Hybrid Neurofibroma/Schwannoma is Overrepresented Among Schwannomatosis and Neurofibromatosis Patients

Cytological features of cranial and paraspinal nerve Tumours

The 2021 World Health Organization Classification of Central Nervous System Tumours introduced significant revisions to the categorization of paraspinal and nerve sheath tumours. This updated system encompasses seven tumour types: schwannoma, neurofibroma, perineurioma, hybrid nerve sheath tumours, malignant melanotic nerve sheath tumour, malignant peripheral nerve sheath tumour and cauda equina neuroendocrine tumour. This review provides an image-rich cytologic reference of these tumours, with particular emphasis on intraoperative smear preparations. Knowledge of the key cytological features of these tumours and their differential diagnoses will help guide classification of these challenging entities.

Schwannian and Perineuriomatous Differentiation in a Series of Giant Congenital Melanocytic Nevi

ABSTRACT

Close relationship between melanocytes and neural cells is accepted to reflect their common derivation from the neural crest and tumors combining both elements. We present a series of 10 patients with giant congenital melanocytic nevi (CMN) in which a secondary proliferation (11 lesions) with schwannian and/or perineuriomatous differentiation developed in the course of the disease. The age of the patients (4 male and 6 female) at the time of surgery and histological assessment varied from 3 months to 57 years. Histopathologically, the following subgroups were delineated: (1) nodular/tumoriform "neurotization" in CMN, (2) diffuse neurofibroma-like proliferation within CMN, (3) plexiform neurofibroma-like proliferation within CMN, and (4) diffuse perineuriomatous (hybrid schwannomatous-perineuriomatous) differentiation in CMN. We review the pertinent literature, including the role of recently identified Schwann cell precursors which are believed to represent the nerve-associated state of neural crest-like cells that persists into later developmental stages.

Hybrid peripheral nerve sheath tumours: MRI features with pathological correlation in 24 cases

OBJECTIVES

To describe the MRI features of histologically proven hybrid peripheral nerve sheath tumours (HPNST).

METHODS

A retrospective analysis of the MRI features of 24 histologically proven cases of HPNST over 7 years. Demographic data obtained from clinical records included age, gender, and date of diagnosis. Two readers independently assessed MRI studies and assessed the following features: involvement of a major nerve, intramuscular location, lesion morphology, entering nerve sign, exiting nerve sign, target sign, fascicular sign, split fat sign, and ancient change (cystic change). Inter-observer agreement was assessed with Cohen's kappa coefficient. Histological diagnosis was based on either image-guided needle biopsy or resection histology.

RESULTS

The study included 9 males and 15 females with mean age 50 years (range: 24-78 years). Nine tumours (35%) involved a major nerve including spinal roots (5), radial (1), median (1), tibial (1), and axillary (1), while 5 (21%) tumours were intramuscular. The mean tumour size was 4.2 cm (standard deviation of 2.4 cm). The frequency of MRI features was as follows: lobular contour (71%; 17/24), ancient change (38%; 9/24), fascicular sign (17%; 4/24), entering nerve sign (21%; 5/24), exiting nerve sign (13%; 3/24), target sign (13%; 3/24), and split fat sign (8%; 2/24). Inter-observer agreement was high, ranging from 0.7 to 0.83.

CONCLUSIONS

HPNST infrequently demonstrate the classical MRI signs of benign peripheral nerve sheath tumours, but commonly have a lobular morphology and can show ancient/cystic change.

ADVANCES IN KNOWLEDGE

This is the first study in the literature analysing the MRI features of histologically proven HPNST. HPNST infrequently shows the classical MRI signs that would be expected with benign peripheral nerve sheath tumours although commonly have a lobular morphology and show cystic change.

Peripheral nerve tumors

The chapter is focused on the neoplastic peripheral nerve lesions, which primarily involve "cranial and paraspinal nerves," as outlined in the CNS volume (WHO_Classification_of_Tumours_Editorial_Board, 2021). These include classic peripheral nerve sheath tumors such as schwannoma, neurofibroma, intraneural perineurioma, and malignant peripheral nerve sheath tumors, with their variants as well as new and more precisely defined entities, including hybrid nerve sheath tumors and malignant melanotic nerve sheath tumor (previously melanotic schwannoma).

Schwannomatosis: a Realm Reborn: year one

PURPOSE OF REVIEW

In 2022, an international consensus recommendation revised the nomenclature for neurofibromatosis type 2 ( NF2 ) and Schwannomatosis (SWN), now grouped under the umbrella term Schwannomatosis, and defined new diagnostic criteria.

RECENT FINDINGS

This review describes the molecular criteria for diagnosis of schwannomatosis and the subsequent diagnosis strategy, while setting out the most recent advances in our understanding of the natural history, pathology, molecular biology and treatment of schwannomatosis-associated tumors, including schwannomas, meningiomas and ependymomas.

SUMMARY

Somatic mutation screening should become a new standard for the diagnosis of NF2 -, LTZTR1 -, SMARCB1 - and 22q-schwannomatosis to discriminate those conditions. Constitutional events in NF2 -Schwannomatosis have a major influence on disease severity and justifiably motivate ongoing efforts on gene replacement therapy research. On the other hand, underlying mechanisms of disease severity and associated pain remain largely unknown in non- NF2 -SWN and independent of germline mutation. Research efforts therefore focus on pain relief in ongoing trials and the discovery of new molecular mechanisms underlying schwannoma tumorigenesis/pain/neuropathies.

Hybrid Schwannoma/Neurofibroma of the Neck: A Case Report

Neck hybrid schwannoma/neurofibromas are uncommon and classified as peripheral nerve sheath tumors (PNSTs). PNSTs develop from soft tissues, of which schwannoma, perineurioma, and neurofibroma are the most common. Hybrid PNSTs consist of more than 1 type of PNST, such as hybrid schwannoma/neurofibromas. The exact epidemiology and pathogenesis of these tumors are still largely unknown because of the limited studies on this topic. Such tumors can spread over the soft tissues, although most cases reported involve the subcutaneous layer or dermis. Some studies have suggested that hybrid schwannoma/neurofibromas may be associated with neurofibromatosis. We present a case of a 51-year-old female patient with a neck hybrid schwannoma/neurofibroma diagnosed by histopathology and immunohistochemistry. The patient was referred to the neurology department for neurofibromatosis screening, which reported negative results. After 12 months, the patient showed no evidence of tumor recurrence.

Intradural Extramedullary Tumors and Associated Syndromes

Most intradural tumors are located within the intradural extramedullary compartment, and the most common tumors are schwannomas and meningiomas. Other less common neoplasms include neurofibroma, solitary fibrous tumor, myxopapillary ependymoma, lymphoma, metastatic leptomeningeal disease, malignant peripheral nerve sheath tumor, and paraganglioma. Patients usually present with gait ataxia, radicular pain, and motor and sensory deficits due to chronic compressive myelopathy or radiculopathy. MRI is the modality of choice for detecting and evaluating intradural extramedullary spinal tumors. This imaging technique helps narrow the differential diagnosis and therefore decide treatment.

Hybrid Neurofibroma/Schwannoma of the Oral Cavity: A Rare Case Report and Literature Review

Hybrid peripheral nerve sheath tumors show combined features of more than one type of conventional benign peripheral nerve sheath tumors. There are few cases reported of hybrid peripheral nerve sheath tumors in the head and neck region. A 68-year-old female patient was referred for evaluation of an oral swelling lasting five years. Intraoral examination revealed a small mobile nodule located in the lower vestibule. The patient underwent excisional biopsy and microscopic evaluation showed typical features of neurofibroma enclosing areas with palisading nuclei compatible with Antoni A pattern, which are seen in schwannomas. These regions showed strong and diffuse immunoreactivity for S100 protein and moderate positivity in the neurofibroma area. CD34 was positive in the neurofibroma area and entrapped axons were positive for neurofilament. The final diagnosis was oral hybrid neurofibroma-schwannoma tumor. Hybrid peripheral nerve sheath tumors, although extremely rare, may arise within the oral cavity. To the best of our knowledge, this is the first neurofibroma-schwannoma tumor reported in the oral cavity. Recognizing hybrid peripheral nerve sheath tumors as a distinct clinicopathological entity is important because they may also be associated with syndromic disorders.

[Histological and molecular characteristics of tumours of the peripheral nervous system]

Tumours of the peripheral nervous system occur sporadically in adults and except for a minority of entities, these tumours are usually benign. The most common are nerve sheath tumours. Because these tumours grow in direct proximity or even invade peripheral nerve bundles, they can lead to severe pain and motion deficits. From the neurosurgical perspective these tumours are technically challenging, and especially for tumours with an invasive growth pattern complete resection may not be possible. Peripheral nervous system tumours that are associated with tumour syndromes such as neurofibromatosis type 1 and 2 or schwannomatosis are a particular clinical challenge. The goal of the current article is to present histological and molecular characteristics of peripheral nervous system tumours. Furthermore, future targeted therapy strategies are presented.

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.

Diagnosis and Treatment of Peripheral and Cranial Nerve Tumors with Expert Recommendations: An EUropean Network for RAre CANcers (EURACAN) Initiative

The 2021 WHO classification of the CNS Tumors identifies as "Peripheral nerve sheath tumors" (PNST) some entities with specific clinical and anatomical characteristics, histological and molecular markers, imaging findings, and aggressiveness. The Task Force has reviewed the evidence of diagnostic and therapeutic interventions, which is particularly low due to the rarity, and drawn recommendations accordingly. Tumor diagnosis is primarily based on hematoxylin and eosin-stained sections and immunohistochemistry. Molecular analysis is not essential to establish the histological nature of these tumors, although genetic analyses on DNA extracted from PNST (neurofibromas/schwannomas) is required to diagnose mosaic forms of NF1 and SPS. MRI is the gold-standard to delineate the extension with respect to adjacent structures. Gross-total resection is the first choice, and can be curative in benign lesions; however, the extent of resection must be balanced with preservation of nerve functioning. Radiotherapy can be omitted in benign tumors after complete resection and in NF-related tumors, due to the theoretic risk of secondary malignancies in a tumor-suppressor syndrome. Systemic therapy should be considered in incomplete resected plexiform neurofibromas/MPNSTs. MEK inhibitor selumetinib can be used in NF1 children ≥2 years with inoperable/symptomatic plexiform neurofibromas, while anthracycline-based treatment is the first choice for unresectable/locally advanced/metastatic MPNST. Clinical trials on other MEK1-2 inhibitors alone or in combination with mTOR inhibitors are under investigation in plexiform neurofibromas and MPNST, respectively.

Understanding barriers to diagnosis in a rare, genetic disease: Delays and errors in diagnosing schwannomatosis

Diagnosis of rare, genetic diseases is challenging, but conceptual frameworks of the diagnostic process can guide quality improvement initiatives. Using the National Academy of Medicine diagnostic framework, we assessed the extent of, and reasons for diagnostic delays and diagnostic errors in schwannomatosis, a neurogenetic syndrome characterized by nerve sheath tumors and chronic pain. We reviewed the medical records of 97 people with confirmed or probable schwannomatosis seen in two US tertiary care clinics. Time-to-event analysis revealed a median time from first symptom to diagnosis of 16.7 years (95% CI, 7.5-26.0 years) and median time from first medical consultation to diagnosis of 9.8 years (95% CI, 3.5-16.2 years). Factors associated with longer times to diagnosis included initial signs/symptoms that were intermittent, non-specific, or occurred at younger ages (p < 0.05). Thirty-six percent of patients were misdiagnosed; misdiagnoses were of underlying genetic condition (18.6%), pain etiology (16.5%), and nerve sheath tumor presence/pathology (11.3%) (non-mutually exclusive categories). One-fifth (19.6%) of patients had a clear missed opportunity for genetics workup that could have led to an earlier schwannomatosis diagnosis. These results suggest that interventions in clinician education, genetic testing availability, expert review of pathology findings, and automatic triggers for genetics referrals may improve diagnosis of schwannomatosis.

Practical Approach to Histological Diagnosis of Peripheral Nerve Sheath Tumors: An Update

Peripheral nerve sheath tumors encompass a wide spectrum of lesions with different biological behavior, including both benign and malignant neoplasms as well as the recent diagnostic category, i.e., “atypical neurofibromatous neoplasm with uncertain biologic potential” to be used only for NF1 patients. Neurofibromas and schwannomas are benign Schwann-cell-derived peripheral nerve sheath tumors arising as isolated lesions or within the context of classical neurofibromatosis or schwannomatoses. Multiple tumors are a hallmark of neurofibromatosis type 1(NF1) and related forms, NF2-related-schwannomatosis (formerly NF2) or SMARCB1/LZTR1-related schwannomatoses. Perineuriomas are benign, mostly sporadic, peripheral nerve sheath tumors that show morphological, immunohistochemical, and ultrastructural features reminiscent of perineurial differentiation. Hybrid tumors exist, with the most common lesions represented by a variable mixture of neurofibromas, schwannomas, and perineuriomas. Conversely, malignant peripheral nerve sheath tumors are soft tissue sarcomas that may arise from a peripheral nerve or a pre-existing neurofibroma, and in about 50% of cases, these tumors are associated with NF1. The present review emphasizes the main clinicopathologic features of each pathological entity, focusing on the diagnostic clues and unusual morphological variants.

Hybrid neurofibroma/schwannoma of the orbit

Hybrid neurofibroma/schwannoma is a rare variant of hybrid peripheral nerve sheath tumours (HPNST). A Medline search up to December 2021 identified only six cases of this tumour in the orbit. We report the case of a 78-year-old man who presented with left exophthalmos. Computed tomography showed a left intraconal orbital mass. The clinico-radiological diagnosis was consistent with an intraconal cavernous angioma. Orbitotomy was performed, obtaining an 18×16×11mm mass. Two different morphologies were seen microscopically, diagnostic of hybrid neurofibroma/schwannoma. HPNSTs of the orbit are uncommon and most reported cases showed a hybrid neurofibroma/schwannoma morphology. Hybrid neurofibroma/schwannomas have been associated with neurofibromatosis and schwannomatosis. Local recurrences have been reported. The correct identification of these tumours is important due to their potential use as a syndromic marker.

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.

Clinicopathologic and Molecular Study of Hybrid Nerve Sheath Tumors Reveals Their Common Association With Fusions Involving VGLL3

A subset of benign peripheral nerve sheath tumors are "hybrid" combining several lines of differentiation, most often schwannian and perineurial features. The pathogenesis of these tumors was poorly described until the recent discovery of recurrent VGLL3 rearrangements in hybrid schwannoma/perineuriomas, supporting the hypothesis that this entity represents a distinct subgroup of tumors and not only a morphologic variation of other peripheral nerve sheath tumors. Following this finding, we investigated 10 cases of hybrid peripheral nerve sheath tumors with immunohistochemistry, RNA sequencing, and array comparative genomic hybridization. By light microscopy, 7 tumors were hybrid schwannoma/perineurioma tumors, and 3 were hybrid schwannoma/neurofibroma. Most cases of hybrid schwannoma/perineuriomas displayed VGLL3 rearrangements fused in 5' either to CHD7 or CHD9 (n=6/7) and had simple diploid genetic profiles with few copy number alterations. Compared with a control group composed of 28 tumors associated with varied neural phenotypes, all VGLL3-fused tumors clustered together by transcriptomic analysis. In contrast, 1 case of hybrid schwannoma/perineurioma tumor harbored a CDH9-ZFHX3 fusion, a prominent perineurial component identified by immunohistochemistry and clustered with perineuriomas. No recurrent genetic alteration was seen in the 3 hybrid schwannoma/neurofibromas. To summarize, this study confirms and expands the recent findings on hybrid schwannoma/perineurioma, highlighting the predominance of VGLL3 fusions in these tumors.

Hybrid peripheral nerve sheath tumor of parapharyngeal space having features of neurofibroma and schwannoma in an 8-year-old child - A rare entity

Tumors of the parapharyngeal space (PPS) are extremely rare inpediatric age group. Out of all head-and-neck neoplasms, PPS tumors comprise only 0.5%. Majority of neoplasms in poststyloid PPS are neurogenic tumors. Conventional benign peripheral nerve sheath tumor (PNST) includes neurofibromas, schwannomas and perineuriomas. Hybrid PNSTs are rare entities having combined features of more than one histologic type, and the World Health Organization Classification of Tumors of the Central Nervous System, in the latest 2016, 4^th edition, has recently recognized and published it. The most common hybrid tumor is schwannoma/perineuroma followed by neurofibroma/schwannoma and neurofibroma/perineuroma. Here, we are reporting a hybrid PNST which was completely excised and having combined features of neurofibroma and schwannoma, confirmed by both histopathologically and immunohistochemically, in an 8-year-old child, in PPS.

A Case of Multiple Perineuriomas in the Colon With Underlying Neurofibromatosis Type I

A 45-year-old woman was referred to us after a positive fecal occult blood test. Colonoscopy revealed a 20-mm polyp in the transverse colon and a 10-mm polyp in the sigmoid colon. Endoscopic mucosal resection was performed as a diagnostic treatment. Both resected polyps were histologically diagnosed as perineuriomas. She was later found to exhibit multiple café-au-lait spots on the skin and subsequently diagnosed as having neurofibromatosis type I (NF-1). Perineuriomas are rare benign peripheral nerve sheath tumors, with no reports of multiple colonic lesions in a patient with NF-1 to date. NF-1 might be associated with the onset of multiple perineuriomas.

Mesenchymal Tumors of the Mediastinum: An Update on Diagnostic Approach

Mesenchymal tumors of the mediastinum are a heterogenous group of rare tumors with divergent lineages. Mediastinal mesenchymal tumors are diagnostically challenging due to their diversity and morphologic overlap with nonmesenchymal lesions arising in the mediastinum. Accurate histologic diagnosis is critical for appropriate patient management and prognostication. Many mediastinal mesenchymal tumors affect distinct age groups or occur at specific mediastinal compartments. Neurogenic tumors, liposarcoma, solitary fibrous tumor, and synovial sarcoma are common mesenchymal tumors in the mediastinum. Herein, we provide an update on the diagnostic approach to mediastinal mesenchymal tumors and a review of the histologic features and differential diagnosis of common benign and malignant mesenchymal tumors of the mediastinum.

A Rare Perineurioma/Granular Cell Tumor Hybrid Peripheral Nerve Sheath Tumor

Hybrid peripheral nerve sheath tumors (PNSTs) are rare benign composite neoplasms demonstrating features of multiple endogenous nerve sheath cell types. Hybrid PNSTs with granular cell components are exceedingly rare. Only a handful number of hybrid PNSTs composed of granular cell tumor and perineurioma have been described to date. We present a rare hybrid of perineurioma and granular cell tumor and review the literature.

Hybrid Schwannoma/Perineurioma: Morphologic Variations and Genetic Profiles

To clarify the morphologic spectrum and molecular profiles of hybrid schwannoma/perineurioma (HSP), we investigated 15 tumors clinicopathologically and cytogenetically. HSP was classified into 2 morphologic types: mixed cellular and combined tumor types. The former comprising of 14 tumors mostly arose in the subcutaneous tissue of the extremities and the trunk of middle-aged adults. They were well-circumscribed and composed of elongated spindle-shaped tumor cells arranged in storiform and whorl patterns. Immunostaining revealed a mixed cellular proliferation of S-100 protein-positive and SOX10-positive Schwann cells and epithelial membrane antigen-positive, claudin 1-positive, and GLUT1-positive perineurial cells. During follow-up, no tumors were found to have recurred in any cases. In contrast, in the combined tumor type arising in the mediastinum of a young male with neurofibromatosis type 2, the intraneural perineurioma-like areas, characterized by small whorl-like structures, were present in plexiform schwannoma-like areas. No recurrence was noted in the case. Molecular analyses (array comparative genomic hybridization and fluorescence in situ hybridization) revealed LOH 22q in 2 tumors of 5 studied: one each of the mixed cellular and combined tumor types. Although the same diagnostic term, HSP, has been applied to both mixed and combined types, they should be separated from each other.

Hybrid schwannoma-perineurioma frequently harbors VGLL3 rearrangement

Benign peripheral nerve tumors include schwannoma, neurofibroma, and perineurioma, as well as a recently recognized group of tumors with dual patterns of differentiation. The molecular pathogenesis of these so-called "hybrid" tumors remains poorly understood. Following identification of a novel CHD7-VGLL3 fusion gene in a hybrid schwannoma-perineurioma, we evaluated an expanded cohort of this tumor-type-as well as tumors with VGLL3 rearrangement identified from a curated molecular database-to characterize the prevalence of fusion genes among these tumors. Eighteen tumors met the inclusion criteria for this study. RNA sequencing identified VGLL3 rearrangement in 14 of these cases; the partner genes included CHD7 (ten cases), CHD9 (two cases), and MAMLD1 (two cases). Two cases possessed altogether unrelated fusions, including: DST-BRAF and SQSTM1-CDX1 fusion genes. Finally, two cases lacked identifiable fusion products. These findings highlight the molecular diversity of these neoplasms, with frequent rearrangement of VGLL3. More importantly, despite their dual pattern of differentiation, our results reveal the pathogenesis of hybrid schwannoma-perineurioma is unrelated to conventional schwannoma and perineurioma, thereby implying this tumor represents an altogether pathologically distinct entity.

Diagnostic Pathology of Tumors of Peripheral Nerve

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.

COX2 expression is associated with preoperative tumor volume but not with volumetric tumor growth in vestibular schwannoma

OBJECTIVE

Vestibular schwannomas (VS) are benign slow growing tumors arising from the vestibular nerve. The role of cyclooxygenase 2 (COX2) in tumor development of growth has been addressed in a few studies with contradictory results and suggestions. We recently analyzed the immunohistochemical expression of COX2 in 1044 VS samples and described an association of higher COX2 expression with proliferation but found no influence by regular intake of acetylsalicylic acid. We now collected volumetric radiographic data of the preoperative tumor volume and growth to further test the role of COX2 in VS growth.

METHODS

Preoperative images of 898 primary sporadic vestibular schwannomas were assessed, and sufficient preoperative imaging was used for the volumetric measurement preoperative tumor volume (n = 747) and preoperative relative tumor growth (n = 171). Clinical parameters and results of the immunohistochemical expression of COX2 and MIB1 in resected tumor tissue samples were obtained from our prior study. ANOVA, CART-analysis and multivariate nominal logistic regression were used for statistical analysis.

RESULTS

Larger preoperative tumor volumes were observed with tumors of younger patients (p = 0.0288) and with higher COX2 expression scores (p < 0.0001). Higher MIB1 expression was associated with smaller tumors (p = 0.0149) but with increased radiographic tumor growth (p = 0.0003). Patients of older age had tumors with slower growth rates (p = 0.0311). In the multivariate analysis only MIB1 expression was an independent significant factor regarding tumor growth (p = 0.0002).

CONCLUSIONS

Higher expression of COX2 in schwannoma is associated with an increased preoperative tumor volume but not with radiographic tumor growth over time.

Targetable ERBB2 mutations identified in neurofibroma/schwannoma hybrid nerve sheath tumors

BACKGROUNDNeurofibroma/schwannoma hybrid nerve sheath tumors (N/S HNSTs) are neoplasms associated with larger nerves that occur sporadically and in the context of schwannomatosis or neurofibromatosis type 2 or 1. Clinical management of N/S HNSTs is challenging, especially for large tumors, and established systemic treatments are lacking.METHODSWe used next-generation sequencing and array-based DNA methylation profiling to determine the clinically actionable genomic and epigenomic landscapes of N/S HNSTs.RESULTSWhole-exome sequencing within a precision oncology program identified an activating mutation (p.Asp769Tyr) in the catalytic domain of the ERBB2 receptor tyrosine kinase in a patient with schwannomatosis-associated N/S HNST, and targeted treatment with the small-molecule ERBB inhibitor lapatinib led to prolonged clinical benefit and a lasting radiographic and metabolic response. Analysis of a multicenter validation cohort revealed recurrent ERBB2 mutations (p.Leu755Ser, p.Asp769Tyr, p.Val777Leu) in N/S HNSTs occurring in patients who met diagnostic criteria for sporadic schwannomatosis (3 of 7 patients), but not in N/S HNSTs arising in the context of neurofibromatosis (6 patients) or outside a tumor syndrome (1 patient), and showed that ERBB2-mutant N/S HNSTs cluster in a distinct subgroup of peripheral nerve sheath tumors based on genome-wide DNA methylation patterns.CONCLUSIONThese findings uncover a key biological feature of N/S HNSTs that may have important diagnostic and therapeutic implications.FUNDINGThis work was supported by grant H021 from DKFZ-HIPO, the University Cancer Center Frankfurt, and the Frankfurt Research Funding Clinician Scientist Program.

Orbital hybrid peripheral nerve sheath tumors

Hybrid peripheral nerve sheath tumors (HPNST) are recently classified tumors from the World Health Organization Classification of soft tissue tumors that display combined features of more than one peripheral nerve sheath tumor. Acknowledgment is important because of its association with the development of neurofibromatosis type 1, type 2, and schwannomatosis. Orbital involvement is rare and only six cases of HPNST have been documented on literature. This article serves to review the pathophysiology, clinical manifestation, diagnosis, treatment, and prognosis of this infrequent but important orbital tumor.

Revisiting the WHO classification system of soft tissue tumours: emphasis on advanced magnetic resonance imaging sequences. Part 1

The World Health Organisation (WHO) classification categorises musculoskeletal soft tissue tumours (STT) based on their similarity to normal adult tissue. The most recent WHO classification provides an updated scheme that integrates biological behaviour as a distinguishing feature in each subcategory; STTs are further subdivided as benign, intermediate (locally aggressive or rarely metastasising), and malignant. Although malignant STTs are infrequent in routine orthopaedic radiology practice, musculoskeletal radiologists must be familiar with the imaging appearance of malignant STTs and distinguish them from their benign counterparts for appropriate management. Magnetic resonance imaging (MRI) is the ideal modality for the detection, characterisation, and local staging of STT. This review will discuss the most recent updates to the WHO classification of STT that are relevant to radiologists in a routine clinical practice with MRI correlation. The utility of advanced MRI sequences such as diffusion weighted imaging, dynamic contrast enhanced sequences, and magnetic resonance spectroscopy to provide insight into the biological behaviour of various STTs is highlighted.

Supraclavicular Solitary Hybrid Schwannoma/Neurofibroma: A Case Report

Peripheral nerve sheath tumors (PNSTs) are benign lesions arising from the connective tissue sheath surrounding the neurons and are labeled schwannoma, perineurioma, or neurofibroma according to their histopathological characteristics. Lesions with a mixture of two or more of the aforementioned tumors are known as hybrid peripheral nerve sheath tumors (HPNSTs). These hybrid tumors have been described as rare entities. In this report, we present a case of a solitary hybrid schwannoma/neurofibroma in an unusual location.

Plexiform Schwannoma of the Oral Cavity: Report of Eight Cases and a Review of the Literature

Plexiform schwannoma represents an unusual schwannoma variant, characterized by multinodular growth grossly and/or microscopically. A review of the English-language literature reveals only 28 previously reported cases involving the oral cavity, and herein we present 8 additional cases. Among these 36 patients, the average age at diagnosis was 28 years (range 5 to 62 years), with a female-to-male ratio of 1.4:1. The most frequently involved sites were the tongue (n = 13) and lip (n = 11). Lesion duration prior to presentation averaged 5.3 years (range, 6 weeks to 26 years). The average lesion size was 2.1 cm (range, 0.3 to 16 cm). The typical clinical presentation was a painless mass, although infrequent findings included pain/discomfort, paresthesia, difficulty chewing, and limited buccal mobility. All cases clinically appeared as a solitary mass or localized cluster of tumor nodules, with the exception of one patient who had neurofibromatosis 2 (NF2) and exhibited two distinct nodules on the tongue and buccal mucosa. In addition, extraoral neural neoplasms were evident in four patients, including three with NF2. Typical microscopic findings included multiple well-circumscribed tumor nodules, each surrounded by a perineurium-derived capsule with immunoreactivity for epithelial membrane antigen. The nodules contained characteristically bland and diffusely S-100-positive spindle cells arranged in Antoni A and B patterns; however, modest nuclear pleomorphism was evident in three cases. Most patients (n = 23) were treated by excision or enucleation and curettage, and three patients experienced recurrence. Unlike plexiform neurofibromas, plexiform schwannomas exhibit only a weak association with neurofibromatosis and have no known malignant potential.

An update on the CNS manifestations of neurofibromatosis type 2

Neurofibromatosis type II (NF2) is a tumor predisposition syndrome characterized by the development of distinctive nervous system lesions. NF2 results from loss-of-function alterations in the NF2 gene on chromosome 22, with resultant dysfunction of its protein product merlin. NF2 is most commonly associated with the development of bilateral vestibular schwannomas; however, patients also have a predisposition to development of other tumors including meningiomas, ependymomas, and peripheral, spinal, and cranial nerve schwannomas. Patients may also develop other characteristic manifestations such as ocular lesions, neuropathies, meningioangiomatosis, and glial hamartia. NF2 has a highly variable clinical course, with some patients exhibiting a severe phenotype and development of multiple tumors at an early age, while others may be nearly asymptomatic throughout their lifetime. Despite the high morbidity associated with NF2 in severe cases, management of NF2-associated lesions primarily consists of surgical resection and treatment of symptoms, and there are currently no FDA-approved systemic therapies that address the underlying biology of the syndrome. Refinements to the diagnostic criteria of NF2 have been proposed over time due to increasing understanding of clinical and molecular data. Large-population studies have demonstrated that some features such as the development of gliomas and neurofibromas, currently included as diagnostic criteria, may require further clarification and modification. Meanwhile, burgeoning insights into the molecular biology of NF2 have shed light on the etiology and highly variable severity of the disease and suggested numerous putative molecular targets for therapeutic intervention. Here, we review the clinicopathologic features of NF2, current understanding of the molecular biology of NF2, particularly with regard to central nervous system lesions, ongoing therapeutic studies, and avenues for further research.

Surgical management of peripheral nerve sheath tumours in children, with special consideration of neurofibromatoses

INTRODUCTION

Peripheral nerve sheath tumours in children are a rare and heterogeneous group, consisting mostly of benign tumours as well as malignant neoplasms. Especially in the paediatric population, diagnostics and indication for therapy pose relevant challenges for neurosurgeons and paediatric neurologists alike. Most paediatric cases that need surgical intervention are associated to neurofibromatosis type 1 (NF1).

METHODS

We retrospectively reviewed all paediatric cases treated at the Department of Neurosurgery in Tübingen between 2006 and 2017 for peripheral nerve sheath tumours. We analysed clinical signs, symptoms, histology, association to an underlying phacomatosis and sensory/motor function.

RESULTS

Of the 82 identified patients, the majority had NF1 (76.8%). Nine children bore a sporadic tumour without underlying phacomatosis (11%), 8 had NF2 (9.8%) and 2 schwannomatosis (2.4%), A total of 168 surgical interventions were performed, and 206 tumours were removed. Indication for surgery was in most instances significant tumour growth (45.2%) followed by pain (33.9%). New deficits led to surgery in 12.5% of interventions; malignancy was suspected in 8.3%. Histopathology revealed mostly neurofibromas (82.5%), divided into cutaneous neurofibromas (10.7%), infiltrating plexiform neurofibromas (25.7%) and peripheral nerve-born neurofibromas (46.1%). 12.1% of tumours were schwannomas, 2.9% MPNST, 1.5% ganglioneuroma (n = 3) and 1 hybrid-neurofibroma and perineurinoma each. Leading symptoms, such as pain and motor and sensory deficits, improved after 125/166 interventions (74.4%), remained unchanged following 39 interventions (23.2%) and worsened in 4 occasions (2.4%).

CONCLUSION

Surgery is safe and effective for (neurofibromatosis associated) peripheral nerve sheath tumours in the paediatric population; however, management needs a multidisciplinary setting. We propose early surgical resection in paediatric patients with peripheral nerve sheath tumours with significant growth, or pain, or motor deficit, or suspected malignancy.

Peripheral nerve sheath tumors in Neurofibromatosis Type 2: Surgical and histopathologic features

OBJECTIVE

Management of peripheral nerve sheath tumors (PNST) in Neurofibromatosis Type 2 (NF2) is complicated by frequent involvement of major peripheral nerves and concern that these tumors may be plexiform and/or involve multiple fascicles. Hybrid histologic features of both schwannoma and neurofibroma have been described in NF2-associated tumors, although the incidence of this phenotype in PNSTs is unknown. We sought to define the outcomes of surgery for tumors involving major peripheral nerves in NF2 and identify the rate of hybrid histology in PNSTs.

PATIENTS AND METHODS

Functional outcomes of surgery for patients with tumors on major (named) peripheral nerves were recorded. Histopathologic analyses were performed on all available excised tumors.

RESULTS

Nineteen operations were performed in 12 patients with NF2, for resection of 28 PNSTs. Among 11 tumors involving major peripheral nerves, 10 involved nerves related to motor function. Presenting symptoms in this group included pain (9) and weakness (4). Median tumor diameter was 3.4 cm (range:2.2-10.3 cm). Gross-total resection was achieved in 10 cases. Motor function was stable/improved in 10 cases but diminished after one case involving a small motor fascicle. All tumors involved a single fascicle. Histopathologic analyses of 21 available specimens revealed 19 pure schwannomas. In two cases (10 %) hybrid features of both schwannoma and neurofibroma were identified, with mast cells within regions consistent with neurofibroma.

CONCLUSIONS

PNSTs can be resected safely in NF2, even if they involve major peripheral nerves. A small proportion (10 %) of these tumors harbor hybrid histologic features, which may explain reports of plexiform or multi-fascicular tumors in NF2.

Benign peripheral nerve tumors

Benign peripheral nerve tumors encompass a wide range of neoplasms and non-neoplastic tumor like lesions. Some of these lesions if not encountered in the setting of genetic syndromes, are occurring sporadically. The principles of oncology should be respectfully followed in every step of diagnostic approach and surgical management. Albeit, classified as benign, some of them do have different level of malignant potential, thus the treating physicians should be aware of that to avoid possible pitfalls with devastating outcomes. This article reviews the most common benign peripheral nerve tumors discussing the clinicopathological findings, imaging appearance and the current trend in their approach.

Multiple primary malignancies associated with a germline SMARCB1 pathogenic variant

A 51-year old presented with a 6-month history of increasing pelvic/lower back pain with nocturnal waking and episodes of anorexia and vomiting. Examination revealed right torticollis and Horner's syndrome, and a large abdominal mass arising from the pelvis. Magnetic resonance and positron emission tomography imaging revealed (A) a 14 cm heterogeneous enhancing mass, abutting the left kidney with standardised uptake value max = 2.9, (B) a large heterogeneous enhancing pelvic mass (C) mesenteric adenopathy standardised uptake value max = 10.3 and (D) 6 cm right lung apex mass standardised uptake value max = 4.3. Computerised tomography-guided biopsy of lesion A was reported as neurofibroma with occasional atypia, lesion B a benign uterine leiomyoma and lesion C follicular lymphoma world health organisation Grade 2. Although she had been given the diagnosis of Neurofibromatosis Type-1 (NF1) 25-years previously following removal of an intradural extramedullary schwannoma she had no cutaneous stigmata of NF1. Genetic analysis of blood lymphocyte DNA identified a pathogenic variant in SMARCB1 confirming a diagnosis of schwannomatosis. Following 6-months chemotherapy for lymphoma, surgery was performed to remove lesion A. Histology revealed a malignant peripheral nerve sheath tumour with areas of low and high-grade change. An incidental, well-differentiated small bowel neuroendocrine carcinoma was also excised. Close surveillance continues with no recurrence after 6 years. This case study describes a novel finding of three separate synchronous primary malignancies in a patient with schwannomatosis and a proven SMARCB1 pathogenic variant.

Nonepithelial Tumors and Tumor-like Lesions of the Skin and Subcutis in Children

This overview of mesenchymal tumors presenting in the skin and/or subcutis in children brings together the range of neoplasms and hamartomas which are seen in this age-group. It is not surprising from the perspective of the pediatric or general surgical pathologist that vascular anomalies, including true neoplasms and vascular malformations, are the common phenotypic category. Since there is considerable morphologic overlap among these lesions, clinicopathologic correlation may be more important than for many of the other mesenchymal tumors. The skin and subcutis are the most common sites of clinical presentation for the infantile myofibroma which is the most common of fibrous mesenchymal tumors in children. Several of the other mesenchymal tumors are more common adults-like dermatofibrosarcoma protuberans, but nonetheless have an important presence in children, even as a congenital neoplasm. A lipomatous tumor in a young child should be considered as a possible manifestation of an overgrowth syndrome.

[Pathogenesis and molecular pathology of vestibular schwannoma]

Schwannomas are benign Schwann cell-derived tumors of the peripheral nerve sheath often involving the vestibular cranial nerve (vestibular schwannoma). Histologically, they consist of bipolar spindle cells and show a moderate cellularity. Typically, Antoni A regions with a storiform pattern and loose Antoni B regions are intermingled. Verocay bodies are the pathognomonic palisading structures. Malignant transformation is rare. Merlin (schwannomin), the protein product of NF2, is inactivated by mutations, loss of heterozygosity or methylation. Within neurofibromatosis type 2, a germline mutation is present in about half of cases, whereas tumors demonstrate an additional second hit of the NF2 gene. A loss of chromosome 22 or 22q is common. Merlin links the cell membrane with the cytoskeleton and regulates intracellular signaling pathways leading to dysorganization when merlin is inactivated. Loss of merlin activates Rac1 and Ras, and the PAK1, mTORC1, EGFR-Ras-ERK, PI3K-Akt, WNT and Hippo pathways as well as receptor tyrosine kinases. Furthermore, merlin locates to the nucleus and inhibits E3 ubiquitin ligase CRL4^DCAF1. Besides biallelic inactivation of NF2 in schwannomas, other genes are involved in the pathogenesis of schwannomatosis-associated schwannomas such as LZTR1, SMARCB1, COQ6 indicating an important role of SWI/SNF chromatin-remodeling complex for schwannoma development. Our own investigations point to deregulation of BAF170, another essential SWI/SNF complex component. Knowledge of mechanisms allows targeted molecular therapy, especially in vestibular schwannomas, using antagonists against mTOR (rapamycin/sirolmus/everolimus), EGFR (lapatinib) or VEGF (bevacizumab), although clinical studies have been in part disappointing so far.

[Tumors of the inner ear and adjacent structures]

Tumors of the inner ear and adjacent structures often present with hearing loss, tinnitus and vertigo due to compression of the traversing cranial nerves. More than 90% of the tumors of the inner ear with or without expansion into the cerebellopontine angle are histologically diagnosed as vestibular schwannomas. Less common tumorous lesions include ectopic meningiomas located in the petrous bone, glomus tympanicum paragangliomas or endolymphatic sac tumors (ELST) originating in the vestibular recess. Most tumors are sporadic, but hereditary disorders have to be considered. Bilateral vestibular schwannomas are indicative of neurofibromatosis type 2 and ELST in conjunction with other abdominal tumors indicates von Hippel-Lindau disease. The neuropathological diagnostics and grading guides the subsequent therapy of these mostly benign lesions.

Soft Tissue Perineurioma in a Child With Neurofibromatosis Type 1: A Case Report and Review of the Literature

Soft tissue perineurioma is a rare benign peripheral nerve sheath tumor, especially in children. This manuscript presents an unusual case of soft tissue perineurioma in a 10-year-old boy with neurofibromatosis type 1. The patient presented with a lump in the region of the right breast. A subcutaneous, well circumscribed mass was removed. The cut surface was cream with a vaguely nodular appearance. Histology showed a spindle cell lesion with variable architecture and biphasic morphology. There was no nuclear atypia or pleomorphism. The differential diagnosis and other soft tissue lesions that can be seen in neurofibromatosis type 1 are discussed.

Neuropathies in the setting of Neurofibromatosis tumor syndromes: Complexities and opportunities

The term 'Neurofibromatosis' (NF) comprises a group of rare diseases with related clinical presentations but distinct genetic conditions. All currently known types - NF1, NF2 and Schwannomatosis - predispose afflicted individuals to the development of glial cell-derived (gliogenic) tumors. Furthermore, the occurrence of neuropathic symptoms, which add to the overall neurologic disability of patients, has been described in all disease entities. We show that neuropathic symptoms are a common and clinically important, yet infrequently studied feature in the NF spectrum. However, the clinical relevance and respective underlying pathogenesis, varies greatly among the different NF types. In this review, we summarize and interpret the latest basic research findings, as well as clinical observations, in respect of Neurofibromatosis-associated neuropathies.

Hybrid peripheral nerve sheath tumors: report of five cases and detailed review of literature

BACKGROUND

Hybrid peripheral nerve sheath tumors (PNSTs) have been recognized recently and were first included in the 4th edition of World Health Organization (WHO) Classification of Tumors of Soft tissue and Bone, published in 2013. These tumors show combined features of more than one type of conventional benign peripheral nerve sheath tumors. The most common combinations are those of schwannoma/perineurioma followed by combinations of neurofibroma/schwannoma and neurofibroma/perineurioma. A detailed literature review of published cases is presented. We have discussed the types and etiology, epidemiology and sites of localization, gross and microscopic appearances and immunohistochemical features of hybrid PNSTs and association of these tumors with tumor syndromes.

CASE PRESENTATION

We have included five cases which were diagnosed in our department as we believe that publication of these new cases is relevant for the improved understanding of these specific tumors. Four of our five patients were males, mean age was 24 years. There was wide variation in the location of these tumors. Mean size of excised tumors was 5.5 cms in the greatest dimensions. Three out of five cases represented hybrid schwannoma/perineurioma histologically. No significant nuclear atypia, mitotic activity or necrosis seen. All five cases were completely excised. All five patients are alive and well at the time of writing with no recurrence.

CONCLUSION

Hybrid PNSTs are distinct tumors and are usually benign. However, rare case reports have described local recurrence and at least two recent case reports have described malignant transformation in these tumors. Further studies on large number of cases are required to determine the exact pathogenetic basis of these tumors.

Diagnostic and Prognostic Relevance of the Cutaneous Manifestations of Neurofibromatosis Type 2

Neurofibromatosis type 2 is an autosomal dominant hereditary disease with complete penetrance. It gives rise to multiple central and peripheral nervous system tumors, ocular alterations, and various types of skin lesion. In general, neither dermatologists nor other specialists have in-depth knowledge of the clinical manifestations of neurofibromatosis type 2. In some cases, this can lead to delayed diagnosis, which can increase morbidity and mortality. We describe the less well known clinical manifestations of NF2, focusing particularly on skin lesions specific to this disease. Identification of these lesions, when present, can facilitate diagnosis.

Tumors displaying hybrid schwannoma and neurofibroma features in patients with neurofibromatosis type 2

Although schwannoma and neurofibroma tumors are generally reported as distinct pathologic diagnoses, sporadic schwannoma/neurofibroma hybrid nerve sheath tumors have been reported in the general population with components of both entities. We report the clinicopathological features of these hybrid nerve sheath tumors in patients with neurofibromatosis type 2 (NF2). A retrospective review of nerve sheath tumor surgical specimens from patients with NF2 enrolled at the National Institutes of Health was performed. Those specimens reported to have schwannoma-like and neurofibroma-like features were selected for further characterization by morphology, immunohistochemical panel (CD34, S100, neurofilament triplet protein (immunostain) (NFTP), epithelial membrane antigen (EMA)), and confirmation as hybrid tumors. Of 43 total NF2 patients undergoing resection of nerve sheath tumors, 11 specimens from 11 (26%) patients were found to be benign nerve sheath tumors exhibiting hybrid features of both neurofibroma and schwannoma. Immunohistochemical studies showed the schwannoma component to be S100+, CD 34- while the neurofibroma component was CD34+, variable S100+. Our experience emphasizes the importance of including this distinct tumor subtype, the schwannoma/neurofibroma hybrid tumor, in the differential diagnosis of nerve sheath tumors in NF2 patients and suggests that the relationship between neurofibroma and schwannoma tumors is closer than previously suspected.