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Abstract Neoplasms of the peripheral nervous system represent a heterogenous group with a wide spectrum of morphological features and biological potential. They range from benign and curable by complete excision (schwannoma and soft tissue perineurioma) to benign but potentially aggressive at the local level (plexiform neurofibroma) to the highly malignant (malignant peripheral nerve sheath tumors [MPNST]). In this review, we discuss the diagnostic and pathologic features of common peripheral nerve sheath tumors, particularly those that may be encountered in the intracranial compartment or in the spine and paraspinal region. The discussion will cover schwannoma, neurofibroma, atypical neurofibromatous neoplasms of uncertain biological potential, intraneural and soft tissue perineurioma, hybrid nerve sheath tumors, MPNST, and the recently renamed enigmatic tumor, malignant melanotic nerve sheath tumor, formerly referred to as melanotic schwannoma. We also discuss the diagnostic relevance of these neoplasms to specific genetic and familial syndromes of nerve, including neurofibromatosis 1, neurofibromatosis 2, and schwannomatosis. In addition, we discuss updates in our understanding of the molecular alterations that represent key drivers of these neoplasms, including neurofibromatosis type 1 and type 2, SMARCB1, LZTR1, and PRKAR1A loss, as well as the acquisition of CDKN2A/B mutations and alterations in the polycomb repressor complex members (SUZ12 and EED) in the malignant progression to MPNST. In summary, this review covers practical aspects of pathologic diagnosis with updates relevant to neurosurgical practice.

Abstract 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.

BackgroundPerineural tumor spread (PNTS) to the brachial plexus (BP) is a rare and challenging condition. This study aimed to elucidate the clinical presentations, diagnostic challenges, and outcomes of patients with PNTS to the BP.MethodsWe retrospectively reviewed patients diagnosed with PNTS to the BP at our institution between January 2009 and June 2024. Clinical characteristics, magnetic resonance imaging (MRI), 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) findings, and treatment outcomes were analyzed.ResultsSeven patients (mean age, 50.3 years) were identified. The primary cancer diagnoses included invasive ductal carcinoma of the breast (n = 3), metaplastic carcinoma of the breast (n = 1), lung adenocarcinoma (n = 2), and papillary thyroid carcinoma (n = 1). The median time from the initial cancer diagnosis to PNTS symptom onset was 71.0 months. All patients initially presented with progressive unilateral pain or paresthesia, followed by motor weakness. Lower trunk plexopathy was the most common electrodiagnostic finding (n = 5). In most patients, BP MRI showed diffuse tubular enlargement and T2 hyperintensity throughout the BP (n = 6), with gadolinium enhancement primarily in the proximal regions (n = 7). 18F-FDG PET/CT demonstrated increased uptake in the BP, most prominently at the cervical spinal root or trunk levels (n = 6). Despite treatment, neurological outcomes were generally poor. Six of the seven patients died after a median follow-up of 19 months post-PNTS diagnosis.ConclusionsPNTS to the BP can occur years after initial cancer diagnosis and may signify cancer progression. A high index of suspicion is crucial for timely diagnosis, particularly in patients with cancer and progressive upper extremity symptoms. Comprehensive imaging, including BP MRI and PET/CT, is essential for diagnosis. Despite treatment, prognosis remains poor, highlighting the need for improved diagnostic and therapeutic strategies.

Objective Perineural spread (PNS) of breast carcinoma to the brachial plexus is rare. This study investigates the radiologic features supporting the medial and lateral pectoral nerves (MPN and LPN, respectively) as pathways for PNS of breast cancer to the brachial plexus. Methods We reviewed 19 patients with biopsy-proven PNS of breast carcinoma to the brachial plexus. All available MRI and 18 F-FDG PET/CT studies were re-evaluated by a musculoskeletal radiologist with expertise in PNS. Imaging features of interest included pectoralis major and minor muscle MRI signal abnormality, abnormal FDG activity, and atrophy; FDG avidity within or along the course of the pectoral nerves; and extent of brachial plexus involvement on MRI and 18 F-FDG PET/CT. Demographic and clinical data were also collected. Results All 19 patients had MRI and 18 F-FDG PET/CT scans. Six patients showed clear radiologic evidence of PNS via the pectoral nerves. All six patients demonstrated abnormal MRI signal or enhancement in both the pectoralis major and minor muscles and increased FDG uptake was present in the pectoralis major in 4/6 patients and pectoralis minor in 5/6 patients. Five patients demonstrated atrophy of both the pectoralis major and minor muscles. Increased FDG uptake was noted along the LPN in five patients and the MPN in four. All exhibited brachial plexus enhancement on MRI and increased FDG uptake on PET/CT, supporting contiguous spread from the pectoral nerves. Conclusion This study provides radiologic support for the MPN and LPN as a potential pathway for PNS of breast cancer to the brachial plexus. Pectoralis major/minor muscle atrophy, abnormal MRI signal or enhancement, and increased FDG activity within the pectoral muscles and/or along the pectoral nerves may serve as early, non-invasive imaging markers of this process, with potential implications for diagnosis and management.

Abstract 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.

Schwannomatosis is characterized by the development of multiple schwannomas without evidence of vestibular tumors. Segmental schwannomatosis is defined as being limited to one limb or five or fewer contiguous segments of the spine. We report a case of a 20-year-old male with the painful masses of the left upper extremity with associated numbness and paresthesia in the ulnar nerve distribution. The high-frequency ultrasound showed that the ulnar nerve fascicles were enlarged and expanded with beadlike growth. The patient underwent surgery twice and all the tumors were pathologically confirmed to be schwannomas. Together, the medical history, imaging, and pathology findings indicated the diagnosis of segmental schwannomatosis. By the imaging diagnostic tools, MRI is the most commonly used in assistance with diagnosis of segmental schwannomatosis while high-frequency ultrasonography is rare. In this paper, we discuss the value of high-frequency ultrasonography in the diagnosis of this rare disease. This case report provides a deeper understanding of segmental schwannomatosis and may help improve the accuracy of preoperative diagnosis.

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.

Background Vagal schwannomas are well-documented, but cervical sympathetic chain schwannomas (CSCS) are rare, with most knowledge from case reports. This study aims to identify radiological predictors of misdiagnosis and factors guiding surgical approaches based on tumor size and extent. Methods An ambispective analysis was conducted on 21 cases of CSCS, examining preoperative data, intraoperative findings and the questionnaire to identify the potential predictors. Tumors were classified into three types based on their relationship with the carotid sheath, and this classification was correlated with vessel ligation and postoperative neural outcomes. Results An excellent agreement was found between radiologist on new classification system(Kappa:0.89). Tumor classification revealed a diverse distribution, with 6 cases identified as Type 1, 6 as Type 2, 5 as Type 3, and 4 as Type 3S. The necessity of external carotid artery (ECA) ligation correlated with the tumor type. Type 3 tumors required ECA ligation in 50% of cases, while Type 1 and Type 2 tumors predominantly involved vascular preservation. Postoperative complications included vagal palsy in 28.5% of cases and first bite syndrome in 71.4%. Conclusion Accurate preoperative planning and a novel staging system can enhance surgical outcomes and reduce postoperative complications as validated by our study.

AbstractObjectivesWe assessed whether quantitative imaging biomarkers derived from fluorodeoxyglucose-positron emission tomography (18F-FDG PET) could be extracted from perineural spread (PNS) in head and neck malignancies (HNM) to improve patient risk stratification.MethodsA case–control exploratory study (1:2 ratio) enrolled 81 patients with FDG-avid HNM. The case-group comprised 28 patients with documented PNS (reference: expert consensus), including 14 squamous cell carcinomas (SCC). Imaging biomarkers were extracted from the PNS on 18F-FDG PET, CT-scan, and MRI. The control-group enrolled 53 SCCs. The Cox proportional-hazards regression model explored the association with overall survival by univariate and multivariate analyses.ResultsThe rate of PNS detection by 18F-FDG PET was 100% in the case-group. Quantitative imaging biomarkers were not associated with the presence of sensory (p>0.20) or motor (p>0.10) symptoms. In SCC patients (case: 14; control: 53), PNS was associated with a hazard ratio of death of 5.5 (95%CI: 1.4:20.9) by multivariate analysis. Increased cranial nerve SUVmax was significantly associated with poorer overall survival by univariate analysis (p=0.001).ConclusionsOur pilot study showed the feasibility of extracting 18F-FDG PET biomarkers from PNS in FDG-avid HNM. Our results encourage the development of new PET/CT- or PET/MRI-guided management strategies in further prospective studies.Key Points• 18F-FDG PET/CT detects PNS in FDG-avid HNM.• PNS metabolism is more heterogeneous than healthy tissue.• PNS diagnosis is crucial: most patients were asymptomatic, N0 and M0.• PNS diagnosis is associated with poorer overall survival in SCC.• PET/CT- or PET/MRI-guided management strategies should be evaluated.

Abstract BACKGROUND AND IMPORTANCE Malignant peripheral nerve sheath tumors (MPNST) are relatively rare tumors of peripheral nerves that are notable for their locally aggressive nature, ability to metastasize, poor prognosis, and association with Neurofibromatosis type I. We present the case of a patient with a trigeminal nerve MPNST who developed an unusual metastasis to the corpus callosum, in the absence of any other central nervous system or systemic metastatic disease. We review the pathology and presentation of MPNST. CLINICAL PRESENTATION A 53-yr-old woman presented with a 1-yr history of paroxysmal facial pain and dysesthesias in the right V1 and V2 distributions of the trigeminal nerve. She was initially diagnosed with trigeminal neuralgia although further imaging showed a cavernous sinus mass extending along the trigeminal nerve. She later developed an isolated lesion in the corpus callosum that was biopsied and consistent with MPNST. CONCLUSION This case reviews the pathology and aggressive nature of MPNST and demonstrates an unusual site of metastasis. Clinicians should remain aware that MPNST can metastasize to sites in the central nervous system as well as systemically. Furthermore, clinicians should have a high index of suspicion for secondary causes of trigeminal neuralgia in cases with atypical features.