MRI features of benign peripheral nerve sheath tumors: how do sporadic and syndromic tumors differ?

OBJECTIVES: To compare MRI features of sporadic and neurofibromatosis syndrome-related localized schwannomas and neurofibromas. METHODS: In this retrospective study, our pathology database was searched for "neurofibroma" or "schwannoma" from 2014 to 2019. Exclusion criteria were lack of available MRI and intradural or plexiform tumors. Qualitative and quantitative anatomic (location, size, relationship to nerve, signal, muscle denervation) and functional (arterial enhancement, apparent diffusion-weighted coefficient) MRI features of sporadic and syndrome-related tumors were compared. Statistical significance was assumed for p < 0.05. RESULTS: A total of 80 patients with 64 schwannomas (sporadic: 42 (65.6%) v. syndrome-related: 22 (34.4%)) and 19 neurofibromas (sporadic: 7 (36.8%) v. syndrome-related: 12 (41.7%)) were included. Only signal heterogeneity (T2W p=0.001, post-contrast p=0.03) and a diffused-weighted imaging target sign (p=0.04) were more frequent with schwannomas than neurofibromas. Sporadic schwannomas were similar in size to syndrome-related schwannomas (2.9±1.2cm vs. 3.7±3.2 cm, p = 0.6), but with greater heterogeneity (T2W p = 0.02, post-contrast p = 0.01). Sporadic neurofibromas were larger (4.6±1.5cm vs. 3.4±2.4 cm, p = 0.03) than syndrome-related neurofibromas, also with greater heterogeneity (T2W p=0.03, post-contrast p=0.04). Additional tumors along an affected nerve were only observed with syndrome-related tumors). There was no difference in apparent diffusion coefficient values or presence of early perfusion between sporadic and syndrome-related tumors (p > 0.05). CONCLUSIONS: Although syndrome-related and sporadic schwannomas and neurofibromas overlap in their anatomic, diffusion and perfusion features, signal heterogeneity and presence of multiple lesions along a nerve are differentiating characteristics of syndrome-related tumors.

Plexiform neurofibroma (Hamartoma) of the median nerve: A two-case report.

Plexiform neurofibroma is a benign peripheral nerve-sheath tumor, rarely involving major nerves of the extremities. In the literature, there are no clear treatment strategies for plexiform neurofibroma of major peripheral nerves. Our experience encountered two patients with plexiform neurofibroma of the median nerve, presenting with a palmar mass and symptoms of carpal tunnel compression. Preoperatively, plexiform neurofibroma was diagnosed on MRI and clinical examination. Both patients also experienced significant neurological deterioration, with finger numbness and increased nerve/tumor size. Potential malignant transformation was also considered. For these reasons, resection of the involved area of the nerve and repair were indicated. In both patients, intraoperative pathological diagnosis was plexiform neurofibroma. The 45-year-old male patient refused further surgery after carpal tunnel release, which was performed under axillary block. One year postoperatively, nerve compression symptoms decreased moderately. In the other patient, a 7-year-old boy, a significantly enlarged area of the median nerve was resected, and neurorrhaphy was performed. One year postoperatively, median nerve motor-sensory functions recovered completely. Four years postoperatively, no enlargement of the residual tumor was observed.

Differentiation of Peripheral Nerve Tumors in the Brachial Plexus.

Schwannomas are benign extracranial nerve sheath tumors that can rarely affect the brachial plexus. Due to the relative rarity of these tumors and the complexity of the anatomy of the neck and shoulder, these tumors are a challenging diagnosis for clinicians. We present a case report of a 51-year-old male with a brachial plexus schwannoma definitively treated with surgical resection. It is our hope that this case serves as a reminder to consider schwannomas in the differential diagnosis for infraclavicular tumors.

Monophasic synovial sarcoma mimicking schwannoma: a case report of a rare peripheral nerve tumor and literature review.

INTRODUCTION: Synovial sarcomas occurring as primary nerve tumors (SSPN) are rare and only 69 cases of SSPNs are reported in literature. Despite the little data available, SSPNs differ from other SSs in some distinctive aspects such as epidemiology, location, and early onset of symptoms. SSPN are consequently underdiagnosed and easily mistaken for benign or malignant peripheral nerve sheath tumors (PNST). Therefore, cytogenetic or molecular testing becomes essential in order to make a correct diagnosis. This article deals with an extremely rare case of monophasic SSPN of the posterior cords of the right brachial plexus. To our knowledge, this is only the tenth case of intraneural synovial sarcoma involving the brachial plexus. CASE PRESENTATION: We report the case of a 64-year-old man, who came to our attention due to a slow-growing painful right axillary neoformation, approximately 25 mm in size. The patient did not show any neurological impairments. Ultrasonography and constrast MRI showed a heterogeneous mass arising from the posterior cord of the right brachial plexus, resembling a schwannoma. The patient underwent total resection of tumor and capsule. Histologically, a diagnosis of monophasic synovial sarcoma was made based on histologic features and the immunohistochemical profile. CONCLUSIONS: We report a rare primary synovial sarcoma of the brachial plexus. Given its rarity, the diagnosis may be challenging and requires a core biopsy or the surgical specimen to permit immune-molecular analysis. Margin-free surgery is the mainstay of curative treatment, while chemo- or radiotherapy may have a role in advanced or margin-positive neoplasms.

Ultrasound and MR imaging of peripheral nerve tumors: the state of the art.

Peripheral nerve sheath tumors are a heterogeneous subgroup of soft tissue tumors that either arise from a peripheral nerve or show nerve sheath differentiation. On imaging, direct continuity with a neural structure or location along a typical nerve distribution represents the most important signs to suggest the diagnosis. Ultrasound and magnetic resonance imaging are the best modalities to evaluate these lesions. First, it is necessary to differentiate between a true tumor and a non-neoplastic nerve condition such as a neuroma, peripheral nerve ganglion, intraneural venous malformation, lipomatosis of nerve, or nerve focal hypertrophy. Then, with a combination of clinical features, conventional and advanced imaging appearances, it is usually possible to characterize neurogenic tumors confidently. This article reviews the features of benign and malignant peripheral nerve sheath tumors, including the rare and recently described tumor types. Furthermore, other malignant neoplasms of peripheral nerves as well as non-neoplastic conditions than can mimick neurogenic tumor are herein discussed.

Benign Neurogenic Tumors.

Neurogenic tumors arise from cells of the nervous system. These tumors can be found anywhere along the distribution of the sympathetic and parasympathetic nervous system and are categorized based on cell of origin: ganglion cell, paraganglion cell, and nerve sheath cells. Ganglion cell-derived tumors include neuroblastomas, ganglioneuroblastomas, and ganglioneuromas. Paraganglion cell-derived tumors include paragangliomas and pheochromocytomas. Nerve sheath cell-derived tumors include schwannomas (neurilemmomas), neurofibromas, and neurofibromatosis. Most of these are benign; however, they can cause local compressive symptoms. Surgery is the mainstay of treatment, if clinically indicated. Nonetheless, a thorough preoperative workup is essential, especially for catecholamine-secreting tumors.

Magnetic Resonance Imaging of Nerve Tumors.

Nerve tumors are uncommon soft tissue neoplasms predominantly arising from peripheral nerve sheath and Schwann cells. We review the manifestations of benign peripheral nerve sheath tumors, concentrating on distinguishing imaging features of schwannomas versus neurofibromas with an emphasis on treatment implications. Nevertheless, there is often an overlap between the imaging presentation of these two conditions, making the accurate radiologic diagnosis challenging. Therefore, tissue sampling is often needed for a definitive histologic diagnosis. Treatment planning largely depends on symptoms, location of the lesion, and underlying risk factors. Three major syndromes, neurofibromatosis type 1, type 2, and schwannomatosis, predispose patients to peripheral nerve sheath tumors (PNSTs), with particular concern about the malignant subtype expression. In patients with suspected PNSTs, correlation of imaging findings with clinical findings and genetic tests is helpful for a more accurate diagnosis and disease management. Some imaging features on magnetic resonance imaging and fluorodeoxyglucose-positron emission tomography can be helpful to differentiate malignant from benign subtypes.

Paraganglioma of the cauda equina: A clinicopathologic study of 12 cases with demonstration of cytokeratin positivity.

Paragangliomas are rare neuroendocrine tumors originating from neural crest-derived paraganglion cells. Primary cauda equina paraganglioma (CEP) pose both diagnostic and surgical challenges. We report 12 cases of CEP to characterize the diagnostic and operative approach to these rare tumors. 12 cases with primary CEP were studied; 5 patients were male (41.7%) and 7 were female (56.3%). The median age was 44 years (range: 15-64 years). The most common symptom was lower back pain of variable duration. Radiologically, the lesions were intradural and extramedullary with well-defined margins, and ranged from 1 to 4.5 cm. in diameter (mean: 1.65 cm). 9 tumors were composed of sheets and nests of cells with a neuroendocrine pattern and intense vascularity and displayed a characteristic Zellballen pattern. Interestingly, CAM 5.2 was diffusely or focally positive with a dot-like or membrane pattern in 8/11 cases (72.7%). Similarly, CK was diffusely or focally positive with membrane and cytoplasmic staining or with a dot-like pattern in 7/11 (63.6%) and 2/11 cases (18.2%). None of the cases showed deletion of SDHB nor expression of GATA3. CEP can display aberrant keratin positivity, and this should be considered in the differential diagnosis of these lesions. This finding also raises the possibility that CEP may be an entirely different entity than non-spinal paragangliomas.

Establishment and characterization of NCC-MPNST6-C1: a novel patient-derived cell line of malignant peripheral nerve sheath tumors.

Malignant peripheral nerve sheath tumors (MPNSTs) are a rare subtype of mesenchymal tumors that arise from the sheath of peripheral nerves. MPNSTs exhibit strong metastatic potential, leading to poor clinical outcomes. The clinical utility of radiation therapy and chemotherapy is marginal with respect to overall survival and effective systematic therapies for MPNSTs are still needed to improve patient outcome. Although patient-derived cell lines are an essential tool for the development of novel therapies, only a limited number of cell lines have been reported and are available from cell banks. Thus, we established the novel MPNST cell line, NCC-MPNST6-C1, using surgically resected MPNST tissue. The NCC-MPNST6-C1 cells retained copy-number alterations similar to those of the original tumors and demonstrated constant proliferation, spheroid formation, and invasion capability in vitro, which reflected the malignant features of the original tumor tissue. While the NCC-MPNST6-C1 cells did not exhibit tumorigenesis in nude mice, their use in drug screening resulted in anti-cancer agents with low IC50 values. Hence, we conclude that the NCC-MPNST6-C1 cell line is a useful resource for the study of MPNSTs.

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 ß-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.

Nerve capping treatment using a bioabsorbable nerve conduit with open or closed end for rat sciatic neuroma.

BACKGROUND AND AIMS: Nerve capping treatment using bioabsorbable nerve conduits has recently been introduced for painful amputation neuroma. However, no clinical or experimental data are available for comparing nerve conduits with open distal ends and closed distal ends. Here, we investigated the nerve conduit with open or closed distal ends as the superior capping device, using a commercially available polyglycolic acid (PGA) nerve conduit in a rat sciatic nerve amputation model. METHODS: Ninety-one rats were assigned to three groups: no-capping (n = 30), capping the resected nerve stump with open ends (n = 31), and closed-end nerve conduits (n = 30). Twelve weeks after sciatic neurectomy, with or without capping, the evaluation of neuropathic pain using the autotomy score was performed. Stump neuromas with perineural scars and neuroinflammation were evaluated histologically. RESULTS: The mean autotomy scores in the closed-end nerve conduit group were significantly lower than those in the no-capping group. However, the difference between the open-end nerve conduit and the closed-end nerve conduit groups was insignificant. Histologically, distal axonal fibers expanded radially and formed neuromas in the no-capping group while they were terminated within the PGA conduit in both capping groups. In particular, the closed-end version of the PGA nerve conduit blocked scarring from intruding through the open end and protected the nerve stump with less neuroinflammation. Nerve capping with the closed-end version of the PGA nerve conduit most effectively suppressed perineural neuroinflammation and scar formation around the resected nerve stump. INTERPRETATION: Nerve capping with the PGA nerve conduit, particularly those with closed ends, after rat sciatic neurectomy prevented amputation neuroma and relieved neuropathic pain.

A novel mechanism for the formation and propagation of neural tumors and lesions through neural highways.

By recognizing anatomic and radiologic patterns of rare and often misdiagnosed peripheral nerve tumors/lesions, we have defined mechanisms for the propagation of neural diseases. The novel concept of the nervous system serving as a complex system of "highways" driving the neural and perineural spread of these lesions is described in three examples: Intraneural dissection of joint fluid in intraneural ganglion cysts, perineural spread of cancer cells, and dissemination of unknown concentrations of neurotrophic/inhibitory factors for growth in hamartomas/choristomas of nerve. Further mapping of these pathways to identify the natural history of diseases, the spectrum of disease evolution, the role of genetic mutations, and how these neural pathways interface with the lymphatic, vascular, and cerebrospinal systems may lead to advances in targeted treatments.

Enhancer reprogramming in PRC2-deficient malignant peripheral nerve sheath tumors induces a targetable de-differentiated state.

Malignant peripheral nerve sheath tumors (MPNSTs) are soft tissue sarcomas that frequently harbor genetic alterations in polycomb repressor complex 2 (PRC2) components-SUZ12 and EED. Here, we show that PRC2 loss confers a dedifferentiated early neural-crest phenotype which is exclusive to PRC2-mutant MPNSTs and not a feature of neurofibromas. Neural crest phenotype in PRC2 mutant MPNSTs was validated via cross-species comparative analysis using spontaneous and transgenic MPNST models. Systematic chromatin state profiling of the MPNST cells showed extensive epigenomic reprogramming or chromatin states associated with PRC2 loss and identified gains of active enhancer states/super-enhancers on early neural crest regulators in PRC2-mutant conditions around genomic loci that harbored repressed/poised states in PRC2-WT MPNST cells. Consistently, inverse correlation between H3K27me3 loss and H3K27Ac gain was noted in MPNSTs. Epigenetic editing experiments established functional roles for enhancer gains on DLX5-a key regulator of neural crest phenotype. Consistently, blockade of enhancer activity by bromodomain inhibitors specifically suppressed this neural crest phenotype and tumor burden in PRC2-mutant PDXs. Together, these findings reveal accumulation of dedifferentiated neural crest like state in PRC2-mutant MPNSTs that can be targeted by enhancer blockade.

Brachial plexus tumors extending into the cervicothoracic spine: a review with operative nuances and outcomes

Background The rarity and anatomical complexity of brachial plexus tumors (BPTs) impose many challenges onto surgeons performing surgical resections, especially when these tumors invade the cervicothoracic spine. Treatment choices and surgery outcomes heavily depend on anatomical location and tumor type. Methods The authors performed an extensive review of the published literature (PubMed) focusing on “brachial plexus tumors” that identified invasion of the cervicothoracic spine. Result The search yielded 2774 articles pertaining to “brachial plexus tumors”. Articles not in the English language or involving cervicothoracic spinal invasion were excluded. Conclusions Recent research has shown that the most common method used to resect tumors of the proximal roots is the dorsal subscapular approach. Despite its association with high morbidity rate, this technique offers excellent exposure to the spinal roots and intraforaminal portion of the spinal nerve. The dorsal approach is used to resect recurrent lower trunk tumors and dumbbell-shaped neurofibromas, yet it is also the least common overall approach used in brachial plexus tumor resections. The ventral or anterior technique is commonly used to resect tumors at the cord to division level, and root to trunk level. Motor complications, transient nerve palsy, and bleeding are among the most common complications of the anterior supraclavicular approach. Further controlled studies are needed to fully determine the optimal surgical approach used to obtain the best outcomes and least complications for each type of brachial plexus tumor (AU)