Neuromuscular Choristoma Research Articles

Progressive Unilateral Foot Drop in a Child due to Neuromuscular Choristoma.

An 8.5-year-old boy presented with a history of progressive unilateral foot drop. A contrast magnetic resonance imaging of the pelvic girdle and the lumbosacral plexus revealed a diffuse fusiform thickening of the right lumbosacral trunk and the sciatic nerve in the intrapelvic and gluteal regions, with findings characteristic of a choristoma. Clinical and radiologic features as well as complications of this unusual entity are described.

Clinicopathological and molecular genetic features of neuromuscular choristoma-associated desmoid type fibromatosis

Objective: To investigate the clinicopathological and genetic characteristics of neuromuscular choristoma-associated desmoid type fibromatosis (NMC-DF). Methods: The clinical morphological and immunohistochemical features of 7 NMC-DF cases diagnosed from January 2013 to January 2023 in Beijing Jishuitan Hospital were retrospectively analyzed. A series of neuromuscular choristoma and neuromuscular choristoma-associated desmoid type fibromatosis were evaluated for CTNNB1 mutations, and hotspot mutations for CTNNB1 were tested in 4 NMC-DF cases using Sanger sequencing. Results: The tumors were collected from 3 females and 4 males, aged 1 to 22 years (mean 7.1 years), involving the sciatic nerve (n=4), brachial plexus (n=2) or multiple nerves (n=1). The course of the disease spanned from 3 months to 10 years. Two cases were recurrent tumors. All the 7 NMC cases showed endoneurial intercalation of mature skeletal muscle fibers among the peripheral nerve fascicles, and the histologic features of the NMC-DF were strikingly similar to the conventional desmoid-type fibromatosis. By immunohistochemistry, all NMC and NMC-DF cases showed aberrant nuclear staining of β-catenin (7/7), the muscle cells in NMC were intensely immunoreactive for desmin, and the admixed nerve fibers were highlighted by NF and S-100 (7/7). Four NMC and NMC-DF had CTNNB1 mutations, 3 c.121A>G (p.T41A) and 1 c.134C>T (p.S45F). Follow-up of the 7 cases, ranging from 22 to 78 months, showed tumor recurrence in 2 patients at 3 and 8 months respectively after the first surgical resection, of which 1 patient underwent above-knee amputation. No recurrence occurred in other cases with tumor excision and neurological reconstruction surgery. There was no metastasis occurred in the 7 cases. Conclusions: NMC is a rare congenital lesion with differentiated mature skeletal muscle tissue found in peripheral nerve fascicles, and approximately 80% of patients with NMC develop a soft tissue fibromatosis. CTNNB1 mutation in the Wnt signaling pathway may be involved in the pathogenesis of NMC and NMC-DF, and S45F mutations seems to have a higher risk of disease progression.

Adult neuromuscular choristoma, a rare peripheral nerve pathology: illustrative case.

Neuromuscular choristomas (NMCs) are rare tumors involving aberrant intercalation of muscle fibers into peripheral nerves, most commonly the sciatic nerve. Although benign, these lesions risk developing into NMCs with desmoid-type fibrosis (NMC-DTFs), aggressive lesions potentially requiring amputation. Currently, information on NMCs and the link between NMCs and NMC-DTFs is limited in adults, with the majority of cases reported in children. We present the case of a 66-year-old male with a sciatic NMC alongside a Preferred Reporting Items for Systematic Reviews and Meta-Analyses-based systematic review of similar cases to better characterize this lesion in the adult population. A male presented with 10 years of progressive left lower-extremity weakness and paresthesia, and a mildly enlarged proximal sciatic nerve was discovered on magnetic resonance imaging. He underwent left sciatic fascicular nerve biopsy, with histopathological examination identifying the lesion as an NMC. The literature review revealed that our case, alongside other cases of adults with NMCs, shared characteristics similar to NMCs in the pediatric population. More comprehensive studies of adults with NMCs are needed, as the current literature contains limited information concerning disease course, diagnostic characteristics, and treatment. Furthermore, NMCs in adults should be handled with care because of the increased likelihood of transformation to NMC-DTF after surgical intervention.

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

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. 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). 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.

Neuromuscular choristoma and circumferential nerve territory desmoid-type fibromatosis: imaging findings supporting a nerve-driven mechanism.

Neuromuscular choristoma (NMC) is a rare developmental malformation of peripheral nerve that is frequently associated with the development of a desmoid-type fibromatosis (DTF). Both NMC and NMC-DTF typically contain pathogenic CTNNB1 mutations and NMC-DTF develop only within the NMC-affected nerve territory. The authors aimed to determine if there is a nerve-driven mechanism involved in the formation of NMC-DTF from the underlying NMC-affected nerve. Retrospective review was performed for patients evaluated in the authors' institution with a diagnosis of NMC-DTF in the sciatic nerve (or lumbosacral plexus). MRI and FDG PET/CT studies were reviewed to determine the specific relationship and configuration of NMC and DTF lesions along the sciatic nerve. Ten patients were identified with sciatic nerve NMC and NMC-DTF involving the lumbosacral plexus, sciatic nerve, or sciatic nerve branches. All primary NMC-DTF lesions were located in the sciatic nerve territory. Eight cases of NMC-DTF demonstrated circumferential encasement of the sciatic nerve, and one abutted the sciatic nerve. One patient had a primary DTF remote from the sciatic nerve, but subsequently developed multifocal DTF within the NMC nerve territory, including 2 satellite DTFs that circumferentially encased the parent nerve. Five patients had a total of 8 satellite DTFs, 4 of which abutted the parent nerve and 3 that circumferentially involved the parent nerve. Based on clinical and radiological data, a novel mechanism of NMC-DTF development from soft tissues innervated by NMC-affected nerve segments is proposed, reflecting their shared molecular genetic alteration. The authors believe the DTF develops outward from the NMC in a radial fashion or it arises in the NMC and wraps around it as it grows. In either scenario, NMC-DTF develops directly from the nerve, likely arising from (myo)fibroblasts within the stromal microenvironment of the NMC and grows outward into the surrounding soft tissues. Clinical implications for patient diagnosis and treatment are presented based on the proposed pathogenetic mechanism.

Adult Neuromuscular Choristoma in the Intraconal Region of the Orbital Muscle: A Case Report

Adult Neuromuscular Choristoma in the Intraconal Region of the Orbital Muscle: A Case Report

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

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. 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. 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. 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 asthe 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.

Unrecognized neuromuscular choristoma with recurrent desmoid-type fibromatosis and Marjolin ulcer: expanding the spectrum of neuromuscular choristoma sequelae within the nerve territory? Illustrative case.

Neuromuscular choristoma (NMC) is a rare congenital lesion in which muscle tissue is admixed with nerve fascicles within a peripheral nerve. Patients commonly present in early childhood with neuropathy, plexopathy, or chronic undergrowth in the distribution of the affected nerve. The authors present the case of a 35-year-old man with unrecognized neuromuscular NMC of the sciatic nerve, which resulted in recurrent, multicentric NMC-associated desmoid-type fibromatosis (NMC-DTF) within the nerve territory in association with a Marjolin ulcer, a cutaneous malignancy. Based on anatomical and pathophysiological findings described in this case report, the authors support the association between NMC-DTF and Marjolin ulcer.

Clinical features and ultrasound findings of a rare musculoskeletal system disease–neuromuscular choristoma

BackgroundNeuromuscular choristomas (NMCs), are extremely rare developmental lesions that, have been previously established associated with recurrent fibromatosis after surgery, leading to several operations or even amputation. However, reports on the ultrasound imaging features and clinical conditions of NMCs are rare. The purpose of this study is to describe the ultrasound features and clinical analysis of NMCs to provide suggestions to identify the optimal management strategy.MethodsFrom September 2020 to September 2021, 7 patients with a confirmed diagnosis of NMC who underwent ultrasound examination in our department were enrolled in our study. Physical examinations were performed to detect motor deficits, sensory deficits, neuropathic pain, limb undergrowth, muscular atrophy, cavus foot and bone dysplasia. Ultrasound imaging was performed and investigated both in affected nerves and neuromuscular choristomas associated desmoid-type fibromatosis (NMC-DTF). All patients had a definite history and regular follow-up. The clinical course, physical examinations, ultrasound features and pathologic results of NMC patients were analyzed.ResultsSeven patients with an average age of 7.0 ± 7.2 years (range: 2–22 years) were enrolled in our study. The affected nerves included the sciatic nerve (6 cases) and the brachial plexus (1 case). Six patients (85.7%) presented with limb undergrowth, 6 (85.7%) with muscular atrophy, and 5 (71.4%) with cavus foot deformity. Based on ultrasound findings, all the visibly affected nerve segments presented with hypoechoic and fusiform enlargement with intraneural skeletal muscle elements. Five patients (71.4%) had NMC-DTFs at the site of the affected nerve. All NMC-DTFs were shown as hypoechoic solid lesions adjacent to the nerve and were well circumscribed. In the subset of the surgery group, all 5 patients presented with progression to NMC-DTFs at the site of the NMCs. No fibromatosis was detected in the other two nonsurgical patients.ConclusionsUnderstanding the typical ultrasound features and clinically associated conditions would support the early diagnosis of this rare disease. When a potential diagnosis is determined, an invasive procedure such as biopsy or resection might not be a good choice given the frequent occurrence of complications such as aggressive recurrence.

Lipomatosis of Nerve and Neuromuscular Choristoma: Two Rare Entities and Their Call for an Animal Model to Understand and Mitigate Nerve-Territory Sequelae

Two rare congenital nerve conditions (lipomatosis of nerve (LN) and neuromuscular choristoma (NMC)) share certain commonalities (hypertrophic fusiform lesions, often presenting with neuropathy in adolescent ages and an association with other lesions), but also have important clinical differences (nerve-territory overgrowth and undergrowth, respectively). LN is part of a spectrum of adipose tissue proliferations that affect nerves. NMCs, previously known as benign Triton tumors, are lesions in which mature skeletal muscle is admixed with nerve fascicles. Recent advances have led to the description of classic clinicoradiologic features and the identification of distinct genetic alterations in LN and NMC, that have direct clinical implications and present potential research opportunities for these and other related conditions.

Neuromuscular Choristoma: Report of Five Cases With CTNNB1 Sequencing.

Neuromuscular choristoma (NMC) are lesions of the peripheral nervous system characterized by an admixture of skeletal muscle fibers and nerves fascicles that are frequently associated with desmoid fibromatosis (DF). Mutations in CTNNB1, the gene for β-catenin protein, are common in DF and related to its pathogenesis. They are restricted to exon 3, with 3 point mutations: T41A, S45F, and S45P. To understand the pathogenesis of NMC, we tested CTNNB1 status in 5 cases of NMC whether or not they were associated with DF. The screening of mutations in CTNNB1 gene was based on amplicon deep sequencing using the ION Proton platform. Three patients had the S45F mutation; in 2 the mutation was common to both lesions and in one the DF was wild type while the NMC had the S45F mutation. One patient had a T41A mutation in the NMC and no associated DF. In the last patient, the DF lesion had a T41A mutation; there was no lesion with the S45P mutation. The presence of similar CTNNB1 mutations in NMC/DF-associated lesions and sporadic DF reinforces the relationship between both lesions and points to a common pathogenic mechanism.

Trigeminal Nerve Choristoma- A Rare Case Report

Choristomas are normal tissue in an abnormal location and are classified based on their predominant epithelial lining. They may contain fibrous tissue, skeletal muscle fibres, and nerve fibres. Neuromuscular choristoma (benign triton tumour) is a rare tumour that involves a large nerve trunk. Involvement of the cranial nerves by this lesion is exceptional; trigeminal nerve involvement is even rarer. This is a very rare case of intracranial trigeminal nerve neuromuscular choristoma which had an associated fatty component that also got ruptured, in a 30-year-old female who presented with a headache. The clinical presentation, radiological findings, pathological diagnosis for this case are discussed along with a review of the associated literature.

Nerve Encrusted Sinew - Benign Triton Tumour

Tumours categorized as generic admixture of neural tissue and skeletal tissue are benign triton tumour, neurofibroma and commonly discerned rhabdomyosarcoma. Benign triton tumour is an exceptional, developmental lesion comprised of commingled mature skeletal muscle tissue and mature neural tissue. The neoplasm is additionally nomenclated as “neuromuscular hamartoma” or “neuromuscular choristoma” “Triton” terminology is a derivative of amphibian triton salamander wherein normal nerve can induce regeneration of skeletal muscle.

Nerve Encrusted Sinew - Benign Triton Tumour

Tumours categorized as generic admixture of neural tissue and skeletal tissue are benign triton tumour, neurofibroma and commonly discerned rhabdomyosarcoma. Benign triton tumour is an exceptional, developmental lesion comprised of commingled mature skeletal muscle tissue and mature neural tissue. The neoplasm is additionally nomenclated as “neuromuscular hamartoma” or “neuromuscular choristoma” “Triton” terminology is a derivative of amphibian triton salamander wherein normal nerve can induce regeneration of skeletal muscle. Initially scripted by Louhimo and Rapola in 1972, benign triton tumour was documented as a hamartoma. Neuromuscular choristoma was a terminology adopted by Bonneau and Brochu as skeletal muscle fibres are not contemplated to be normal anatomic articulations of peripheral nerves(1,2). Simple observation and cogent tissue sampling is appropriate for diagnosis of the biologically benign neoplasm.

Vertical restrictive strabismus associated with proptosis: Similar clinical signs, different etiopathogenetic causes. A report of three patients.

To report the different uncommon pathogenesis of three cases of severe vertical restrictive strabismus associated with progressive unilateral proptosis with similar clinical features. Case series of three patients who presented to the Orbit Outpatient Service of Policlinico Gemelli with a history of left progressive unilateral proptosis, slowly worsening vertical strabismus and the left eye fixed in downward position. A thorough hematologic work up was performed. All patients underwent complete abdomen ultrasonography, orbital contrast enhanced magnetic resonance imaging, forced duction test under general anesthesia, and orbital biopsy. Patients were 30, 60, and 46 years old respectively. MRI showed left inferior rectus enlargement in two cases and superior rectus enlargement in one case, with contrast enhanced combined muscle belly and tendon enlargement in all cases. Patients underwent forced duction test, muscle weakening (in two cases), and muscle biopsy with histopathologic examination. The superior rectus appeared infiltrated by an undifferentiated high-grade pleomorphic sarcoma, whereas the two inferior recti were positive for idiopathic orbital inflammatory disease with fibrosis areas and neuromuscular choristoma, respectively. Although proptosis and acquired vertical restrictive strabismus are most commonly associated with thyroid associated orbitopathy (TAO), they can also be a manifestation of many other conditions and the differential diagnosis can be particularly challenging. The three reported cases presented indeed with similar clinical features but had three distinct underlying orbital etiologies, two of which were extremely uncommon.

MR spectroscopy differences between lipomatosis of nerve and neuromuscular choristoma: a potential adjunctive diagnostic tool.

To describe differences between lipomatosis of nerve (LN) and neuromuscular choristoma (NMC) evaluated with MR spectroscopy (MRS). Eight patients were included in this prospective pilot study: three patients with LNs and five with NMCs. Single voxel PRESS MRS of the tumors were acquired with 3T MRI. MRS data were processed with LCModel version 6.3-1J using the internal "lipid-8" basis set. From individual lipid peak and water content measurements, total fatty acid molecules (TFAM), unsaturated fatty acid molecules (UFAM), and glycerol molecules (GM) were computed and analyzed, as well as ratios of UFAM/TFAM, TFAM/GM, and a fatty-acid chain-length index (CLI). The LN group included two men and one woman (average age 58.3years); the NMC group included two men and three women (average age 20.4years). Lipid composition analysis showed that LN had considerably more fat than NMC: TFAM: LN = 15.29 vs NMC = 7.14; UFAM: LN = 4.48 vs NMC = 2.63; GM: LN = 5.20 vs NMC = 1.02. Both tumors had a similar fraction of unsaturated fatty acids: UFAM/TFAM: LN = 0.29 vs NMC = 0.37. LN had the usual number of FA molecules/glycerol molecule, while NMC had considerably more: TFAM/GM: LN = 2.94 vs NMC = 6.98. Finally, average FA chains were longer in NMC: CLI: LN = 17.39 vs NMC = 22.55. Our analysis suggests measurable differences in the amount and composition of lipid in LN and NMC. While a larger, statistically powered study is needed, these initial findings may be helpful to properly diagnose ambiguous cases and thereby avoid surgical intervention such as biopsy.

Neuromuscular choristoma-associated desmoid-type fibromatosis: Establishing a nerve territory concept.

Desmoid-type fibromatosis (DTF) frequently arises in patients with neuromuscular choristoma (NMC). We hypothesize that NMC-associated DTF occurs in soft tissues innervated by the NMC-affected nerve, and arises from CTNNB1-mutated (myo) fibroblasts within or directly adjacent to the NMC. A retrospective review of patients treated at our institution was performed for patients with biopsy-confirmed diagnosis of NMC-DTF. Clinical presentation, physical examination, electrodiagnostic findings and radiological features (MR and FDG PET/CT images for each NMC-DTF) and pathologic re-review of available materials were analyzed. A literature review was also performed. Eight patients from our institution met the inclusion criteria. All patients presented with neuropathic symptoms and soft tissue or bone changes in the nerve territory innervated by the NMC. All MR images (N=8 cases) showed the characteristic features of NMC, and also showed direct contact between unifocal (N=5) or multifocal (N=3) DTF(s) and the NMC-affected nerve NMC. FDG PET/CT (N=2 cases) showed diffuse, increased FDG uptake along the entire affected nerve segment, contiguous with the FDG-avid DTF. In all cases, the DTFs arose in the soft tissues of the NMC-affected nerve's territory. No patient developed DTF at any other anatomic site. These data demonstrate that NMC-DTF arises solely within the NMC-affected nerve territory, and has direct contact with the NMC itself. Based on all these findings and the multifocality of NMC in several cases, we recommend imaging and surveillance of the entire NMC-affected nerve (from spine to distal extremity) to identify clinically-occult DTF in patients with NMC.

Recurrent desmoid-type fibromatosis associated with underlying neuromuscular choristoma.

Desmoid-type fibromatosis (DTF) presents a therapeutic dilemma. While lacking metastatic potential, it is a locally aggressive tumor with a strong propensity for occurrence near nerve(s) and recurrence following resection. In this study, the authors introduce the association of an occult neuromuscular choristoma (NMC) identified in patients with DTF. After experiencing a case of DTF found to have an occult NMC, the authors performed a retrospective database review of all other cases of biopsy-proven DTF involving the extremities or limb girdles in patients with available MRI data. Two musculoskeletal radiologists with expertise in peripheral nerve imaging reviewed the MRI studies of the eligible cases for evidence of previously unrecognized NMC. The initial case of a patient with an occult sciatic NMC is described. The database review yielded 40 patients with DTF-18 (45%) in the upper limb and 22 (55%) in the lower limb. Two cases (5%) had MRI findings of NMC associated with the DTF, one in the proximal sciatic nerve and the other in the proximal tibial and sural nerves. The coexistence of NMC may be under-recognized in a subset of patients with extremity DTF. This finding poses implications for DTF treatment and the likelihood of recurrence after resection or biopsy. Further study may reveal crucial links between the pathogenesis of NMC and DTF and offer novel therapeutic strategies.

Clinical and Magnetic Resonance Imaging Longitudinal Follow-up of Neuromuscular Choristomas

The natural history of growth and radiologic progression of neuromuscular choristomas (NMCs) remain unknown. The purpose of this study was to describe the radiologic growth pattern of NMCs and to determine how the pattern of growth relates to clinical progression. A retrospective review was performed for patients with a confirmed diagnosis of NMC and at least 2 years of radiologic (magnetic resonance imaging [MRI]) follow-up. Medical records, including physical examinations and radiologic studies, were reviewed in detail. The NMC length and transverse dimensions were compared between serial MRI examinations. Eleven patients with a mean radiologic follow-up time of 5.6 years (range 2-19 years) were identified. Motor deficits occurred in 10 patients (90%), sensory deficits in 5 patients (45%), and neuropathic pain in 4 (36%) patients. Eight patients (73%) presented with manifestations of limb undergrowth, 2 (18%) with congenital hip dysplasia, and 1 with a cavus foot deformity. Progression of motor and sensory deficits was observed in 5 (45%) and 1 (9%) patients, respectively. The maximal length and height of the NMC was significantly (P < 0.05) longer (initial 218 ± 118 mm vs. follow-up 270 ±135 mm) and larger (20 ± 10 mm vs. 24 ± 14 mm) on the follow-up scan. MRI demonstrated abnormalities that were in continuity along the longitudinal extent of the NMC. According to this small but relatively long-term follow-up cohort, the growth pattern of this lesion is slow but progressive. We found a longitudinal continuity pattern of growth in all MRI scans, often spanning a great distance.

Stimulation Contractility Gradient of a Neuromuscular Choristoma Within the Sciatic Nerve: 2-Dimensional Operative Video.

Neuromuscular choristoma (NMC) is a rare congenital nerve lesion that is classified by the presence of heterotopic muscle fibers intercalated within nerve fascicles.1 The presence of NMC typically causes progressive neuropathy and bony/soft tissue undergrowth, often leading to a shortened atrophic limb.2,3 The typical appearance of NMC on magnetic resonance imaging is an enlarged fusiform nerve that exhibits minimal gadolinium enhancement.4 While there is increasing documentation of pathognomonic clinical and radiographic features for various diffuse fusiform peripheral nerve lesions, nerve biopsy is still occasionally required for some patients given the rarity of these diseases and progressive neuropathic features.The intraoperative appearance of NMC and its unique electrical stimulation properties are quite interesting. Intrafascicular replacement of nerve by skeletal muscle gives the nerve a red beefy color and causes the fascicles to contract with electrical stimulation.5 In this video, we demonstrate the intraoperative appearance and contractile properties of NMC in a 60-yr-old woman with progressive sciatic neuropathy. Histologic and immunohistochemical studies identified a gradient of intralesional mature skeletal muscle within the NMC, with substantially fewer desmin-positive skeletal muscle fibers in the distal aspect. A gradient of contractility with intraoperative stimulation seemed to correlate with this pathology. These findings suggest that the lesional extent of NMC may not be clinically or grossly evident, reflecting a varying distribution of skeletal muscle within the affected nerve.The Mayo Clinic Institutional Review Board Office for Human Research Protection does not require approval for single participant case studies. The subject involved in this study was not identifiable and the general surgical consent form included permission for intraoperative photos and video.