Benign Epithelioid Peripheral Nerve Sheath Tumors of the Soft Tissues

Hybrid Epithelioid Schwannoma/Neurofibroma: A Report of 3 Cases

ABSTRACT

Peripheral nerve sheath tumors can include neurofibroma, schwannoma, and perineurioma, with hybrid nerve sheath tumor (HNST) being rare. We describe 3 HNST cases with epithelioid schwannoma and neurofibroma features, an uncommon manifestation of hybrid schwannoma/neurofibroma. The 3 cases involved the upper back, forearm, and thigh. Histopathologically, the tumors were located in the subcutis or dermis and subcutis. The epithelioid schwannoma component showed nests/cords of epithelioid cells with round nuclei and abundant cytoplasm. In contrast, the neurofibroma component showed spindle cell proliferation within myxoid stroma. The 3 cases showed variable proportions of both components. Immunohistochemically, the epithelioid schwannoma components were positive for S100 protein and negative for CD34, whereas the neurofibroma component showed partial S100 immunoreactivity and contained abundant CD34-positive cells with a fingerprint pattern. Epithelial membrane antigen and GLUT1 revealed the perineurial capsules. In conclusion, our cases expand the morphologic spectrum of HNST and underscore the importance of recognizing this variant.

Atypical Epithelioid Schwannoma in a Young Female- A Dilemma Set by Morphology; Resolved by Immunohistochemistry-A Rare Case Report

Epithelioid morphology spawns myriad of benign and malignant tumors into differential diagnoses, which include epithelioid sarcoma, malignant melanoma, epithelioid malignant peripheral nerves sheath tumor, epithelioid hemangioendothelioma, myoepithelioma, etc. Epithelioid schwannoma (ES), especially the atypical variant has not received much attention in literature. Conclusive diagnosis, important for accurate management is, however, challenging. We describe a case of atypical ES in a 24-year-old female. On clinical and radiological examination, a provisional diagnosis of vascular malformation was made. Atypical epithelioid ESs are rare, but it is important to be aware of this variant to avoid misdiagnosis with other malignant epithelioid tumors. Apart from clinical and morphological features, immunohistochemistry aids in arriving at a decisive diagnosis. Perineurium-like capsule, circumscription, oblong shape of the lesion, and hyalinized blood vessels are pointers toward shwannomatous differentiation of this tumor.

Histopathological Variants of Cutaneous Neurofibroma: A Compendious Review

The first description of histopathological variants of neurofibroma dates back to 1994. Over the years, many individual case reports elucidating unusual histologic features in neurofibroma have been added to the literature, some of which have defined criteria, with the others falling under the roof of benign neural neoplasms. These unusual features, which sometimes may lead to pauses in identifying a common benign tumor such as neurofibroma. Awareness of these variants may help dermatopathologists avoid misinterpretation. Thus, this review aims to summarize all novel and unusual histopathological variants of cutaneous neurofibroma reported to date, in addition to any unusual variants that we encountered in our practice.

Permanent neurological deficit caused by misdiagnosis of a giant intrapelvic sciatic schwannoma: A case report

Sciatic schwannomas (SSs) are extremely rare, and most are benign. Herein, we report a case of giant SSs in a woman who presented with abdominal pain. Because of the pain pattern and auxiliary examination findings, the patient was initially diagnosed with an ovarian cystadenoma. Magnetic resonance imaging (MRI) revealed an intrapelvic tumor. Histopathological examination confirmed that the mass was a benign intrapelvic schwannoma. Two days after complete tumor resection, the patients experience impaired mobility of the right lower limb. The tumor was 7 × 5.5 × 5 cm³ in size and in contact with the sacrum. The patient was followed up for up to 2 years. No evidence of recurrence was observed in the MRI scan. Severe damages to the sciatic nerve during surgery resulted in permanent neurological deficits. Hence, we also discuss the diagnostic tools and treatments for intrapelvic SSs, as well as the importance of careful radiological examination and multidisciplinary collaboration.

Epithelioid schwannoma: imaging findings on radiographs, MRI, and ultrasound

Epithelioid schwannoma is an uncommon benign peripheral nerve sheath tumor, with distinct morphological and pathological features. To our knowledge, the imaging features of epithelioid schwannoma have not been described. In this case report, we describe the imaging findings of a pathologically proven case of epithelioid schwannoma presenting as a slowly growing painless mass near the ankle. The MR imaging signs commonly associated with conventional schwannoma were absent. On correlative radiographs, there were intra-tumoral calcifications. Radiographs are an essential tool in the imaging evaluation of soft-tissue masses. Knowledge of soft-tissue tumor types that can be associated with intra-tumoral calcifications is helpful in honing the differential diagnosis.

Benign epithelioid peripheral nerve sheath tumour arising in the rectum: A cytological and histological description

A 57-year old man presented with a 3.6 cm submucosal rectal cystic mass detected on colonoscopy and MRI. The lesion was deroofed, with rectal cyst fluid and cyst wall received for examination. Smears contained atypical cells occurring singly and in small aggregates, with epithelioid and spindled cells with hyperchromatic nuclei. Occasional cells exhibited intranuclear cytoplasmic inclusions. The concurrent histopathology specimen from the rectal cyst wall showed good correlation with the cytologic findings. The lesion was confined to the muscularis propria, with predominantly epithelioid cells and occasional spindled forms arranged in sheets, nests, and trabeculae with intervening fibrillary and fibrous stroma. Mitotic figures were scant, with no atypical mitoses or necrosis. An extensive immunohistochemical panel was performed, showing strong and diffuse nuclear and cytoplasmic staining with S100 and moderate to strong intensity nuclear staining with SOX10, in keeping with a benign epithelioid peripheral nerve sheath tumour. The patient remains well 3 years following diagnosis, and two subsequent biopsies at the site show no evidence of recurrent disease. We herein provide the first cytologic description of this lesion, with histopathologic correlation and a brief review of other differential diagnostic possibilities.

Update on Peripheral Nerve Sheath Tumors

Recent work has revealed SMARCB1/INI1 loss by immunohistochemistry in a subset of epithelioid schwannomas and explored the significance of cytologic atypia and increased mitotic activity in these tumors. Additional studies have evaluated the utility and limitations of histone H3K27 trimethylation in diagnosis of high-grade and low-grade malignant peripheral nerve sheath tumors. New terminology regarding nerve sheath tumors in neurofibromatosis type 1 patients was proposed during a 2016 conference to better define guidelines for classification of this group of tumors. This review highlights novel findings and practical applications relating to these topics in peripheral nerve sheath tumors.

Lumbar intraspinal microcystic/reticular schwannoma: Case report and literature review

RATIONALE

Microcystic/reticular schwannoma (MRS) is a rare histological variant of schwannoma which was initially described in 2008 with a predilection for the visceral organs. This distinct tumor had been reported to mainly affect gastrointestinal tract, subcutaneous and soft tissue, various glands and head and neck region. However, MRS involving spine is extremely rare.

PATIENT CONCERNS

The authors report the first case of MRS occurring in the lumbar (L) spinal canal of a 40-year-old male who presented with continuous pain and numbness in both feet for 2.5 years. Physical examination revealed weakness of lower extremities and hyperalgesia of both feet.

DIAGNOSES AND INTERVENTIONS

The findings of pre-operative investigation were suspicious for either a schwannoma or a spinal meningioma. Accordingly, total laminectomy, complete tumor resection, instrumentation and spinal fusion were performed. Post-operative histopathologic examination revealed a well-encapsulated neoplasm with reticular and microcystic growth pattern. Antoni A and Antoni B regions, Verocay bodies and hyalinized blood vessels were observed. And cytologic atypia, necrosis or mitosis was absent. Immunohistochemically, the tumor cells showed strong and diffuse positivity for S-100 as well as SOX 10. Therefore, a histopathological diagnosis of MRS was finally made.

OUTCOMES

The patient remains well with no evidence of recurrence at a 22-month follow-up.

LESSONS

This is the first case of MRS which is located in the L spinal canal. Awareness of this distinctive entity is helpful in preventing diagnostic pitfalls and making correct treatment strategies.

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.

Liponeurofibroma: Clinicopathological features and histogenesis

A neurofibroma is a common cutaneous benign tumor of neural origin. Various histological variants have been reported. Recently, sporadic reports of fatty variants have been reported but their clinicopathological features have not been well studied. The purpose of this study was to examine liponeurofibroma, and to report the distinctive clinicopathological features and histogenesis in comparison with the classic form. A retrospective study was performed on 130 cases. Immunohistochemical staining was performed for S100, factor VIIIa, perilipin and vascular endothelial growth factor. Masson's trichrome stain was also used. Intratumoral adipocytes were examined with transmission electron microscopy. Thirty-two (24.6%) cases were classified as liponeurofibroma on microscopic examination. This variant was more common in patients with neurofibromatosis type 1, older age and female sex. The most prevalent location was the head and neck. Intratumoral fat deposits showed differences in morphology and size compared with subcutaneous fat on light microscopy. Neurofibromatosis type 1 had the highest odds of fatty change in liponeurofibroma. In sporadic cases, fatty change can be caused by senescence, chronic injury, or tissue hypoxia secondary to internal or external stimuli. Further investigation is needed to identify the pathomechanism of fatty change in various cutaneous neoplasms, including neurofibroma.

Neural and neurogenic tumours of the gastroenteropancreaticobiliary tract

Neural lesions occur uncommonly in the gastroenteropancreaticobiliary tract. However, due to the growing number of screening colonoscopy procedures, polypoid neural lesions of the colon are being recognised increasingly and range from benign tumours to high-grade malignant neoplasms. Morphological variability of neural tumours can be wide, although some entities share pathological features, and, as such, these lesions can be diagnostically challenging. We review the spectrum of pathology of neural tumours in the gastroenteropancreaticobiliary tract, with the goal of providing a practical approach for practising surgical pathologists.

Soft Tissue Tumors of Uncertain Histogenesis: A Review for Dermatopathologists

The mesenchymal tumors discussed herein represent a heterogeneous group of neoplasms with distinctive morphologic, immunophenotypic, and molecular genetic features. These uncommon tumors often arise in the dermis and subcutis and can pose a major diagnostic challenge to dermatopathologists because they closely mimic melanoma, carcinoma, fibrous histiocytoma, schwannoma, or granulomatous inflammation. This article reviews the clinical presentation, histopathology, differential diagnosis, and diagnostic pitfalls of epithelioid sarcoma, clear cell sarcoma, perivascular epithelioid cell tumor, ossifying fibromyxoid tumor, pleomorphic hyalinizing angiectatic tumor, and hemosiderotic fibrolipomatous tumor. Associated molecular genetic findings are also briefly reviewed with an emphasis on their diagnostic usefulness.

Epithelioid schwannoma of the skin displaying unique histopathological features: a teaching case giving rise to diagnostic difficulties on a morphological examination of a resected specimen, with a brief literature review

Background

Epithelioid schwannoma as a rare variant poses a challenge to all pathologists, as this uncommon entity is extremely difficult to conclusively diagnose by morphological analyses on a resected sample alone owing to its unique histopathological features. However, few papers have described the detailed clinicopathological characteristics of epithelioid schwannoma.

Case presentation

A 65-year-old female presented with a history of a flat and slightly elevated firm and tan plaque accompanied by occasional tenderness, measuring 10 × 8 mm, in the right joint of her hand 1 year before resection. A gross examination of a locally resected specimen revealed an encapsulated nodular lesion, yellow-whitish in color, partly filled with blood. A microscopic examination showed that the tumor predominantly consisted of a solid proliferation of epithelioid cells having mildly enlarged and round to partially spindled nuclei and abundant vacuolated or clear cytoplasm with very few mitotic figures and modest nuclear size variation, associated with focal hyalinized, cystic and hemorrhagic degeneration. This well-demarcated tumor was surrounded by dense, hyalinized and layered fibrocollagenous stroma. Immunohistochemically, these tumor cells were diffusely positive for S-100 protein and had a very low MIB-1 labeling index, and type IV collagen was strongly reactive with reduplicated basal lamina of them. We ultimately made a diagnosis of cutaneous epithelioid schwannoma.

Conclusion

We should be aware that, since pathologists might misinterpret epithelioid schwannoma as other soft tissue tumors, including its malignant counterpart, a wide panel of immunohistochemical antibodies can be powerful supplementary tools for identifying a very rare entity of conventional schwannoma.

Epithelioid Schwannomas: An Analysis of 58 Cases Including Atypical Variants

The histologic features and outcome of 58 cases of epithelioid schwannoma were studied to determine the significance of atypical histologic features. Cases were retrieved from personal consultation files from 1999 to 2013. Patients (31 male and 26 female patients) ranged in age from 14 to 80 years (median, 38 y). Two patients had schwannomatosis 1. Tumors developed in the dermis/subcutis (n=56) or muscle (n=2) of the upper extremity (34.5%), lower extremity (34.5%), thorax/abdomen/back (18%), and less common anatomic locations including the scalp, neck, lip, and breast. They ranged in size from 0.25 to 4.5 cm (median, 2.0 cm). Typically circumscribed and surrounded by a perineurium, they comprised single or small groups of epithelioid schwann cells with a moderate amphophilic cytoplasm and occasional nuclear pseudoinclusions. Stroma varied from myxoid to hyalinized, often with thick-walled vessels (55 cases). Mitotic rate ranged from 0 to 9 mitoses/10 high-power field (HPF) (2.37 mm) in the most active areas (mean, 2 to 3 mitoses/10 HPFs). Thirteen cases (22%) were "atypical," defined by a high mitotic rate (≥3 mitoses per 10 HPFs) and nuclear size variation (≥3:1). All (56/56) expressed S100 protein; type IV collagen invested groups or individual cells (16/17). Melanoma markers were negative, except for melan A (1 case). Follow-up in 39 patients (median, 78 mo; range, 6 to 174 mo) indicated that 31 (79%) were alive without disease (including 9/13 atypical cases; median, 78 mo), 7 (18%) were alive with unknown status, and 1 patient had died of unrelated causes. One tumor recurred, but none metastasized. Epithelioid schwannomas, even those with atypical features, are benign and do not constitute a histologic continuum with epithelioid malignant peripheral nerve sheath tumors, which typically occur in deep soft tissues and have more anaplastic features.

N-methyl-N-nitrosourea-induced schwannomas in male Sprague-Dawley rats with a literature review of inducible and spontaneous lesions

N-methyl-N-nitrosourea (MNU) possesses peripheral nervous system carcinogenic activity in rats and induces benign and malignant schwannomas in systemic organs. In this retrospective study, we compared the characteristics of various immunohistochemical markers in MNU-induced schwannomas in male Crj:CD(SD)IGS rats including: vimentin (Vim), S100, p75 nerve growth factor receptor (LNGFR), CD57, pancytokeratin (CK), myoglobin, desmin and α smooth muscle actin (SMA). Single intraperitoneal exposures of 50 or 75mg/kg MNU in male rats at the age of 4 weeks induced schwannomas in 43 surviving and terminated rats up to 30-weeks-old. The incidence rate of neoplastic lesions was 37% (16 of 43 rats). Benign schwannomas (mesentery, pancreas, thymus) and malignant schwannomas (subendocardium, cardiac intramural, thoracic cavity, abdominal cavity, prostate), occurred in nine and seven rats, respectively. All neoplastic lesions were moderately or strongly positive for Vim, S100 and LNGFR proteins. Benign tumors were weakly positive and malignant tumors strongly positive for Ki-67, suggesting a high active proliferation rate of Schwann cell precursors. All lesions were negative for CD57, CK, myoglobin, desmin and SMA. This data may provide useful immunohistochemical information for the investigation of schwannomas in rat chemical carcinogenicity studies.

Peripheral Nerve Sheath Tumors

This article presents an overview of the diagnostic categories of benign and malignant nerve sheath tumors, including neuroma, neurofibroma, nerve sheath myxoma, perineurioma, schwannoma, and malignant peripheral nerve sheath tumor. The discussion emphasizes histologic patterns; ancillary studies, such as immunohistochemistry; and differential diagnoses. The information is of value to practicing pathologists in both community and academic settings.

Epithelioid malignant peripheral nerve sheath tumor: clinicopathologic analysis of 63 cases

Epithelioid malignant peripheral nerve sheath tumor (EMPNST) is rare and differs from conventional malignant peripheral nerve sheath tumor by showing diffuse S-100 protein positivity, infrequent association with NF1, and occasional origin in a schwannoma. Loss of INI1 expression is seen in a subset of tumors. The purpose of this study was to further define clinicopathologic features and outcome data in a large series of EMPNST. Sixty-three cases were identified in consultation files. The patient group consisted of 33 men and 30 women; the median age was 44 years (range, 6 to 80 y). One patient was reported to have NF1. One patient had 3 seemingly separate primary EMPNSTs during his 12-year clinical course. The median tumor size was 3.0 cm (range, 0.4 to 20 cm), and tumors were located most frequently on the lower extremity (30/63; 48%) and trunk (16/63; 25%). Most tumors were superficial (5 dermal, 38 subcutaneous); 15 were subfascial, and 5 were visceral. Microscopically, tumors comprised a relatively uniform but clearly atypical population of epithelioid cells. The majority of tumors demonstrated a multilobular growth pattern, with lobules and nests surrounded by myxoid and/or fibrous stroma. Tumor cells were round, polygonal, or ovoid and had round vesicular nuclei and abundant amphophilic to palely eosinophilic cytoplasm. Focal spindled morphology was seen in one third of cases. Most tumors (55/63; 87%) showed marked cytologic atypia with irregular vesicular nuclei and prominent nucleoli. Mitotic rate ranged from 1 to 46/10 HPF (median, 5/10 HPF); atypical mitotic figures were seen in 7 cases. Necrosis was present in 17 tumors. Twelve tumors were associated with a nerve. Nine tumors arose in a schwannoma (6 conventional type, 3 epithelioid) and 1 in a neurofibroma (in the NF1 patient). All tumors expressed S-100 protein, and the majority showed strong and diffuse staining (87%; 55/63). There was no expression of the melanocytic markers Mart-1/Melan-A (0/58), HMB-45 (0/57), and MiTF (0/9). Other immunohistochemical results included variable staining for GFAP (24/40; 60%) and EMA (4/29; 14%), whereas keratin was consistently negative (0/33). INI1 expression was lost in 67% of tumors examined (35/52). Most tumors were treated by surgical resection; 13 also received chemotherapy and/or radiation. Follow-up data were available for 31 cases and ranged in duration from 3 months to 20 years (median, 36 mo). Twenty-two patients have no evidence of disease at the time of follow-up. Nine patients developed local recurrence, 3 of whom were reported to be disease-free at the time of latest follow-up (44 mo, 19 y, and 20 y). Five patients developed distant metastases, and 4 patients died of disease (including 2 with unresectable recurrent tumors). Recurrence, metastasis, and disease-related death were observed independent of anatomic site or depth. In summary, EMPNST is a morphologically distinct variant that most commonly affects adults on the lower extremity or trunk, although a wide age range and site distribution are seen. Most tumors arise in superficial soft tissue, are diffusely S-100 positive, and two thirds show INI1 loss. On the basis of available follow-up information there is a comparatively low risk for recurrence and metastasis, irrespective of tumor depth.

Ossifying fibromyxoid tumor: a clinicopathologic analysis of 26 subcutaneous tumors with emphasis on differential diagnosis and prognostic factors

INTRODUCTION

Ossifying fibromyxoid tumor (OFMT) is rare and may present diagnostic difficulty. We describe 26 subcutaneous examples of OFMT emphasizing differential diagnosis and prognostic features.

METHODS

Histopathology and follow-up data from archival/consultation cases were reviewed. Prognostic features were assessed according to proposed criteria.

RESULTS

Patients (16 female, 10 male) ranged from 26 to 88 years (median 54). The tumors (median 2.3 cm, range 0.8-8.5) involved lower limb (11), trunk (7), head/neck (4), or arm (4). All showed combinations of corded, nested and trabecular patterns in a fibromyxoid stroma. Out of 26 cases 13 had peripheral ossification. Sixteen of 22 cases showed S100 protein expression. Nuclear grade was low (14); intermediate (8) and high (4) while cellularity was low (14); moderate (7) and high (5), with overall good interobserver agreement. Median mitotic rate was 3/50HPF (0-61). Five met criteria for malignant OFMT showing high nuclear grade or high cellularity and mitotic rate >2/50HPF or both. Thirteen OFMTs were atypical. Follow-up (16/26, median 45.5 months, range 8-108) showed that patients with typical OFMT (3) and atypical OFMT (9) remained disease-free. Three malignant examples of OFMT recurred and one metastasized to the lung. No deaths were recorded.

CONCLUSIONS

Our results validate proposed prognostic classification of OFMT. Dermatopathologists should be aware of this unusual superficial tumor given its potentially aggressive behavior.

Malignant epithelioid peripheral nerve sheath tumor with prominent reticular/microcystic pattern in a child: a low-grade neoplasm with 18-years follow-up

Malignant peripheral nerve sheath tumors (MPNSTs) constitute <2% of soft tissue neoplasms in children and display a wide histologic spectrum including low-grade and epithelioid variants, although most are high-grade spindle cell sarcomas. Here, we describe an unusual case of a large retroperitoneal epithelioid MPNST diagnosed in a 7-year-old girl without family history or clinical features of neurofibromatosis type 1. The patient was treated by repeated surgical interventions, polychemotherapy, autologous stem cell transplantation, and irradiation therapy. Over the years, she developed multiple disseminated abdominal recurrences but is currently alive with very slowly progressing disseminated intra-abdominal disease 18 years from initial diagnosis. Histologically, the tumor was composed of medium-sized polygonal and ovoid-to-spindled cells set within a copious myxoid matrix with a prominent reticular and microcystic pattern reminiscent of the recently described reticular/microcystic schwannoma. Immunohistochemistry revealed strong and diffuse expression of S100, CD56, CD57, collagen IV, and neuron-specific enolase, with negativity for perineurial cell markers (claudin-1, epithelial membrane antigen, and glucose transporter-1) and other lineage-specific mesenchymal and epithelial antigens. This unusual variant of low-grade MPNST must be differentiated from a variety of other entities, in particular benign perineurioma, myxoid neurofibroma, and benign reticular/microcystic schwannoma. Confinement of the recurrent disease to the abdominal cavity emphasizes the necessity of primary curative wide excision of this highly recurring but nonmetastasizing low-grade neoplasm.

p75NTR is highly expressed in vestibular schwannomas and promotes cell survival by activating nuclear transcription factor κB

Vestibular schwannomas (VSs) arise from Schwann cells (SCs) and result from the loss of function of merlin, the protein product of the NF2 tumor suppressor gene. In contrast to non-neoplastic SCs, VS cells survive long-term in the absence of axons. We find that p75(NTR) is overexpressed in VSs compared with normal nerves, both at the transcript and protein level, similar to the response of non-neoplastic SCs following axotomy. Despite elevated p75(NTR) expression, VS cells are resistant to apoptosis due to treatment with proNGF, a high affinity ligand for p75(NTR) . Furthermore, treatment with proNGF protects VS cells from apoptosis due to c-Jun N-terminal kinase (JNK) inhibition indicating that p75(NTR) promotes VS cell survival. Treatment of VS cells with proNGF activated NF-κB while inhibition of JNK with SP600125 or siRNA-mediated knockdown reduced NF-κB activity. Significantly, proNGF also activated NF-κB in cultures treated with JNK inhibitors. Thus, JNK activity appears to be required for basal levels of NF-κB activity but not for proNGF-induced NF-κB activity. To confirm that the increase in NF-κB activity contributes to the prosurvival effect of proNGF, we infected VS cultures with Ad.IκB.SerS32/36A virus, which inhibits NF-κB activation. Compared with control virus, Ad.IκB.SerS32/36A significantly increased apoptosis including in VS cells treated with proNGF. Thus, in contrast to non-neoplastic SCs, p75(NTR) signaling provides a prosurvival response in VS cells by activating NF-κB independent of JNK. Such differences may contribute to the ability of VS cells to survive long-term in the absence of axons.

Cutaneous benign epithelioid peripheral nerve sheath tumour: a rare entity

Benign epithelioid peripheral nerve sheath tumor, a rare entity is an umbrella term describing benign, neural origin tumors with epithelioid morphology. Clinically indistinguishable from other benign cutaneous lesions, histopathology offers the only source of accurate diagnosis. Morphologic mimics include many benign and malignant soft tissue lesions. Besides a predominant epithelioid component, the lesion can also show a fair share of spindle cells. A circumscribed nodular tumour of low mitotic activity, it often exhibits areas resembling schwannoma or neurofibroma. An awareness of this entity and its varied morphological aspects helps to arrive at the correct diagnosis and hence avoid unnecessary extensive surgical procedures. This case presents features of this benign tumor which occurred in a 47 years old man.

Proceedings of the 2013 Joint JSTP/NTP Satellite Symposium

The first joint Japanese Society of Toxicologic Pathology (JSTP) and National Toxicology Program (NTP) Satellite Symposium, entitled “Pathology Potpourri,” was held on January 29^th at Okura Frontier Hotel in Tsukuba, Ibaraki, Japan, in advance of the JSTP’s 29^th Annual Meeting. The goal of this Symposium was to present current diagnostic pathology or nomenclature issues to the toxicologic pathology community. This article presents summaries of the speakers’ presentations, including diagnostic or nomenclature issues that were presented, select images that were used for audience voting or discussion, and the voting results. Some lesions and topics covered during the symposium include: treatment-related atypical hepatocellular foci of cellular alteration in B6C3F1 mice; purulent ventriculoencephalitis in a young BALB/c mouse; a subcutaneous malignant schwannoma in a RccHan:WIST rat; spontaneous nasal septum hyalinosis/eosinophilic substance in B6C3F1 mice; a rare pancreatic ductal cell adenoma in a young Lewis rat; eosinophilic crystalline pneumonia in a transgenic mouse model; hyaline glomerulopathy in two female ddY mice; treatment-related intrahepatic erythrocytes in B6C3F1 mice; treatment-related subendothelial hepatocytes in B6C3F1 mice; spontaneous thyroid follicular cell vacuolar degeneration in a cynomolgus monkey; congenital hepatic fibrosis in a 1-year-old cat; a spontaneous adenocarcinoma of the middle ear in a young Crl:CD(SD) rat; and finally a series of cases illustrating some differences between cholangiofibrosis and cholangiocarcinoma in Sprague Dawley and F344 rats.

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.

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.

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.

Collagen-rich variant of benign epithelioid peripheral nerve sheath tumor of the skin

Schwannoma and neurofibroma account for the majority of cutaneous benign peripheral nerve sheath tumors and usually pose little diagnostic difficulty in their classic forms. In rare instances, however, benign peripheral nerve sheath tumors may display epithelioid morphology and lack otherwise usual features of schwannoma or neurofibroma, making classification difficult. These unusual changes may prompt consideration of other benign neoplasms or a malignancy. Benign epithelioid peripheral nerve sheath tumor (BEPNST) is a somewhat non-specific term recently proposed to describe these neoplasms of imprecise histogenesis. Also diagnostically challenging, rare BEPNST with unusual arrangements of extracellular collagen have been described and reported as neuroblastoma-like schwannoma and collagenous spherulosis. We report a unique case of cutaneous BEPNST with a peculiar arrangement of abundant extracellular collagen, different than the previously observed patterns. Specifically, the neoplastic cells in this tumor were nearly obscured by the collagen, which formed large nodules and compressed the majority of the few remaining tumor cells to the periphery of the lesion. This excessive collagen production emphasizes the importance of adequate sampling to ensure a correct diagnosis.

Unilateral congenital facial nerve paralysis secondary to a benign epithelioid peripheral nerve sheath tumor

OBJECTIVE

A benign epithelioid peripheral nerve sheath tumor is described in the setting of congenital facial nerve (FN) paralysis. This is the first reported case in the English literature.

PATIENT

A 10-month-old girl with unilateral congenital FN paralysis.

INTERVENTIONS

Auditory brainstem evoked potential study, gadolinium-enhanced magnetic resonance imaging, temporal bone computed tomography, and transmastoid FN decompression with tumor resection.

MAIN OUTCOME MEASURES

Follow-up for tumor recurrence and postoperative FN function.

RESULTS

The child underwent a transmastoid FN exploration with resection of a 0.6-cm spherical tumor analyzed to be a benign epithelioid peripheral nerve sheath tumor. There is no evidence of recurrence, and FN function was unchanged at 1 year postoperatively.

CONCLUSION

Benign epithelioid peripheral nerve sheath tumor can cause congenital facial nerve palsy.

Colocalized cellular schwannoma and plexiform neurofibroma in the absence of neurofibromatosis. Case report

The authors report on a patient without neurofibromatosis Type 1 or 2 (NF1 or NF2) and without evidence of schwannomatosis, who was found to have an unusual combination of nerve sheath tumors-a large cellular schwannoma and multifascicular involvement of a plexiform neurofibroma arising from the same site within the radial nerve and posterior cord of the infraclavicular brachial plexus. This case broadens the spectrum of combined pathological features of nerve sheath tumors. Genetic studies revealed a combined loss of neurofibromin and merlin in both regions and chromosome arm 22q deletion within the neurofibroma component only. The latter finding supports the suggestion that these were two different clonal neoplasms, and is consistent with a collision tumor pattern.

Plexiform Epithelioid Schwannoma:

Epithelioid schwannoma is rare but may pose a challenge in histopathologic diagnosis. In the present report, we describe a plexiform variant of epithelioid schwannoma in the skin of the breast of a 47-year-old woman.

Schwannome épithélioïde du nerf acoustique : une observation

Epithelioid schwannomas mainly affect peripheral nerves and are frequently malignant. They are rarely encountered intracranially. Only five cases involving the eight nerve have been reported in the literature. We report the sixth case of epithelioid schwannoma of the acoustic nerve diagnosed in a 57 year-old woman operated for neurinoma of the right cerebellopontine angle. The patient was readmitted for local recurrence nine months later. Histologically, the tumour was composed of round or polygonal atypic cells associated with spindle cell areas. In our case, the local recurrence, nuclear pleomorphism and especially the high percentage of positive cells with p53 (80%) and Ki67 (30%) antibodies support the aggressive nature of the lesion.

Epithelioid Malignant Peripheral Nerve Sheath Tumor in the Infraorbital Nerve

Epithelioid malignant peripheral nerve sheath tumors are rarely found in cranial nerves. This report describes one such tumor originating from the infraorbital nerve in a 55-year-old man who presented with diplopia and right cheek numbness. Imaging showed a mass along the floor of the right orbit, which was excised. Histology suggested melanoma or carcinoma. Immunohistochemical staining was positive for S-100 and negative for HMB-45 and cytokeratin. Four other cases from the literature involving cranial nerves are discussed.

Mucosal benign epithelioid nerve sheath tumors

Mucosal nerve sheath tumors have been well described in the gastrointestinal tract and other mucosal sites. In a series of mucosal biopsies, we have encountered a distinct subset of mucosal peripheral nerve sheath tumors characterized by small epithelioid cells and a benign clinical course. Such epithelioid nerve sheath tumors have been observed as a component of a larger study of colorectal "schwannomas," but herein we describe them in detail. A series of 7 of these lesions detected on mucosal biopsies (6 colonic, 1 bladder) was received by a single large institution in consultation material. The histologic and clinicopathologic features of the cases were reviewed. The mean age at presentation was 58.6 years with a slight female predominance (4 females, 3 males). Five of the colonic lesions were from the left colon and one from the right colon. The bladder biopsy was from the bladder neck. All of the colonic lesions were discovered as small (0.2-1.0 cm) polyps during the time of colonoscopy (3 at the time of routine screening, 2 for the workup of occult blood in the stool). The bladder neck mass was seen on bladder ultrasound after the patient presented with vaginal bleeding. None of the patients had a known history of neurofibromatosis. Histologically, the lesions showed an infiltrative growth pattern and were composed of spindled to predominantly epithelioid cells arranged in nests and whorls. The epicenters of the lesions were located in the lamina propria and extended to the superficial submucosa. The proliferating cells had uniform round to oval nuclei with frequent intranuclear pseudoinclusions and eosinophilic fibrillary cytoplasm. No mitoses were seen. All lesions expressed diffuse S-100 protein, and 3 of 5 lesions stained showed CD34 labeling in supporting cells. All were negative for CD117. All 5 lesions tested were negative for calretenin, while SM31 showed no intralesional neuraxons. One lesion was stained for epithelial membrane antigen and was negative. One lesion was associated with superficial mucosal erosion, and 1 had an inflammatory infiltrate predominantly composed of eosinophils. On follow-up of 5 patients, none has had any symptoms or recurrence of disease. Mucosal epithelioid nerve sheath tumors are a rare entity characterized by prominent epithelioid round to oval cells with an infiltrative growth pattern. These lesions are often discovered incidentally and have a benign clinical course.