using autologous cabled grafts. LESSONS: Perineural pseudoinvasion can be an extremely rare and atypical feature of nonmalignancies, resulting in dense motor weakness. Extensive nerve involvement may still necessitate nerve resection and reconstruction, despite the benign etiology of the lesion.

Perineurioma of the sciatic nerve with reticular, microcystic, and pseudolipoblastic features: illustrative case.

BACKGROUND: Perineuriomas are peripheral nerve sheath tumors that are composed of benign, localized proliferations of perineural cells and further subclassified as intraneural or extraneural (soft tissue) based on their relationship to the histological boundaries of the nerve. Multiple histological variants have been described, and herein the authors present the first known case of a pseudolipoblastic perineurioma affecting the nerve. OBSERVATIONS: A 52-year-old woman presented with a 5-year history of progressive, severe left buttock pain radiating down to the top of her foot and ankle, without any associated weakness, with a large mass in her sciatic nerve noted on magnetic resonance imaging (MRI). She underwent resection, which demonstrated a pseudolipoblastic perineurioma of the sciatic nerve, an unusual histological subtype composed of perineurial cells with an abundant clear intracytoplasmic background. Postoperatively, her pain resolved, and follow-up MRI showed no tumor persistence or recurrence. LESSONS: On imaging, this lesion had a benign appearance, with areas suggestive of subacute hemorrhage, and was associated with a nerve. Although the distinctive morphological features of this lesion may suggest liposarcoma, careful morphological evaluation and appropriate immunohistochemical studies allow its correct classification.

Nerve relationships to the sacrospinous ligament: application to suspension procedures and transgluteal approaches for nerve repair and tumor removal with three case illustrations.

BACKGROUND: Transvaginal suspension procedures often use the sacrospinous ligament (SSL), which attaches onto the ischial spine (IS). However, nerve-related sequelae (e.g., sciatic nerve injury) following such procedures have been reported. Therefore, the current anatomical study was performed to better understand these relationships. Additionally, three case illustrations of patients with injury to the sciatic nerve following sacrospinous ligament suspension procedures are included to exemplify the significance of a thorough knowledge of this anatomy. METHODS: In 20 human adult cadavers (40 sides), a gluteal dissection was performed to expose the IS and SSL and regional nerves near the greater sciatic foramen. Measurements between the IS and SSL were made between these structures and surrounding nerves. RESULTS: The average distance between the IS and sciatic nerve was 1.4 cm. From this bony part, the average distance to the S1 and S2 ventral rami was 3.1 cm and 1.9 cm, respectively. From the IS to the lumbosacral trunk, pudendal nerve, nerve to obturator internus, and superior gluteal nerve, the mean distance was 4 cm, 0.5 cm, 0.7 cm, and 4.5 cm, respectively. From the SSL to the lumbosacral trunk, S1 ventral ramus, and S2 ventral ramus, there was an average distance of 4.2 cm, 1.6 cm, and 0.8 cm, respectively. Statistically, in females, the distances from the IS and SSL to the sciatic nerve, lumbosacral trunk, superior gluteal nerve, and S1 and S2 ventral rami were shorter when compared to males. CONCLUSION: An improved understanding of the relationship between the SSL and IS and nerves near the greater sciatic foramen can lead to fewer intraoperative complications during approaches to various peripheral nerves in this region. Lastly, these relationships might help better understand the nerve injuries following pelvic suspension procedures that use the SSL.

PET imaging characteristics of neuromuscular choristoma and associated desmoid-type fibromatosis.

BACKGROUND: Neuromuscular choristoma (NMC) is a rare peripheral nerve lesion characterized by abnormal presence of muscle within nerve. Associated desmoid-type fibromatosis (NMC-DTF) often develops. We report 18F-fluorodeoxyglucose positron emission tomography (FDG PET) characteristics of NMC and NMC-DTF and propose that increased FDG activity within NMCs may be associated with subclinical NMC-DTF or NMC-DTF "precursor" tissue. METHODS: Our institutional database was searched for all NMC cases. Inclusion criteria were 1) confirmed diagnosis of NMC with or without biopsy, and 2) available PET and MRI studies. PET data included SUVmax and SUVmean of NMCs, contralateral limb normal skeletal muscle and unaffected nerves, and SUVmax of NMC-DTF if present. SUV values were compared using paired t-test. A p value of < 0.05 was considered statistically significant. RESULTS: Our cohort consisted of 9 patients with NMC, 8 cases involving sciatic nerve and 1 of brachial plexus. On PET imaging, all NMC-affected nerve segments showed significantly higher FDG uptake (SUVmax/mean) compared to both contralateral normal nerve and normal skeletal muscle (all P < 0.05). Similar to sporadic DTF, NMC-DTF was highly FDG-avid (average SUVmax of 4.2). SUVmax in NMC with or without concurrent NMC-DTF did not differ (p = 0.76). Within NMC-affected nerve segment, FDG activity was relatively higher in areas with low T1/T2 MR signal. CONCLUSION: All NMCs were more FDG avid compared to both normal skeletal muscle and contralateral unaffected nerve, arguing against the presence of heterotopic muscle in NMC as the source of FDG avidity. FDG avidity within NMC may reflect subclinical NMC-DTF or a precursor lesion, as NMC-DTF are highly FDG-avid, and the highest regions of FDG avidity in NMC occurred in regions with MR characteristics associated with NMC-DTF (i.e., lower T1/T2 signal). We believe that the integration of FDG PET with serial MR imaging in patient follow up will clarify its utility in both detection and surveillance of NMC-DTF.

Peroneal intraneural ganglion cyst with a nearly invisible joint connection (even to advocates of the articular theory): illustrative case.

BACKGROUND: The articular (synovial) theory describes the formation of intraneural ganglion cysts through defects in the capsule of synovial joints. While the articular theory is gaining significant traction in the literature, it is not universally accepted. Therefore, the authors present a case of a plainly visible peroneal intraneural cyst, although the subtle joint connection was not identified specifically at the time of surgery, with subsequent rapid extraneural cyst recurrence. The joint connection was not immediately evident on review of the magnetic resonance imaging, even to the authors who have a large experience with this clinical entity. The authors report this case to demonstrate that all intraneural ganglion cysts have joint connections, although they may be difficult to identify. OBSERVATIONS: An occult joint connection in the intraneural ganglion poses a unique diagnostic and management dilemma. High-resolution imaging is a valuable tool used to identify the articular branch joint connection as part of the surgical planning. LESSONS: Based on the articular theory, all intraneural ganglion cysts will have a joint connection through an articular branch, although this may be small or nearly invisible. Failure to appreciate this connection can lead to cyst recurrence. A high index of suspicion of the articular branch is needed for surgical planning.

Occult lipomatosis of the nerve as part of macrodystrophia lipomatosa: illustrative case.

BACKGROUND: Macrodystrophia lipomatosa (MDL) is characterized by progressive overgrowth affecting soft tissues and bony structures and is part of lipomatous overgrowth syndromes. MDL has been associated with lipomatosis of the nerve (LN), an adipose lesion of nerve that has a pathognomonic magnetic resonance imaging (MRI) appearance as well as a mutation in the PIK3CA gene. The authors present a case of occult LN in the setting of MDL. OBSERVATIONS: A 2-year-old boy with progressive soft tissue overgrowth of his proximal right lower extremity was initially diagnosed with neurofibromatosis type 1 (NF1). At our institution, NF1 as well as other overgrowth syndromes including PTEN hamartoma tumor syndrome were excluded. He was diagnosed as having so-called MDL. Upon reinterpretation of the patient's MRI studies, short-segment LN involving the proximal sciatic nerve and part of lumbosacral plexus was identified. He underwent 2 debulking/liposuction procedures for soft tissue overgrowth. Genetic testing of tissue revealed a mutation in PIK3CA. LESSONS: Thorough clinical examination (for signs of overgrowth) as well as an MRI study of the entire neural pathway is a critical part of the diagnostic workup to evaluate for LN. The authors believe that an increasing association of LN, even when occult, will emerge that will explain many cases with marked nerve-territory overgrowth.

Plexal intraneural perineurioma: an analysis of the clinicoradiologic presentation of this rare variant.

PURPOSE: Intraneural (IN) perineurioma is a rare benign peripheral nerve sheath tumor, typically presenting as a painless, progressive mononeuropathy in adolescents. A rare plexal variant has been described, although there are little data describing its clinicoradiologic features. Herein, we present the largest case series of plexal IN perineuriomas reported in the literature. METHODS: Electronic medical records (EMR) from 1990 to 2022 from a single academic institution were reviewed for a diagnosis of IN perineurioma involving the brachial or lumbosacral plexus. This identified 18 patients, of which 17 had available MR imaging. We reviewed the EMR for demographics, clinical presentation, imaging characteristics, and surgical outcomes. RESULTS: Eighteen patients were identified. Most patients were male (11/18, 61%) and first developed symptoms at the age of 9.6 years (range 7 months to 55 years). Diagnosis occurred on average at the age of 22 years (4-57 years), which is significantly earlier than distal IN perineurioma (p = 0.0096). All patients (100%, 17/17) presented with motor polyneuropathy and muscular atrophy in multiple nerve distributions, with associated sensory loss (12/17, 71%). Most plexal lesions occurred in the brachial plexus (66%, 12/18). Five (29%, 5/17) patients presented with a hand/foot discrepancy, and 5 patients (29%) had a limb length discrepancy. Five patients underwent tendon transfer, of which two had failure of tendon transfer at most recent follow-up (50%, 2/4) due to progression of neurologic loss affecting the donors. Of patients managed nonoperatively, 87% of patients (6/7) with follow-up information demonstrated disease progression with worsening motor function or sensory loss, and 2 patients demonstrated progression on imaging at most recent follow-up. CONCLUSIONS: Plexal perineurioma represents an uncommon variant of IN perineurioma that presents as a progressive motor and sensory polyneuropathy in childhood or early adolescence. Surgical management remains controversial, and tendon transfer tends to result in poor long-term surgical outcomes.

Hybrid tumors with perineurioma components: a systematic review of the literature and illustrative case.

PURPOSE: Hybrid peripheral nerve sheath tumors (HPNST) are a newly recognized class of peripheral nerve sheath tumor, composed of at least two areas characteristic of perineurioma, schwannoma, or neurofibroma. The literature consists only of case reports and small series; therefore, we present an illustrative case and an analysis of all reported cases of HPNST with a perineurioma component in the literature. METHODS: A systematic search of the literature was performed to identify all reported cases of hybrid perineurioma-schwannoma or perineurioma-neurofibroma in the world's literature. Individual cases were analyzed for demographics, clinical features, imaging, and outcomes. RESULTS: A total of 159 cases were identified across 41 studies. Hybrid tumors tended to present in mid-adulthood (median 38.5 years), predominantly affected females (57%, 89/156), as a painless (63%, 63/100) mass, or swelling. Ten patients (10/74, 14%) had a history of neurofibromatosis 1, and 2 patients a history of neurofibromatosis 2 (2/74, 3%). The majority (78%, 122/157) of cases occurred superficially, most commonly in the lower extremity (25%, 39/157). Perineurioma-schwannoma was the most reported (86%, 137/159) pathologic diagnosis, with 3 cases presenting with malignant features. Two cases reocurred after resection. CONCLUSION: HPNST tend to occur in mid-adulthood and present as slowly progressive, painless, superficial masses, with a heterogeneous appearance on imaging. These entities pose a unique diagnostic challenge and likely remain under-recognized in the literature and current clinical practice. They pose low risk of recurrence or malignant transformation, and future work regarding the association with neurofibromatosis and genetic profiles is needed.

The value of high-resolution imaging in an occult peroneal intraneural ganglion cyst: illustrative case.

BACKGROUND: Foot drop is a common complaint with a broad differential diagnosis making imaging a key part of the diagnostic workup. The authors present a patient with an occult peroneal intraneural ganglion cyst who underwent imaging with high-frequency ultrasound (US) and high-resolution magnetic resonance imaging (MRI) to highlight the role of such techniques in cases of peroneal neuropathy. OBSERVATIONS: Intraneural ganglion cysts are emerging as a common cause of common peroneal neuropathy. Imaging with US and MRI is a valuable tool used to illustrate the pertinent anatomy and identify the articular branch joint connection and cyst as part of the surgical planning and definitive management. LESSONS: Intraneural ganglion cysts can be small or nearly invisible and failure to appreciate the intraneural cyst can lead to symptom or cyst persistence or recurrence. High-resolution modalities can be useful in the diagnosis and surgical planning of difficult cases.

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

BACKGROUND: Advancements in imaging and an understanding of the pathomechanism for intraneural ganglion cyst formation have led to increased awareness and recognition of this lesion. However, the precise role of imaging has been advocated for but not formally evaluated. METHODS: We performed a systematic review of the world literature to study the frequency of imaging used to diagnose intraneural ganglion cysts at different sites and compared trends in identifying joint connections. RESULTS: We identified 941 cases of intraneural ganglion cysts, of which 673 had published imaging. Magnetic resonance imaging (MRI, n = 527) and ultrasonography (US, n = 123) were the most commonly reported. They occurred most frequently in the common peroneal nerve (n = 570), followed by the ulnar nerve at the elbow (n = 88), and the tibial nerve at the ankle (n = 58). A joint connection was identified in 375 cases (48%), with 62% of MRIs showing a joint connection, followed by 16% on US, and 6% on computed tomography (CT). MRI was statistically more likely to identify a joint connection than was US (P < 0.01). In the last decade, joint connections have been identified with increasing frequency using preoperative imaging, with up to 75% of cases reporting joint connections. CONCLUSIONS: Preoperative imaging plays an important role in establishing the diagnosis of intraneural ganglion cyst as well as treatment planning. Imaging has proved superior to the sole reliance of operative exposure to identify a joint connection, which is necessary to treat the underlying disease. Failure to identify cyst connections on imaging can result in an inability to truly address the underlying pathoanatomy at the time of definitive surgery, leading to a risk for clinical recurrence. Therefore, management should be guided by an intersection between new knowledge presented in the literature, clinical expertise, and surgeon experience.

Does complete regression of intraneural ganglion cysts occur without surgery?

PURPOSE: The dynamic nature of intraneural ganglion cysts, including spontaneous expansion and regression, has been described. However, whether these cysts can regress completely in the absence of surgical management has important therapeutic implications. Therefore, we aim to review the literature for cyst regression without surgical intervention. METHODS: We reviewed our database of 970 intraneural ganglion cysts in the literature to search for evidence of complete regression based on strict radiologic confirmation, either spontaneously, or after percutaneous cyst aspiration or steroid injection. RESULTS: We did not find any examples of complete regression without surgical treatment that met inclusion criteria. Spontaneous regression was reported in four cases; however, only two cases had follow-up imaging, both of which demonstrated residual cysts. Nineteen cases of percutaneous intervention were found in the literature, 13 of which reported clinical improvement following aspiration/steroid injection; however, only seven cases had available imaging. Only two cases reported complete resolution of cyst on MR imaging at follow-up, but reinterpretation found residual intraneural cyst in both cases. CONCLUSION: We believe that pathology (structural abnormalities and/or increased joint fluid) always exists at the joint origin of intraneural ganglion cysts which persist even with regression of the cyst. The persistence of a capsular abnormality or defect can lead to recurrence of the cyst in the future, and while imaging may show dramatic decreases in cyst size, truly focused assessment of images will show a tiny focus of persistent intraneural cyst at the joint origin. Thus, expectant management or percutaneous intervention may lead to regression, but not complete resolution, of intraneural ganglion cysts.