Congenital and childhood plexiform (multinodular) cellular schwannoma: a troublesome mimic of malignant peripheral nerve sheath tumor

A 32-year-old man with plexiform schwannoma of the thyroid gland: a case report

Plexiform schwannomas representing a rare subset, comprise 5% of all schwannomas. However, their occurrence in the thyroid gland is exceptionally rare. A 32-year-old male presented with an incidentally discovered, asymptomatic thyroid mass. Imaging revealed an approximately 5 cm heterogeneous solid mass on the right thyroid lobe extending to the upper mediastinum and directly invading the upper trachea. Under the suspicion of thyroid malignancy, the patient underwent right thyroidectomy. Histological examination confirmed a plexiform schwannoma with S100-positive spindle cells. Currently, the patient is undergoing outpatient follow-up, with no reported complications. To our knowledge, this is the first documented case of plexiform schwannoma of the thyroid gland within the English literature. This case highlights the diverse and unpredictable clinical manifestations of thyroid masses, emphasizing the importance of a multidisciplinary approach for diagnosing and managing rare entities, such as thyroid gland schwannomas.

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).

Update of pediatric soft tissue tumors with review of conventional MRI appearance-part 2: vascular lesions, fibrohistiocytic tumors, muscle tumors, peripheral nerve sheath tumors, tumors of uncertain differentiation, and undifferentiated small round cell sarcomas

There are numerous soft tissue tumors and tumor-like conditions in the pediatric population. Magnetic resonance imaging is the most useful modality for imaging these lesions. Although certain soft tissue lesions exhibit magnetic resonance features characteristic of a specific diagnosis, most lesions are indeterminate, and a biopsy is necessary for diagnosis. We provide a detailed update of soft tissue tumors and tumor-like conditions that occur in the pediatric population, emphasizing each lesion's conventional magnetic resonance imaging appearance, using the recently released 5^th edition of the World Health Organization Classification of Soft Tissue and Bone Tumors as a guide. In part one of this review, pediatric tumor-like lesions, adipocytic tumors, fibroblastic and myofibroblastic tumors, and perivascular tumors are discussed. In part two, vascular lesions, fibrohistiocytic tumors, muscle tumors, peripheral nerve sheath tumors, tumors of uncertain differentiation, and undifferentiated small round cell sarcomas are reviewed. Per the convention of the WHO, these lesions involve the connective, subcutaneous, and other non-parenchymatous organ soft tissues, as well as the peripheral and autonomic nervous system.

Plexiform Cellular Schwannoma in Infancy and Childhood: A Clinicopathological Study of Seven Cases of an Underrecognized Nerve Sheath Tumor with a Tendency Toward Local Recurrence

Plexiform cellular schwannoma (PCS) is very rare, and it is not completely understood. We present our experience with 7 additional cases of PCS in infancy and childhood to further characterize its distinctive clinicopathological features. There were 5 females and 2 males with a mean age of 28 months (ranging, 2 months to 8 years). The involved sites included the left forearm (n = 2), sacrococcygeal region (n = 2), retroperitoneum (n = 1), thoracic spinal canal and thoracic cavity (n = 1), and neck (n = 1). Tumor sizes ranged from 3 to 13 cm in maximum diameter (mean, 7.1 cm). Histologically, all tumors consisted of abundant spindle cells arranged in a multinodular or plexiform growth pattern, possessing elongated, hyperchromatic nuclei and pale eosinophilic cytoplasm with indistinct cell margins. Mitotic figures were easily identified, with a mean count of 4 per 10 consecutive high power fields (HPF). Immunohistochemically, all tumors were strongly and diffusely positive for S100 protein, SOX10 and H3K27me3. The Ki-67 index ranged from 5% to 30% (mean, 15%). Follow-up (available in 6 cases) revealed that 5 patients experienced local recurrence and were treated by re-excision. There was no evidence of recurrence and metastasis in 3 patients, and the other 2 were alive with the disease. In conclusion, PCS is an uncommon nerve sheath tumor predominantly occurring in infants and children, featuring a plexiform or multinodular growth pattern and exhibiting a tendency toward local recurrence. PCS is easily mistaken as malignant peripheral nerve sheath tumor (MPNST) due to its locally aggressive behaviors and worrisome features, including hypercellularity, hyperchromatism and high proliferative activity. Increased awareness of its potential occurrence and greater familiarity with its characteristic features are helpful for both clinicians and pathologists to avoid misdiagnosis and unnecessary overtreatment.

Multinodular plexiform tumors of major peripheral nerves: A practical overview

BACKGROUND AND AIMS

Multinodular/plexiform schwannomas and neurofibromas of major nerves are rare: before surgery, differential diagnosis among these two uncommon variants is challenging. For both forms, surgical removal is recommended in case of progressive growth and worsening of neurological symptoms. Surgery has a higher risk of neurological damage than conventional schwannomas or neurofibromas. In literature, a comparison among these rare tumors is usually limited to the pathological aspect while specific surgical and clinical management indications are lacking. Cutaneous tumors of both forms arising from terminal peripheral nerves' branches might be treated by plastic surgeons while tumors of major nerves remain under neurosurgical competence. Here we report our recent neurosurgical experience on the matter, to furnish useful suggestions for the management of these tumors.

METHOD

We analyzed the clinical, radiological, and pathological data in a consecutive case series of plexiform/multinodular nerve tumors operated at our institution in the last five years.

RESULTS

In our series, neurofibroma type of plexiform tumors was more frequent than schwannoma type: two sporadic plexiform-multinodular schwannomas (patients 1, and 5) and three multinodular/plexiform Neurofibromatosis familial (Neurofibromatosis 1 / NF-1) (patients 2, 3, and 4). Surgery was complex when major nerves were involved. The early outcome appeared mostly related to the pre-surgical neurological conditions and histological grading.

INTERPRETATION

Although sharing some features, multinodular-plexiform schwannomas and neurofibromas have consistent differences from the clinical, surgical and pathological points of view.

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.

Cutaneous Spindle Cell Neoplasms: Pattern-Based Diagnostic Approach

Context.—

Spindle cell neoplasms arising in the skin comprise a heterogeneous group of tumors with divergent lineages. Cutaneous spindle cell neoplasms are relatively common and present surgical pathologists with diagnostic challenges. Recognition of their histopathologies is important for correct diagnosis and management. The current review presents a pattern-based diagnostic approach to common cutaneous spindle cell neoplasms that often cause diagnostic difficulties.

Objective.—

To provide a useful guide for diagnosis of cutaneous spindle cell neoplasms.

Data Sources.—

PubMed (US National Library of Medicine) reports and the authors' personal experiences are reviewed.

Conclusions.—

The authors briefly summarize the histologic features and differential diagnoses of common cutaneous spindle cell neoplasms.

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.

TFG-MET fusion in an infantile spindle cell sarcoma with neural features

An increasing number of congenital and infantile sarcomas displaying a primitive, monomorphic spindle cell phenotype have been characterized to harbor recurrent gene fusions, including infantile fibrosarcoma and congenital spindle cell rhabdomyosarcoma. Here, we report an unusual spindle cell sarcoma presenting as a large and infiltrative pelvic soft tissue mass in a 4-month-old girl, which revealed a novel TFG-MET gene fusion by whole transcriptome RNA sequencing. The tumor resembled the morphology of an infantile fibrosarcoma with both fascicular and patternless growth, however, it expressed strong S100 protein immunoreactivity, while lacking SOX10 staining and retaining H3K27me3 expression. Although this immunoprofile suggested partial neural/neuroectodermal differentiation, overall features were unusual and did not fit into any known tumor types (cellular schwannoma, MPNST), raising the possibility of a novel pathologic entity. The TFG-MET gene fusion expands the genetic spectrum implicated in the pathogenesis of congenital spindle cell sarcomas, with yet another example of kinase oncogenic activation through chromosomal translocation. The discovery of this new fusion is significant since the resulting MET activation can potentially be inhibited by targeted therapy, as MET inhibitors are presently available in clinical trials.

Pediatric Non-vestibular Schwannoma

While the clinicopathologic features of pediatric vestibular schwannomas, often in the context of neurofibromatosis type 2 (NF2), have been well studied, there is less data regarding the characteristics of pediatric non-vestibular schwannomas (NVS). Additionally, the rate of loss of SMARCB1/INI1 expression in this population has not been systematically evaluated. Our institutional archives were searched for cases of NVS arising in patients 18 years or younger. Clinicopathologic features including SMARCB1/INI1 status were assessed for each case. Twenty-three NVS from 9 males and 13 females (age range, 2 months to 18 years) were identified, and sites included paraspinal (n = 10), head and neck (n = 6), extremities (n = 4), trunk (n = 1), mediastinum (n = 1), and retroperitoneum (n = 1); 22 cases were Antoni A predominant with 6 cases comprising solely Antoni A tissue. The mitotic rate of the tumors ranged from 0 to 10/10 high-power fields (HPFs), and 3 tumors had mitotic rates of ≥4 mitoses/10 HPFs. Two tumors showed plexiform architecture. No NVS showed diffuse atypia, calcifications, microcystic/reticular architecture, epithelioid morphology, pseudoglandular change, neuroblastoma-like features, or necrosis. All tumors tested (23/23) showed retained nuclear expression of SMARCB1/INI1. Follow-up was available in 21 patients (range 1 week to 194 months), and 5 tumors recurred. Pediatric NVS have a relatively homogeneous appearance with a predominance of Antoni A areas. Pathologists should be aware that schwannomas in this age group may be cellular with mitotic rates of ≥4/10 HPFs to avoid misclassification as a spindle cell sarcoma.

Dermal and Subcutaneous Plexiform Soft Tissue Neoplasms

This article presents an overview of soft tissue tumors that have a plexiform histomorphology. The more commonly encountered entities, including plexiform fibrohistiocytic tumor, cellular neurothekeoma, dermal nerve sheath myxoma, plexiform schwannoma, and plexiform neurofibroma, are discussed in detail, and other tumors are noted. Information on clinical features, microscopic findings, ancillary studies, differential diagnosis, and prognosis is provided for each entity.

Cutaneous microcystic/reticular schwannoma: a poorly recognized entity

BACKGROUND

Microcystic/ reticular schwannoma is exceptionally rare yet distinctive morphological variant of schwannoma with predilection for visceral sites lacking association with neurofibromatosis.

AIMS

To further delineate clinicopathological features of cutaneous microcystic/reticular schwannoma and to discuss its differential diagnosis.

RESULTS

We analyzed three cutaneous microcystic/reticular schwannomas, occurring in two males and one female (mean age: 37.6 years). The tumors presented as a non-painful slightly raised papule (mean: 0.7 cm) on upper arm (n = 2) and back (n = 1). No recurrences were observed despite marginal excision (mean follow up: 42 months). Histopathologically, a multilobular proliferation was present in the dermis composed of bland tumor cells forming distinctive microcystic, reticular, lace-like or pseudoglandular structures, containing abundant myxoid/mucinous material. By immunohistochemistry, tumor cells lining microcystic structures corresponded to Schwann cells (diffuse S100 positive, variable GFAP positivity). A discontinuous EMA-positive perineurium was present at the periphery of some of the lobules.

CONCLUSION

Cutaneous microcystic/reticular schwannoma expands the spectrum of benign peripheral nerve sheath tumors with reticular morphology encountered in the skin. Other tumors in this group include reticular perineurioma and hybrid tumors with reticular morphology, e.g. reticular perineurioma/schwannoma and reticular perineurioma/neurofibroma.

Multiple plexiform schwannomas in the plantar aspect of the foot: case report and literature review

Background

Plexiform schwannoma (PS) is a rare, peripheral nerve sheath tumor arranged in a plexiform pattern.

Case presentation

We report an unusual case of a 19-year-old woman, who complained of pain in the plantar aspect of the left foot. Magnetic resonance image (MRI) demonstrates three solitary nodules of varying sizes in the deep soft tissue of the plantar aspect of the foot that are homogeneously isointense to skeletal muscle on T1-weighted images and hyperintense on T2-weighted fat-suppressed images, especially the rim of the lesion. Subsequent pathological examination confirmed the diagnosis of PS.

Conclusion

MRI characteristic plays an important role in detecting this rare lesion. A review of the literature on PS is also presented.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2474-15-342) contains supplementary material, which is available to authorized users.

Schwannomas and their pathogenesis

Schwannomas may occur spontaneously, or in the context of a familial tumor syndrome such as neurofibromatosis type 2 (NF2), schwannomatosis and Carney's complex. Schwannomas have a variety of morphological appearances, but they behave as World Health Organization (WHO) grade I tumors, and only very rarely undergo malignant transformation. Central to the pathogenesis of these tumors is loss of function of merlin, either by direct genetic change involving the NF2 gene on chromosome 22 or secondarily to merlin inactivation. The genetic pathways and morphological features of schwannomas associated with different genetic syndromes will be discussed. Merlin has multiple functions, including within the nucleus and at the cell membrane, and this review summarizes our current understanding of the mechanisms by which merlin loss is involved in schwannoma pathogenesis, highlighting potential areas for therapeutic intervention.

Intracerebral schwannomas: a rare disease with varying natural history

Although intracerebral schwannomas are typically regarded as benign intracranial tumors, malignancy and recurrence have been reported among patients harboring such neoplasms. The available literature consists of case reports and small series that present variable characteristics distinguishing these unusual lesions. Little advancement has been made to further the understanding and management of these tumors. The authors present 3 cases from their institution that highlight the difference between typical benign intracerebral schwannomas and histopathological variants that may portend more aggressive behavior. Also provided is a review of the literature in the hope of gaining a better understanding of these rare tumors.

Multinodular reticular schwannoma in the head and neck region: a potential diagnostic pitfall

Reticular/microcystic schwannoma is a recently described morphologic variant of schwannoma that occurs predominantly in visceral organs, most commonly the gastrointestinal tract. This report describes a case occurring in the masticator space, accompanied by focal erosion of the orbital floor, clinically and radiologically worrisome for malignancy. The 26-year-old man presented with facial swelling for 3 month. The tumor shows a multinodular appearance, with dense lymphoplasmacytic infiltrates in the fibrous septa. The tumor nodules are composed of plump spindle cells disposed in a reticular pattern. The diagnosis is confirmed by strong positive staining for S100 protein. The differential diagnoses of reticular schwannoma in the soft tissues of head and neck region are different from those in the gastrointestinal tract.

Neurogenic tumors of soft tissue

Neurogenic tumors are an uncommon yet important category of soft tissue tumors in children and adolescents because of their frequent association with various genetic syndromes. The heterogeneous cellular composition of the peripheral nerve and the wide metaplastic capacity of the neural crest and its derivatives generate a variety of neoplasms with neurogenic differentiation. This article reviews the clinicopathologic features and differential diagnosis of neurogenic tumors in the first two decades of life, and highlights use of selected ancillary methods for diagnosis.

Pathology of peripheral nerve sheath tumors: diagnostic overview and update on selected diagnostic problems

Peripheral nerve sheath tumors are common neoplasms, with classic identifiable features, but on occasion, they are diagnostically challenging. Although well-defined subtypes of peripheral nerve sheath tumors were described early in the history of surgical pathology, controversies regarding the classification and grading of these tumors persist. Advances in molecular biology have provided new insights into the nature of the various peripheral nerve sheath tumors, and have begun to suggest novel targeted therapeutic approaches. In this review, we discuss current concepts and problematic areas in the pathology of peripheral nerve sheath tumors. Diagnostic criteria and differential diagnosis for the major categories of nerve sheath tumors are proposed, including neurofibroma, schwannoma, and perineurioma. Diagnostically challenging variants, including plexiform, cellular and melanotic schwannomas are highlighted. A subset of these affects the childhood population, and has historically been interpreted as malignant, although current evidence and outcome data suggest they represent benign entities. The growing current literature and the author's experience with difficult to classify borderline or "hybrid tumors" are discussed and illustrated. Some of these classification gray zones occur with frequency in the gastrointestinal tract, an anatomical compartment that must always be entertained when examining these neoplasms. Other growing recent areas of interest include the heterogeneous group of pseudoneoplastic lesions involving peripheral nerve composed of mature adipose tissue and/or skeletal muscle, such as the enigmatic neuromuscular choristoma. Malignant peripheral nerve sheath tumors (MPNST) represent a diagnostically controversial group; difficulties in grading and guidelines to separate "atypical neurofibroma" from MPNST are provided. There is an increasing literature of MPNST mimics which neuropathologists must be aware of, including synovial sarcoma and ossifying fibromyxoid tumor. Finally, we discuss entities that are lacking from the section on cranial and paraspinal nerves in the current WHO classification, and that may warrant inclusion in future classifications. In summary, although the diagnosis and classification of most conventional peripheral nerve sheath tumors are relatively straightforward for the experienced observer, yet borderline and difficult-to-classify neoplasms continue to be problematic. In the current review, we attempt to provide some useful guidelines for the surgical neuropathologist to help navigate these persistent, challenging problems.

Trisomy 17 in congenital plexiform (multinodular) cellular schwannoma

Plexiform (multinodular) cellular schwannomas are rare tumors, not associated with neurofibromatosis type 1, that occur more often in children and can be congenital. Their biology is benign and is characterized by the tendency to recur locally without being metastatic. Cytogenetic studies in adult cases of schwannoma indicate a complete or partial loss of chromosome 22 as the most common abnormality. Only two cytogenetic studies describe cases in children, one of which concerned a congenital cellular plexiform schwannoma. Here, we report the cytogenetic analysis of a second case in an 8-month-old boy with recurrence of trisomy 17.

Plexiform schwannoma of the foot: a review of the literature and case report

Plexiform schwannoma is a rare variety of benign nerve sheath tumor that is usually confined to the head and neck or trunk. In this article, we describe the case of a plexiform schwannoma of the foot in an adult male. In addition to a review of the literature, we discuss diagnostic characteristics and differentiators for this tumor, an approach to surgical treatment, including reconstruction of the plantar foot defect after tumor extirpation, and why it is important for practicing foot and ankle surgeons to differentiate plexiform schwannoma from other similar tumors.

Multinodular/plexiform (multifascicular) schwannomas of major peripheral nerves: an underrecognized part of the spectrum of schwannomas

OBJECT

In clinical practice, schwannomas are among the most common types of nerve sheath tumors. Their clinical presentation, imaging characteristics, and operative features are well known. Over the past 20 years, clinical outcomes have improved due to resection of these tumors at a fascicular level. Despite these advances, a subgroup of patients with schwannomas is associated with a disappointing neurological outcome following resection. The purpose of this study was to correlate the imaging and histological features in this group of patients with more anatomically complex forms of schwannomas.

METHODS

In a retrospective review performed at their institution over a 10-year period, the authors found a subgroup of patients with complex multinodular/plexiform schwannomas affecting major peripheral nerves. Eleven patients were identified, and the clinical, imaging, and pathological features of their disease were reviewed.

RESULTS

The clinical presentation of multinodular/plexiform schwannomas of major peripheral nerves may be similar to that of conventional schwannomas, but their imaging features, operative appearance, and outcomes differ.

CONCLUSIONS

Preoperatively and intraoperatively, the distinguishing features of multinodular/plexiform schwannomas of major peripheral nerves may be subtle and can easily go unrecognized, thus explaining the often suboptimal surgical results. Familiarity with the imaging and operative features of multinodular/plexiform schwannomas will no doubt alter treatment approaches and improve neurological function in this subgroup of patients.

Plexiform malignant peripheral nerve sheath tumour of infancy and childhood of the index finger: Surgical treatment

We describe a rare case of plexiform malignant peripheral nerve sheath tumour (MPNST) of infancy and childhood in a 3.5-year-old girl. The tumour was located in the proximal phalanx of the left index finger. After initial excisions and a ray amputation, exarticulation of the third and fourth rays was required.

Plexiform schwannoma: a clinicopathologic overview with emphasis on the head and neck region

Plexiform schwannoma is a rare variant of Schwann cell tumor. Occurring in either conventional or cellular type, they are characterized either grossly or histologically by a plexiform pattern of intraneural growth often with multinodularity. Ordinary as well as plexiform schwannoma typically arise in superficial soft tissues and show a predilection for the head and neck region. Infrequent examples arise in the setting of neurofibromatosis type 2 or schwannomatosis. The purpose of this study was to assess the frequency of plexiform schwannoma by location, to determine their syndromic association, and to analyze the clinicopathologic features of tumors affecting the head and neck region. It was found, in this not entirely random population, that plexiform schwannoma represented 4.3% of all schwannomas, 23% of head and neck region examples, 15% of cutaneous schwannomas, and lastly, 2% of 322 oral nerve sheath tumors made separately available for review. Furthermore, the association with neurofibromatosis type 2 and with schwannomatosis was 5% each.