Benign plexiform (multinodular) schwannoma: a rare tumour unassociated with neurofibromatosis

Case report and literature review: plexiform schwannoma in the penile and inguinal region in a child

Penile schwannoma is an uncommonly seen peripheral nerve tumor, of which penile plexiform schwannomas (PS) is extremely rare that has only been reported in several adults. We present a case of penile PS with a similar lesion in inguinal region in a 9-year-old child, which appeared as painless masses and rapidly growing within one year. Penile ultrasonography suggested well-defined lesions with limited vascularity. Both masses presented with low-to-intermediated signal intensity and no definite enhancement in computed tomography. The lesions were completely resected with minimal intraoperative bleeding, and a diagnose of benign PS was confirmed based on H&E staining and positive S-100 expression in immunohistochemistry. There was no evidence of tumor recurrence or metastasis after 6 months of follow-up. Only 6 cases of penile schwannoma in children were recorded, of which 5 were malignant, and none was PS. The malignancy rate of penile schwannoma in children may be overestimated due to delayed diagnose of benign ones. A rapidly growing penile mass with a suspected metastatic lesion in inguinal region could be easily misdiagnosed as malignant. This case report and literature review is expected to assist clinicians in getting a comprehensive understanding of children penile schwannomas and choosing the best management strategy when faced with this rare condition.

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).

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.

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.

A case of peripancreatic plexiform schwannoma

Background

Plexiform schwannoma is one of the least common variants of schwannoma, accounting for only 5% of all schwannoma cases. It generally occurs in the skin and subcutaneous tissues and is uncommon in deep soft tissue or viscera. We present an extremely rare case of plexiform schwannoma arising from the peripancreatic plexus.

Case presentation

A 29-year-old man presented with hyperglycemia detected during a medical checkup. He was diagnosed with type 1 diabetes based on the clinical findings and laboratory tests. During the diagnostic process for diabetes, a 2.5 cm mass was incidentally detected in the pancreas by abdominal ultrasound. Contrast-enhanced computed tomography revealed a mass that was gradually enhanced at the body and tail of the pancreas. Magnetic resonance imaging revealed low signal intensity of the mass on T1-weighted images and high signal intensity on T2-weighted and diffusion-weighted images. Magnetic resonance cholangiopancreatography showed no abnormal findings in the main pancreatic duct. Endoscopic ultrasonography (EUS) showed a lobulated, low-echoic mass with a clear boundary. EUS-guided fine needle biopsy was performed, and spindle-shaped cells that were diffusely immunopositive for S-100 and negative for c-kit and desmin were detected, resulting in a diagnosis of a neurogenic tumor arising from the pancreas or the peripancreatic nerve plexus. The patient underwent laparoscopic spleen-preserving distal pancreatectomy. Although the tumor was connected to the splenic plexus, the splenic artery could be divided along its adventitial plane. Macroscopic findings of the excised tumor consisted of multiple yellowish-white nodules, and its histopathological features were consistent with plexiform schwannoma. There was no pancreatic tissue on the dorsal surface of the tumor, which suggested that the tumor arose from the peripancreatic nerve plexus.

Conclusions

The findings documented herein can aid in the differential diagnosis of peripancreatic schwannoma and in planning appropriate treatment.

Diagnosis of plexiform schwannoma of the foot in a 66-year-old male: a case report and literature review

Plexiform schwannoma is a rare tumor in the lower extremity which grows slowly and is noninvasive. The tumor size is usually less than 2 cm. The main affected population of this disease is concentrated on the age group of 20 to 50 years old. In this study, we reported a rare case of 66-year-old male with a large soft tissue mass on his right foot with a tumor size larger than 7 cm. The ultrasound was performed and showed circumscribed hypoechoic image, indicating a suspected diagnosis of lipoma. The subsequent MRI showed a multilobulated heterogenous signal on T2WI and STIR sequence with mild enhancement, suggesting hemangiomas. Then the tumor of the patient was removed for pathological examination and the results confirmed the diagnosis of plexiform schwannoma. Patient recovered well and had no recurrence in 9 months after the surgery. CT, MRI, and ultrasound are useful to distinguish these rare tumors from other soft tissue lesions, in contrast, MRI has higher sensitivity and provides more accurate diagnostic information. This case report provides a deep understanding of plexiform schwannoma. In the diagnosis of large soft tissue tumors in the lower extremity of the elderly, attention should be paid to the differential diagnosis of plexiform schwannoma to improve the diagnosis level.

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.

Intraneural Hybrid Neurofibroma/Schwannoma In Scalp: A Case Report

Benign Peripheral Nerve Sheath Tumours (BPNSTs) are traditionally classified into schwannoma, neurofibroma and perinurioma. Due to advances in molecular techniques, hybrid BPNSTs containing more than one histologic types have been documented. Recent studies have demonstrated their frequent association with inherited syndromes like schwannomatosis and neurofibromatosis. Intraneural variant of hybrid neurofibroma/schwannoma is yet to be described. Here we report such a case in a 30-year-old male, who presented with a scalp swelling and histology showed intraneural neurofibromatous tumour admixed with schwannoma-like nodules. IHC (immunohistochemistry) showed variable S100 staining in neurofibromatous areas, diffuse S100 staining in schwannoma-like areas and negative EMA staining in the tumour.

Oral plexiform schwannoma with unusual epithelial induction

Rare epithelial structures in benign nerve sheath tumors are almost always glandular in appearance. We describe a case of intraoral plexiform schwannoma with concurrent squamous epithelial hyperplasia. The lesion occurred as a pigmented nodule on the gingiva of a 35-year-old woman with no systemic involvement. Histologically, unencapsulated, plexiform fascicular proliferations of schwann cells could be traced from the submucosa to the lamina propria, finally making direct contact with heavily pigmented, elongated rete ridges of the overlying epithelium. Also noted was a schwannian network centered on clustered odontogenic epithelial rests of mature squamous-type, the number and size of which had markedly increased. Impressive immunoprofiles of periepithelial neural microfascicles included the complete absence of axon and perineurium and the unexpected presence of endoneurial fibroblasts. The repertoire of epithelial changes was in a confined area with no extension beyond, supporting hyperplasia induction by an underlying/surrounding schwannoma.

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.

Intraosseus plexiform schwannoma of the mandible: immunohistochemical differential diagnosis

Schwannomas and neurofibromas are the most common benign tumors derived from peripheral nerves, and whereas the head and neck region is the most common location for the occurrence of benign neural sheath neoplasms, origin within the oral cavity is uncommon, and occurrence centrally in the jaws is most unusual. Plexiform (multinodular) schwannoma is an anatomically unique variant of schwannoma characterized grossly and/or microscopically by intraneural plexiform and often multinodular growth. In current report, we present the first reported case of intraosseous plexiform schwannoma of the mandible, an extremely rare benign neurogenic tumor, diagnosed by optical and immunohistochemical procedures, showing the importance of differential diagnosis of these unusual intraosseous mandibular tumors.

Microcystic/reticular schwannoma of the pancreas: a potential diagnostic pitfall

Schwannomas occurring in the pancreatic head are rare benign non-recurring mesenchymal neoplasms and are reported to show classic morphologic features. Herein we report a case of a 62 year old male presenting with a 5 cm mass in the pancreatic head encasing the portal vein and the truncus coeliacus. Preoperative fine needle aspiration revealed malignant tumour cells consistent with a moderately differentiated adenocarcinoma. A Whipple surgery was performed after palliative chemotherapy. Histological evaluation revealed a multinodular unencapsulated tumour with focal infiltration into pancreas parenchyma and a striking microcystic/reticular growth pattern. Anastomosing and intersecting strands of spindle cells with eosinophilic cytoplasm set in a myxoid partly collagenous stroma were observed. The tumour cell nuclei were round oval and tapered and showed inconspicuous small nucleoli. Degenerative nuclear atypia was seen. Mitotic activity was sparse (1/50 HPF). Pleomorphism or necrosis was absent. The tumour cells showed strong nuclear and cytoplasmic positivity for S-100 protein, and focal positivity for glial fibrillary acidic protein. The diagnosis of a microcystic/reticular schwannoma was made. The awareness of and, to some extent, the knowledge about this rare tumour are needed to achieve the correct diagnosis and to avoid confusion, especially with malignant pancreatic neoplasms.

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.

Cutaneous plexiform schwannomas in a patient with neurofibromatosis type 2

Plexiform schwannoma is a rare benign neoplasm of the neural sheath characterized by a multinodular plexiform growth pattern. The tumor usually occurs as an isolated finding, although rare cases have been reported in association with neurofibromatosis type 2 (NF2). A 25-year-old man was admitted for foot drop. He had an asymptomatic skin-colored nodule on his neck that had been present for 10 years. His medical history included local excision of a plexiform schwannoma on his left leg in our dermatology clinic 6 years prior. A histopathological examination of the skin-colored nodule also showed the typical microscopic features of a plexiform schwannoma, including the characteristic Antoni type A areas showing frequent nuclear palisading and Verocay bodies. Magnetic resonance imaging revealed a meningioma and a vestibular schwannoma in the cranium and multiple neurofibromas on the spinal cord. Herein we report a rare case of cutaneous plexiform schwannomas in a patient with NF2.

Plexiform schwannoma of the ulnar nerve

Plexiform schwannoma is a rare benign neurogenic tumour; we report a case that arose in the ulnar nerve of a 59-year-old woman. Exploration showed a continuous multinodular tumour that involved the ulnar nerve from the hand to the upper arm; the length of the tumour was 35 cm.

Microcystic/reticular schwannoma: a distinct variant with predilection for visceral locations

Schwannomas are benign, generally nonrecurring tumors most frequently arising in the subcutaneous tissue of adults with no sex predilection. Herein we report 10 cases of a distinctive morphologic variant of schwannoma with predominantly microcystic-reticular morphology and characterize the clinicopathologic spectrum. The age at presentation ranged from 11 to 93 years (median age 63 y). The tumor size ranged from 0.4 to 23 cm (median size 4.3 cm). Five tumors arose in the gastrointestinal tract, most often in the submucosa. Two cases arose in subcutaneous tissue and 1 case each in the upper respiratory tract, the adrenal gland, and deep soft tissue. None of the patients had features of neurofibromatosis type 1 or type 2 (NF1, NF2). Histologically 8 tumors were circumscribed but unencapsulated and 2 cases located in the subcutaneous fat were circumscribed and encapsulated. At visceral locations, focally pushing margins and microscopic foci of infiltration into surrounding parenchyma were seen. All cases showed a striking microcystic and reticular lesional growth pattern with anastomosing and intersecting strands of spindle cells with eosinophilic cytoplasm distributed around islands of myxoid or collagenous/hyalinized stroma. The nuclei were round, oval, and tapered and showed inconspicuous nucleoli. Three cases had smaller areas resembling conventional schwannoma. Mitotic activity did not exceed more than 3 mitoses/50 high-power fields (HPF) (median 1/30 HPF). Pleomorphism and necrosis were absent. All tumors showed strong nuclear and cytoplasmic positivity for S-100 and variably strong glial fibrillary acidic protein staining. A surrounding tumor capsule was highlighted with epithelial membrane antigen in 2 out of 10 cases. Smooth muscle actin, Desmin, Pan-CK, AE/AE3, Cam5.2, and p-63 were negative in all cases evaluated. Neurofilament protein highlighted axons in one out of 7 cases investigated. CD117 showed weak focal positivity in 1 out of 4 cases. Follow-up data were available in 7 cases (median duration 15 mo). None has recurred to date. Microcystic schwannoma represents a distinctive morphologic variant of schwannoma with predilection for visceral locations. Recognition of this distinct entity is essential to avoid confusion with malignant tumors, especially in the gastrointestinal and upper respiratory tracts.

Cutaneous plexiform schwannoma of the finger not associated with neurofibromatosis

Plexiform schwannoma is a rare, benign, peripheral nerve sheath tumor that occurs as an uncommon nodular variant of schwannoma. It is important to recognize this tumor because it can be misdiagnosed as plexiform neurofibroma. In contrast to the latter, however, plexiform schwannoma is not associated with neurofibromatosis (von Recklinghausen disease). We report a case of plexiform schwannoma located on the index finger of a 20-year-old male patient with no signs of neurofibromatosis.

The controversial nosology of benign nerve sheath tumors: neurofilament protein staining demonstrates intratumoral axons in many sporadic schwannomas

Schwannomas are benign peripheral nerve sheath tumors believed to be composed purely of cells with ultrastructural features of Schwann cells; these tumors are believed to develop eccentrically from the surface of nerves and not to contain axons, other than immediately beneath the capsule. This concept has recently been disputed in cases associated with neurofibromatosis type 2. The usual presence of intratumoral axons in neurofibromas is said to allow easy distinction from schwannomas. Eighty sporadic schwannomas (20 conventional, 20 cellular, 20 ancient, 10 gastric, and 10 plexiform) were retrieved from the authors' files. Hematoxylin-and-eosin stained slides were reviewed, diagnoses were confirmed and all tumors were stained for S-100 protein and neurofilament protein (NFP). The amount (rare, focal, multifocal, and diffuse) and distribution (central and/or peripheral) of axons within the tumors were analyzed. All tumors were strongly and diffusely positive for S-100 protein (nuclear and cytoplasmic staining). NFP-positive axons were identified in 11 of 20 (55%) conventional schwannomas (2 rare, 4 focal, 3 multifocal, and 2 diffuse; 5 central, 4 peripheral, and 2 central and peripheral) and in 15 of 20 (75%) cellular schwannomas (3 rare, 6 focal, and 6 multifocal; 12 central, 1 peripheral, and 2 central and peripheral). Of the 20 ancient schwannomas, 7 cases (35%) showed intratumoral axons, highlighted by NFP immunostaining (1 rare, 4 focal, 1 multifocal, and 1 diffuse; 4 peripheral, 2 central, and 1 central and peripheral). Most cases of gastric schwannoma showed no evidence of intratumoral axons; 9 cases (90%) were negative for NFP and only 1 case (10%) was positive (focal and central). Seven of 10 cases (70%) of plexiform schwannomas were negative for NFP, whereas only 3 cases (30%) showed positive axons (2 multifocal and 1 focal; 3 central). The unexpected but quite frequent presence of intratumoral axons in schwannomas argues against conventional views of these lesions' pathogenesis as an eccentric encapsulated lesion and raises the possibility that a more diverse cell population, perhaps more closely resembling neurofibromas, may constitute these neoplasms. Although NFP-positive axons were most often present in the conventional and cellular variants of schwannoma, their presence was also observed in a minority of ancient, gastric and plexiform schwannomas. Differentiation between neurofibroma and schwannoma in cases with overlapping cytoarchitectural features should not be based solely on the presence or absence of NFP-positive axons within a given tumor.

[Plexiform schwannoma of the delto-pectoral area]

Plexiform schwannoma is a form of schwannoma which usually involves cutaneous tissues. It cannot be easily differentiated from malignant tumors, especially deep or cellular lesions. We report a deep plexiform schwannoma which we place among the various benign or malignant nerve sheath tumors, which may or may not develop within the context of genetic disease. Finally, the differential diagnoses are discussed. Recognition of the lesion is necessary for appropriate treatment.

Intra-extradural plexiform schwannoma of the cervical spine

STUDY DESIGN

Case report.

OBJECTIVE

To describe the clinical and radiographic features of an extremely rare case with intra-extradural plexiform schwannoma of the cervical spine.

SUMMARY OF BACKGROUND DATA

Plexiform schwannoma is a rare neurogenic tumor that predominantly occurs in the dermis and subcutis. Noncutaneous deep-seated lesions have rarely been described. No cases of intra-extradural plexiform schwannoma of the cervical spine have previously been reported.

METHODS

A 16-year-old boy presented with a 3-month history of left neck and shoulder angle pain, motor weakness of the left upper extremity, clumsiness of bilateral hands, and mild gait disturbance. Preoperative magnetic resonance imaging showed a multinodular inhomogeneous dumbbell-shaped tumor encroaching on the cord at C3-C4. T1-weighted imaging showed the tumor as inhomogeneous with slightly higher intensity than muscle. T2-weighted imaging demonstrated a multinodular inhomogeneous tumor with much higher intensity than muscle, and each nodule of the tumor displayed a peripheral rim of higher intensity and central relatively lower intensity.

RESULTS

Through hemi-laminectomy from C3-C4 and facetectomy of the left side of C3-C4, the intradural parts of the multinodular tumor were completely extirpated and extradural parts of the multinodular tumor were enucleated as much as possible. Gross examination of the tumor showed yellowish-white soft contents that were encapsulated and multilobulated. Histologic examination revealed benign schwannoma. After surgery, preoperative neurologic symptoms completely resolved.

CONCLUSION

To the best of our knowledge, this is the first reported case of intra-extradural plexiform schwannoma. Careful magnetic resonance imaging might be helpful in suggesting this rare plexiform schwannoma before surgery.

Contiguous conventional and plexiform schwannomas

✓The authors present clinical, imaging, and histological features of two adult patients found to harbor a conventional schwannoma contiguous with a deep plexiform schwannoma. One patient had neurofibromatosis (NF) Type 2 (NF2), and both intracranial (bilateral oculomotor, trigeminal, acoustic, and hypoglossal schwannomas as well as meningiomas) and intraspinal (schwannomas and meningiomas) lesions. The proximal forearm lesions consisted of a conventional schwannoma and an underlying plexiform component. The second patient, who did not have NF2, presented with a similar enlarging mass in the distal arm; two contiguous lesions were resected. Both patients exhibited distinct, readily identifiable, magnetic resonance imaging features. Plexiform schwannomas are rare lesions that occur sporadically or, on occasion, in association with NF2 or meningiomas with or without multiple schwannomas. The authors believe that a more careful examination of patients with NF2 may show that these people have a higher incidence of plexiform schwannoma than previously thought. Pathological confirmation is crucial in distinguishing plexiform schwannomas from plexiform neurofibromas, because the latter are directly associated with NF1 and have a significant tendency to undergo malignant transformation. To the best of the authors’ knowledge, this is the first report of a conventional schwannoma contiguous with a deep plexiform schwannoma.

Pathologic classification of peripheral nerve tumors

Peripheral nerve tumors show an interesting histologic variety despite being composed ofa limited array of cellular constituents. As we learn more about the interplay between the Schwann cells, perineurial cells, and ganglion cells that comprise these tumors, it is likely that we will better understand the biologic behavior of these important tumors. Key issues for the pathologist include distinguishing schwannomas from neurofibromas, ganglioneuromas from neurofibromas involving ganglia, and MPNSTs from cellular schwannomas or neurofibromas. The association of each of these tumors with genetic tumor disorders provides a unique window into discovering basic mechanisms of cell regulation and tumorigenesis that may ultimately shed light on the biology of a much wider array of human disease.

Neurofibromatosis type 2 with multiple plexiform schwannomas

Multiple plexiform schwannomas (PS) or neurilemmomas are very rare nerve sheath tumors, showing multiple schwannomas of the skin and other soft tissues, brain, or spinal cord with histopathologic characteristic of interwoven Antonio-A type tissues(1) but without other signs of neurofibromatosis type 2 (NF2). Neurofibromatosis type 2 is much less common than neurofibromatosis type 1 (NF1), with a symptomatic prevalence of 1 in 210,000,(2) and, to the authors' knowledge, only six cases of NF2 with multiple plexiform schwannomas have been reported in the literature.(3-5) We report a rare case of multiple cutaneous plexiform schwannomas associated with characteristic features of NF2 including bilateral acoustic neurilemomas and intracranial meningioma.

Plexiform schwannoma

We present a case of plexiform schwannoma, a rare benign peripheral nerve sheath tumour characterized by a multinodular and plexiform growth pattern, that had slowly grown for 40 years on the trunk of a 64-year-old woman. Preoperative biopsy findings, such as a high cellularity and the extent of nuclear atypia of the tumour, led us to suspect a malignant peripheral nerve sheath tumour; but ultimately a benign plexiform schwannoma was diagnosed based on an immunohistochemical review of the excised tumour using various markers including S-100 and Ki67 (MIB1).

Case report: plexiform schwannoma of the vulva

We describe a case of plexiform schwannoma, a benign tumour of the peripheral nerve sheath, arising in the labia of a 5-year-old girl who presented with a mass in the vulva. Light and electron microscopy, special stains and immunohistochemistry studies were done on the excised specimen. A Medline search revealed a single case of vulvar plexiform schwannoma which was reported in 1983.

Abnormal pigmentation of schwannoma attributed to excess production of neuromelanin-like pigment

Five cases of non-melanotic pigmented schwannoma with excess accumulation of neuromelanin are presented. The tumors were composed basically of spindle or fusiform tumor cells, compatible with those of classical schwannoma, together with varying numbers of tumor cells containing various amounts of light brown or grayish pigment. Fontana-Masson stain demonstrated argentaffin granules in some tumor cells of each tumor and bleaching with potassium permanganate abolished argentaffin reaction. Ultrastructural examination demonstrated the granules contained fine particles with heterogeneous density, occasionally together with coarse granular materials or amorphous high-density areas, indicating lysosome or autophagosome. Neither typical melanosomes nor neurosecretory granules were detected. In immunohistochemistry, neurogenic markers as well as CD68 were expressed in most tumor cells in each case and various numbers of tumor cells were positive for Leu7 and CD34. Lysozyme was also frequently positive in tumor cells, especially in granular cells. HMB45 was not expressed in any of the cases. These findings indicate that these cases are schwannomas with abnormal accumulation of neuromelanin-like pigment.

Plexiform spitz nevus: an intradermal spitz nevus with plexiform growth pattern

Two cases of a distinctive variant of Spitz (spindle and epithelioid cell) nevus are described. One lesion developed on the lower leg of a 17-year-old boy and the other lesion on the back of a 52-year-old man. The microscopic appearance was characterized by a plexiform arrangement of bundles and lobules of enlarged spindle to epithelioid melanocytes throughout the superficial and deep dermis. Intraepidermal melanocytic proliferation was unappreciated. Some lobules were circumscribed by a thin rim of compressed fibrous tissue. In both cases a myxoid stroma was present. The cells had abundant eosinophilic cytoplasm with well-defined borders. The nuclei were enlarged, consistently ovoid and vesicular, with small nucleoli. Both cases contained scattered multinucleate giant cells similar to those observed in classical form of Spitz nevi. No melanin pigment was detectable by light microscopy. No mitoses were observed in one case and a rare mitosis was present in the other. Tumor cells were strongly immunoreactive for S-100, but not for HMB-45, desmin, and actin. The differential diagnosis of this distinctive tumor includes desmoplastic/neurotropic melanoma, plexiform spindle cell nevus, cellular blue nevus, plexiform neurofibroma, and cellular neurothekeoma. The designation of "plexiform Spitz nevus" is chosen to emphasize its distinctive plexiform growth pattern.

Plexiform schwannoma of the neck extending deeply to the mediastinum

We describe a 42-year-old man who had tumors occupying the right deep neck through the upper part of the mediastinum. The right vocal cord was fixed and bulgings of the pharyngeal and tracheal wall were observed. At surgery, the masses were subtotally removed as much as possible. Histological examination revealed that they were schwannomas. The postoperative course was uneventful, except for the presence of hoarseness.

Schwannoma with features mimicking neuroblastoma: report of two cases with immunohistochemical and ultrastructural findings

OBJECTIVE

A study of two cases of a rare variant of benign schwannoma showing areas mimicking neuroblastoma/peripheral primitive neuroectodermal tumour (PNET).

METHODS

Sections of formalin fixed, paraffin embedded specimens were studied by tinctorial stains and immunohistochemistry, and the tissue retrieved from formalin was examined by electronmicroscopy in one case.

RESULTS

The tumours were small and subcutaneous. Both showed features of benign schwannoma; one had a multinodular plexiform pattern. In addition, rosette-like structures consisting of collagenous cores surrounded by small round cells or slightly larger epithelioid cells were present. Tumour cells were positive for S100 protein, Leu7, and in one case GFAP, but were negative for neurofilament protein, synaptophysin, and MIC2. Type IV collagen surrounded individual cells. Electronmicroscopy in case 2 confirmed schwannian features (lamina, processes) and failed to show features of neuroblastoma (neuroendocrine granules).

CONCLUSIONS

Benign schwannomas may contain rosette-like structures mimicking neuroblastoma/PNET. The techniques used confirmed schwannian differentiation only and eliminated neuroblastoma/PNET. These uncommon variants should be recognised by practising histopathologists to avoid erroneous diagnoses and inappropriate treatment.

Benign epithelioid schwannoma

Benign schwannoma (neurilemoma) has various morphologic patterns that may cause problems in differential diagnosis. Although an epithelioid variant of malignant schwannoma simulating carcinoma and melanoma is well recognized, a benign counterpart has not yet been defined. In the current study, we describe five cases of benign epithelioid schwannoma that were in the subcutis (four cases) and the neck of the urinary bladder (one case). The tumors occurred in adults 28-73 years of age, were 1-4.5 cm in diameter, were well circumscribed and cellular, and were composed of epithelioid cells arranged in cords and nests. The benign nature of the lesions was evident by a constellation of features, including small size, sharp circumscription, bland morphology, low proliferative activity (four of five had < or =1% Ki67 immunostaining), and a benign clinical course after either marginal or intralesional excision. All cases had some features of classic schwannoma light microscopically and a high degree of Schwann cell differentiation both ultrastructurally and immunohistochemically. The recognition of benign epithelioid schwannoma is important because it may be misinterpreted as a malignant neuroectodermal, mesenchymal, epithelioid, or melanocytic tumor.

Phenotypic diversity of neurofibromatosis 2: association with plexiform schwannoma

AIMS

Plexiform schwannoma (PS) is a rare variant of benign schwannoma characterized by a multinodular and plexiform growth pattern. In contrast to plexiform neurofibroma. PS is not associated with neurofibromatosis 1 (NF-1; von Recklinghausen's disease) and has no propensity for malignant transformation. The purpose of this study was to clarify the relationship between PS and the entities of neurofibromatosis 2 (NF-2; bilateral acoustic neurofibromatosis) and schwannomatosis.

METHODS AND RESULTS

Six cases of PS associated with NF-2 or meningioma were retrospectively studied clinicopathologically and immunohistochemically. Four cases of PS were found among the patients with NF-2, and all of these had multiple PSs; three cases also had multiple schwannomas of the spinal nerve roots and two of these had meningioma. Two other patients had meningioma, but not NF-2. Four patients were male and two were female. The ages ranged from 18 to 52 years (mean 29.6 years). Histologically, PS showed the histological features that have been previously described, i.e. schwannoma composed of a predominant Antoni A-type component with a plexiform growth pattern. Immunohistochemically, the tumour cells were positive for S100 protein. Each nodule was surrounded by perineural cells which were positive for epithelial membrane antigen.

CONCLUSIONS

It is important to recognize that PS could be associated with NF-2 or meningioma. The combination of PS and meningioma may be a 'formes frustes' of NF-2, and is clinically overlapped with schwannomatosis.

Cytogenetic and histologic correlation of peripheral nerve sheath tumors of soft tissue

Cytogenetic analysis was performed on 11 peripheral nerve sheath tumors of soft tissue from 10 patients. They include 6 benign and 5 malignant schwannomas. Five cases which include two benign, one cellular and two malignant schwannomas had a known association with a nerve, but only one patient with malignant schwannoma has clinically documented neurofibromatosis type I. All the patients had a normal diploid constitutional karyotype. Two cases of cellular schwannoma were analyzed by routine cytogenetic analysis and fluorescence in situ hybridization (FISH). One tumor was karyotyped as 45, XX,-13,-22 +mar; and the other case had a 45,X,-Y,t(1;17) (p12;q11.2) karyotype. In the latter, the breakpoint in 17q occurred below the centromere and is at or in the region of the Neurofibromatosis Type 1 (NF1) gene. Four benign tumors had a normal diploid karyotype. One hypodiploid malignant schwannoma with myxoid features demonstrated monosomy of chromosomes 17 and 22 by FISH analysis. The rest of the malignant schwannomas showed a wide range of numerical and structural aberrations, with frequent loss of 22q and gains of chromosomes 2 and 7. Loss of a sex chromosome was observed in cellular as well as malignant schwannomas. Regional karyotypic evolution was noted in one malignant schwannoma. Cytogenetic analysis may prove to be useful in identifying tumors, such as cellular schwannomas, which, because of their histologic features may be inadvertently categorized as malignant. Simultaneous involvement of NF1 and NF2 genes, which are located on chromosomes 17q and 22q, respectively, should be investigated at a molecular level in both benign and malignant tumors of peripheral nerves.

Cutaneous plexiform schwannoma associated with neurofibromatosis type 2

BACKGROUND

Plexiform schwannoma (PS) is a rare benign tumor of the nerve sheath that can be located either in the deep soft tissues or in the dermis or subcutis. The tumor predominantly affects young adults and occurs most commonly as a slowly growing asymptomatic solitary nodule in the head and neck region, trunk, and upper extremities.

METHODS

A cutaneous PS located in the preauricular region of a 19-year-old white female is reported. The patient exhibited six "café-au-lait" spots in the trunk and the extremities. Magnetic resonance imaging examination showed bilateral tumors in both acoustic nerves (considered schwannomas) and also masses in the right major sphenoidal wing, falx, and T2-T3 level of rachis and a solid and cystic tumor in the low medulla oblongata. Tumors of the preauricular region, medulla oblongata, spinal cord at level T2-T3, and major sphenoidal wing area were surgically removed. The tumors were studied by immunohistochemistry and diagnosed as PS, pilocytic astrocytoma, and meningiomas, respectively.

RESULTS

Seventy-eight cases of PS have been reported in the literature: 8 (10.2%) have been associated with clinical schwannomatosis, 6 (7.7%) with multiple cutaneous schwannomas syndrome, and only 3 (3.8%) with neurofibromatosis type 1 (NF-1).

CONCLUSIONS

In this report, to the authors' knowledge, for the first time PS is described associated with neurofibromatosis type 2. The tumor does not appear to have significant association with NF-1. Plexiform schwannoma should be recognized because it may be misdiagnosed as plexiform neurofibroma or other plexiform malignant tumors. Differentiation from plexiform neurofibroma is important, because the latter is virtually pathognomonic of neurofibromatosis type 1 and has a propensity for malignant transformation.

Multinodular versus plexiform neurilemoma of the hard palate. Report of a case

Neurilemoma (schwannoma) is the most commonly encountered nerve sheath tumor of the oral cavity. It generally appears as a single encapsulated nodule that occasionally causes pain or discomfort. The tongue is involved most frequently, followed by the palate, floor of mouth, and buccal mucosa. Neurilemomas occur most often during the second or third decades of life. Our patient is a 21-year-old woman with a recurrence of a palatal mass that was excised 3 years earlier. Histologically the lesion appeared to be a multinodular neurilemoma, a pattern rarely reported in the oral cavity.

Cutaneous plexiform schwannoma in a pig

A plexiform schwannoma (PFS) observed as a solitary mass in the dermis of a 6-month-old pig consisted of schwannoma cells of Antoni A type and B type. Neoplastic cells in Antoni A type areas sometimes showed cord-like outgrowths or a neurofibromatous pattern. Neoplastic cells in Antoni B type areas showed erythrophagocytosis, some encircling the microvasculature. Immunohistochemically, neoplastic cells were strongly positive for S-100 protein and vimentin. Peripheral parts of the nodules were cytokeratin (clone AE1/AE3)-positive, as in normal swine perineurial cells. Double immunostaining clearly demonstrated neoplastic cells doubly positive for both S-100 protein and cytokeratin, suggesting that S-100-positive Schwann cells and cytokeratin-positive perineurial cells are functional variants of the same cell type. Ultrastructurally, neoplastic cells in Antoni A type areas possessed characteristics of Schwann cells, such as cytoplasmic interdigitation, external laminae and intercellular junctions. At the periphery of the nodules, features of perineurial cells were detected. Neoplastic cells in Antoni B type areas seemed to be undergoing degenerative processes similar to those in Antoni A type regions and they contained many lysosomes. The neoplasm was generally similar in both location and histology to that seen in man, but there were some histological, immunohistochemical and ultrastructural differences. This is the first reported case of PFS in domestic animals.

Plexiform schwannoma. Immunohistochemistry of Schwann cell markers, intermediate filaments and extracellular matrix components

An immunohistochemical study using a comprehensive panel of antibodies to Schwann cell markers, intermediate filaments and extracellular matrix components has been performed on three cases of plexiform schwannoma. All tumour cells expressed S 100 protein, Leu 7-HNK 1 antigen and vimentin; glial fibrillary acidic protein was detected in many tumour cells. In addition, expression of cytokeratin was also demonstrated in one case. The associated extracellular matrix was found to be reactive with antibodies to laminin, heparan sulfate proteoglycan, fibronectin, type I, III, IV and VI collagen. It is concluded that Schwann cells producing their own extracellular matrix are the main components of these tumours. The significance of the cytokeratin expression and the possible role of the extracellular matrix in regulating Schwann cells' proliferation in peripheral nerve tumours are discussed.

The new WHO classification of brain tumours

The new edition of the World Health Organization (WHO) book on 'Histological Typing of Tumours of the Central Nervous System' reflects the progress in brain tumour classification which has been achieved since publication of the first edition in 1979. Several new tumour entities have been added, including the pleomorphic xanthoastrocytoma, central neurocytoma, the infantile desmoplastic astrocytoma/ganglioglioma, and the dysembryoplastic neuroepithelial tumour. The list of histological variants has also been expanded. In line with recent morphological and molecular data on glioma progression, the glioblastoma is now grouped together with astrocytic tumours. The classification of childhood tumours has been largely retained, the diagnosis primitive neuroectodermal tumour (PNET) only being recommended as a generic term for cerebellar medulloblastomas and neoplasms that are histologically indistinguishable from medulloblastoma but located in the CNS at sites other than the cerebellum. The WHO grading scheme was revised and adapted to new entities but its use, as before, remains optional.

Unusual benign neurogenic soft tissue tumour. Epithelioid schwannoma or an ossifying fibromyxoid tumour?

An unusual form of subcutaneous soft tissue tumour with benign character is reported. The tumour was composed of uniform cells which were epithelioid in appearance. True myxoid matrix, osteoid formation or metaplastic bone were not present. Immunohistochemically S-100 protein and vimentin was demonstrated in the tumour cells. Electron microscopic examinations showed fragmented or continuous basal lamina, interdigitating cytoplasmic projections, myelin-like figures and a few cell junctions. The immunohistochemical and electron microscopic results indicate that the tumour is of Schwann's cell origin. Based on light microscopic, electron microscopic and immunohistochemical results we think our case is an epithelioid benign schwannoma but the non-ossifying form of fibromyxoid tumour of the soft parts cannot be excluded with confidence.

Plexiform and other unusual variants of palisaded encapsulated neuroma

Palisaded, encapsulated neuroma (PEN) has been described as a predominantly solitary, nodular tumor; plexiform or multinodular growth patterns have not been reported in detail. We reviewed 55 PEN in order to evaluate: 1) the predominant growth patterns; 2) features that may indicate previous trauma; and 3) association with acne-like changes. Sixteen cases (29%) had growth patterns other than the solitary, nodular type. These patterns were: a) plexiform (7/16), b) multinodular (5/16), and c) fungating (4/16). Other unusual features included evidence of trauma, i.e., fibrosis, myxoid change, chronic inflammation (5/16), partially incomplete capsule (6/16), and association with acne-like features (13/16). These results suggest that: 1) plexiform or multinodular growth patterns occur relatively often in PEN; 2) some changes indicate a possible histogenetic relation to traumatic neuroma, probably via secondary traumatization; 3) a high frequency of association with acne-like changes which could imply, but does not prove, an acne-induced histogenesis; and 4) the differential diagnosis of cutaneous plexiform lesions should include PEN.