Benign epithelioid schwannoma

Glandular Schwannoma With Apocrine Decapitation Secretion: A True Divergent Differentiation or Entrapped Normal Tissue?

ABSTRACT

We report an unusual case of schwannoma with glandular elements that demonstrated apocrine decapitation secretion. The glandular structures were embedded within the tumor, varied in shape and size, and were lined by a double-to-multilayered epithelium, with the inner layer composed of monomorphous cuboidal to columnar cells, focally with apocrine decapitation secretion, and the outer layer representing myoepithelial cells. A normal eccrine unit was observed near the lesion. Immunohistochemical studies showed that all luminal cells of the glandular structures stained positive for CK7, whereas myoepithelial cells expressed S100 and p63, and epithelial membrane antigen highlighted the luminal border. CK20 and neuroendocrine markers were negative in the glandular elements.Our findings suggest that the origin of the glandular elements in our case was represented by entrapped glands. Two theories may explain the epithelial hyperplasia observed in the present case as follows: the obstructive effect theory and the inductive ability of a mesenchymal proliferation to produce epidermal or adnexal changes. We suggest that, in a subset of cases, the origin of the glandular elements might represent entrapped glands, wherein their histomorphology/cytomorphology recapitulates the elements comprising the normal adjacent tissue. Further research is necessary to elucidate the histogenesis of glandular schwannoma.

Rare cases of colonic schwannomas

Schwannomas of the gastrointestinal tract are rare spindle cell tumors that account for 2-6% of mesenchymal tumors. An elderly male was found to have a left colon mass on CT scan and colonoscopy with pathology of fibrotic tissue. A laparoscopic-assisted left hemi-colectomy with primary anastomosis was performed. Pathology demonstrated spindle cell neoplasm arranged in short fascicles that were strongly and diffusely positive for S100. An elderly female was found to have a submucosal lesion on surveillance colonoscopy in the proximal transverse colon. Biopsy with jumbo forceps revealed spindle cell neoplasm positive for S100. Patient underwent an uncomplicated limited non-oncologic segmental transverse colectomy. We report only the ninth case of left and sixth in the transverse colon described in the literature. As is true for other mesenchymal tumors, mucosal biopsy is usually inconclusive and deep biopsy or submucosal resection is required, making pre-operative surgical decision difficult.

Mesenchymal tumours with melanocytic expression: a potential pitfall in the differential diagnosis of malignant melanoma

Mesenchymal tumours with melanocytic expression can pose a diagnostic challenge because they frequently demonstrate both morphological and immunohistochemical overlap with other cutaneous melanocytic neoplasms. Therefore, they present potential pathological pitfalls that may lead to a misdiagnosis of malignant melanoma. Mesenchymal neoplasms that closely mimic melanoma include malignant melanotic nerve sheath tumour (melanotic schwannoma), epithelioid schwannoma, malignant peripheral nerve sheath, cutaneous syncytial myoepithelioma, clear cell sarcoma of soft tissue, and perivascular epithelioid cell tumour. Awareness of these melanoma mimics is necessary for establishing the correct diagnosis so that the appropriate clinical management can be rendered to the patient. This in-depth review highlights key diagnostic features and molecular genetics and also discusses the differential diagnosis and treatment of mesenchymal tumours that exhibit melanocytic expression.

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.

Epithelioid Cutaneous Mesenchymal Neoplasms: A Practical Diagnostic Approach

Epithelioid cells are rounded or polygonal cells with abundant eosinophilic or clear cytoplasm and ovoid to round nuclei, superficially resembling epithelial cells. Cutaneous mesenchymal neoplasms composed predominantly or exclusively of epithelioid cells are relatively uncommon and can cause considerable diagnostic difficulties due to overlapping histologic features among heterogeneous groups of tumors. Familiarity with practical diagnostic approaches and recognition of key histopathologic features are important for correct diagnosis and management. This review summarizes the histologic features of epithelioid cutaneous mesenchymal neoplasms and discusses their differential diagnoses from malignant melanomas and carcinomas.

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.

Primary adrenal schwannoma: a series of 31 cases emphasizing their clinicopathologic features and favorable prognosis

PURPOSE

Primary adrenal schwannoma (PAS) is a very rare benign tumor, and most of them have been described in case reports. This study aimed to analyze their distinct clinicopathologic features and follow-up data through the largest series yet.

METHODS

Clinicopathologic features of 31 primary adrenal schwannomas were retrospectively studied. Imaging and histologic features were re-evaluated and summarized. Immunohistochemical markers were measured, including S100, SOX10, AE1/AE3, EMA, SMA, Desmin, HMB45, GLUT1, and Ki67. Follow-up of all cases was performed.

RESULTS

All the tumors were clinically misdiagnosed as nonfunctioning adrenal adenoma (NAA; 23/31), aldosterone-producing adenoma/aldosteronoma (APA; 3/31), cortisol-producing adenoma (CPA; 3/31), or pheochromocytoma (PCC; 2/31). Some 87% (27/31) presented with adrenal incidentaloma, and 13% (4/31) had a clinical symptom or unregulated hormone levels. They comprised conventional (19/31), cellular (7/31), plexiform (2/31), ancient (1/31), epithelioid (1/31) and microcystic/reticular variants (1/31) and had various histologic features. Immunohistochemically, all tumors (31/31) were positive for S100 and Sox10, with a low Ki-67 proliferative index. In the long-term follow-up (mean, 53 mo.; median, 56 mo.), none had evidence of recurrence and metastasis. Univariate analysis showed that OS and DFS were not associated with age; sex; tumor side, size, or number; adrenal-related symptoms; gross feature (solid vs. cystic); or any histologic feature (P > 0.9999).

CONCLUSION

PAS is an extremely rare tumor and mostly appears as an incidentaloma. Clinically, it tends to be misdiagnosed as other common adrenal tumors. This tumor has a benign biologic behavior and prognosis, without correlations with clinical or histologic parameters.

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.

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.

Malignant renal schwannoma in a cat

A nine-year-old male European shorthair cat with rapidly enlarging mass at the left kidney doubted to be malignant was presented. The purpose of this study is to present the clinical, radiological and pathological findings of a primary renal tumor in the cat. Grossly, the mass mostly encapsulated the kidney. Histologically, excisional biopsy showed worrying histological features. A sarcoma-like tumor composed mainly of neoplastic spindle-shaped cells. Neoplastic nodules of aggregations of fusiform cells arranged in multidirectional bundles. Immunohistochemically, several immunohistochemical satins (melan-A, S-100, vimentin, actin, desmin, cytokeratin, neurofilament, melan-A, NSE, synaptophysin, chromogranin, Glial Fibrillary Acidic Protein GFAP, Collagen IV and CD99) were used to differentially diagnose the mass. The stained neoplastic sections positively tested to S-100, but negative to the other aforementioned immunohistochemical stains. Immunohistochemistry with S-100 antibody staining showed an unusually strong positive reaction throughout the tumor cells. Based on our comparative diagnosis relative to other tumors, in addition to the progressive clinical signs, histopathological and immunohistochemical results, this case was presumptively diagnosis as a malignant schwannoma. According to our investigation of the relevant literature, this study of malignant renal Schwannoma (malignant peripheral nerve sheath tumor) is a highly rare case not previously characterized in a cat.

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.

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.

Microcystic/Reticular Schwannoma Arising in the Submandibular Gland: A Rare Benign Entity that Mimics More Common Salivary Gland Carcinomas

Microcystic/reticular schwannoma is a recently described variant of schwannoma with a predilection for the gastrointestinal tract, rarely involving the head/neck region. This is the first reported case involving the submandibular gland. We present a case in a 34 year old man with 4.5 cm submandibular mass. Fine needle aspiration suggested a spindle cell lesion. Frozen section evaluation raised the possibility of mucoepidermoid carcinoma. Resection showed a well circumscribed mass with a mucoid appearance. Histologic findings include a lobular architecture with fibrous septa, a lympho-plasmacytic infiltrate, and scattered lymphoid aggregates at the periphery. There are two distinct histologic patterns with solid areas of spindle cells and areas of spindle/ovoid cells with a microcystic pattern in a myxoid background. The tumor has a pushing border, with extension into adipose and adjacent parenchyma, without cytologic atypia or necrosis. Immunohistochemical stains are positive for S-100 and CD34, and negative for calponin, mammoglobin, ALK1, p63, ER, GFAP, SMA, desmin, cytokeratin 7, cytokeratin AE1/AE3, and C-Kit. Mucicarmine stain is negative. Recognition of this benign unusual variant of schwannoma is paramount for appropriate conservative treatment due to the morphologic and immunohistochemical overlap with primary salivary gland carcinomas.

Microcystic/Reticular Schwannoma of the Mandible First Case Report and Review of the Literature

Schwannoma comprises a group of nerve sheath tumors. Morphologic variants of schwannoma have no distinct relationship to clinical behavior, but unawareness of rare variants may lead to diagnostic pitfall and risk of mistreatment. Microcystic/reticular schwannoma is a recently described rare variant of schwannoma. We report a case of a 61-year-old female with a 5.0 cm × 3.5 cm × 3.0 cm mass in the right mandible, which has never been reported to date. Light microscopic evaluation showed that the mass was circumscribed with focal infiltration. Arranged in a prominent microcystic and reticular growth pattern, tumor cells were spindle-shaped with eosinophilic cytoplasm. No evidence of cytologic atypia, mitosis, or necrosis was observed. The stroma of the tumor mainly contained myxoid material with local infiltration of hyalinized collagen. Tumor cells showed diffuse and strong nuclear and cytoplasmic immunoreactivity for S100 protein. Tumor cells were also positive for CD34, CD99, and NSE, but negative for CK, EMA, CK5/6, P63, Calponin, CD10, SMA, Desmin, GFAP, NF, Syn, and CgA. The proliferation marker MIB-1 showed <1% nuclear reaction. Furthermore, we reviewed the clinical and pathological features of 24 previously reported cases of microcystic/reticular schwannoma. Unlike classic schwannoma, the reticular variant showed striking microcystic and reticular architecture microscopically. Recognition of these distinct entities is essential in avoiding misdiagnosis. Unlike classic schwannoma with a complete capsule, some masses were reported to lack encapsulation or contain focal infiltration. Further follow-up of tentative or identified cases is necessary to better understand this schwannoma.

Cutaneous microcystic/reticular schwannoma: a poorly recognized entity

BACKGROUND

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

AIMS

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

RESULTS

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

CONCLUSION

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

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.

Malignant epithelioid schwannoma of the oral cavity in a cat

A malignant epithelioid schwannoma of the oral cavity was diagnosed in an 8-year-old domestic short-hair cat. The mass was located in the gingiva of the upper left premolar to molar region and showed multinodular growth patterns. The mass comprised epithelioid cells arranged in densely packed sheets. Tumor cells had large, round to oval nuclei with prominent nucleoli and an abundant eosinophilic cytoplasm. Immunohistochemically, most of the tumor cells were positive for S-100 protein, glial fibrillary acidic protein and vimentin, but all lacked melanoma-associated antigen and muscle and neuroendocrine markers. Stains for type IV collagen showed linear immunoreactivity around single cells and groups of cells. Ultrastructurally, tumor cells were separated by a well-defined basement membrane, and interdigitating cell processes were observed. To our knowledge, this is the first report of feline malignant epithelioid schwannoma.

Schwannomas and their pathogenesis

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

Bowel mesentery (meso-appendix) microcystic/reticular schwannoma: Case report and literature review

Microcystic/reticular schwannoma is a recently described variant of schwannoma with a predilection for the gastrointestinal tract. Due to overlapping features with other tumors, unawareness of this tumor type may lead to diagnostic and therapeutic pitfalls. We here report a case of microcystic/reticular schwannoma arising in the meso-appendix of a 43-year-old woman. The tumor was incidentally discovered by computed tomography scan for unrelated reasons. A laparoscopic operation was performed shortly after admission. Histological examination revealed a circumscribed tumor with a striking microcystic and cribriform architecture. Immunohistochemically, the tumor cells were diffusely positive for S100 protein, glial fibrillary acid protein and protein gene product 9.5, which were consistent with a peripheral nerve sheath tumor. The patient remains well with no signs of recurrence at a 10-mo follow-up. To our knowledge, this is the first case of microcystic/reticular schwannoma arising in the meso-appendix. Albeit very rare, microcystic/reticular schwannoma should be included in the differential diagnosis of appendiceal tumors.

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.

Clinical, radiological, and pathological features of 26 intracranial and intraspinal malignant peripheral nerve sheath tumors

Object

Intracranial and intraspinal malignant peripheral nerve sheath tumors (MPNSTs) are rarely reported because of their extremely low incidence. Knowledge about these tumors is poor. In this study the authors aimed to analyze the incidence and clinical, radiological, and pathological features of intracranial and intraspinal MPNSTs.

Methods

Among 4000 cases of intracranial and intraspinal PNSTs surgically treated between 2004 and 2011 at Beijing Tiantan Hospital, cases of MPNST were chosen for analysis and were retrospectively reviewed. To determine which parameters were associated with longer progression-free survival (PFS) and overall survival (OS), statistical analysis was performed.

Results

Malignant PNSTs accounted for 0.65% of the entire series of intracranial and intraspinal PNSTs. Twenty-four (92.3%) of these 26 MPNSTs were primary. Radiologically, 26.9% (7 of 26) of the MPNSTs were misdiagnosed as nonschwannoma diseases. Twenty-one patients were followed up for 1.5 to 102 months after surgery. Twelve patients experienced tumor recurrence, and median PFS was 15.0 months. The 2- and 3-year PFS rates were 47.7% and 32.7%, respectively. Five patients died of tumor recurrence, and median OS was not available. The 2- and 3-year OS rates were 74.7% and 64.0%, respectively. Univariate analysis revealed that female sex, total tumor removal, and primary MPNSTs were significantly associated with a better prognosis. Multivariate analysis revealed that only total removal was an independent prognostic factor for both PFS and OS.

Conclusions

Malignant PNST within the skull or spinal canal is a rare neoplasm and is seldom caused by benign schwannomas. Radiologically, intracranial or intraspinal MPNST should be differentiated from meningioma, chordoma, fibrous dysplasia of bone, and ear cancer. Total resection whenever possible is necessary for the prolonged survival of patients, especially males.

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

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

Neurogenic tumors of soft tissue

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

Retroperitoneal schwannoma is characterized by a high incidence of cellular type and GFAP-immunoreactivity

To clarify the clinicopathologic characteristics of retroperitoneal schwannomas, which are sometimes confused with other spindle cell tumors, 27 cases were studied microscopically and immunohistochemically. The 27 cases consisted of 17 females and 10 males, the ages of whom ranged from 31-79 (mean 57.4) years. Gross examination revealed well-demarcated, encapsulated tumors, 3-15 cm (mean 8 cm) in diameter. Microscopic review divided them into 13 cases of cellular/fascicular, 3 of conventional, 6 of intermediate, and 5 of ancient type. Cellular/fascicular schwannomas were composed of cellular fascicles of spindle cells, in which nuclear palisading, Antoni B area and cyst were unclear, while numerous foamy cells were intermingled. Immunohistochemical investigation revealed diffuse, strong positivity for S-100 protein and Sox10 in all tumors studied. In addition, glial fibrillary acidic protein (GFAP) was extensively expressed in 92% of the cellular/fascicular type, while it was less prominent in others. The present study suggests that retroperitoneal schwannoma often occurs in the middle-aged woman, grows to a large size, exhibits cellular/fascicular microscopic features in half of the cases, and may arise from GFAP-positive Schwann cells. The presence of hyalinized vessels and dense infiltration of foamy macrophages as well as diffuse immunoreactivity for S-100 protein and Sox10 are helpful for the differential 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.

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.

Diagnosis and management of intracranial malignant peripheral nerve sheath tumors

OBJECTIVE

Intracranial malignant peripheral nerve sheath tumors (MPNSTs) are rare and generally carry a poor prognosis. We have analyzed our experience with MPNSTs and conducted a review of the literature in an attempt to identify a rational approach to the management of these tumors.

METHODS

Eight patients underwent surgical treatment for intracranial MPNSTs during a 10-year period from 1996 to 2005. The general strategy was to perform complete resection whenever possible and to provide adjuvant radiotherapy for residual tumor. Chemotherapy was not used in this group. The clinical, radiological, operative, and pathological findings of the patients were reviewed retrospectively.

RESULTS

Six of the eight patients underwent primary operations; two of the eight patients had previously undergone other transcranial surgery operations. Total tumor resection was achieved in five patients. At this time, two have been recurrence-free for 3.5 and 5 years, respectively, and the other three patients had a mean postoperative survival of 7 months. There was one case of near total (>90%) and two cases of partial (<90%) tumor removal; the postoperative survival rate was 4, 4, and 2 months, respectively. Only two patients in our group accepted radiotherapy after surgery; one survived only 4 months and the other has been recurrence-free for 5 years.

CONCLUSION

MPNSTs are fast-growing, invasive tumors with rather unsatisfactory outcomes. Total surgical resection seems to be the most effective therapeutic method, and radiotherapy may play a role in local control.

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.

[Gastrointestinal stromal tumors--microscopic and immunihistochemical features]

BACKGROUND/AIM

Gastrointestinal (GI) stromal tumors (GIST) are the most common mesenchymal tumors of GI tract. The most frequent localization is gastric (60-70%) followed by intestinal localization (20-30%). The histogenesis, classification, diagnostic criteria and biological behavior of GIST are still discussable. Gastrointestinal stromal tumors are thought to originate from interstitial pacemaker intestinal cells of Cajal. Histologic appearance of a GIST is complicated and biologic potential unpredictable. The aim of of tha study was to investigate anatomic localization, the size of the tumor, incapsulation, microscopic and immunohistochemical characteristics.

METHODS

The study involved 21 GIST taken by a complete resection in the period from 1994-2006. The analysed parameters were the localization, size, microscopic (mitotic index, nectosis, bleeding, invasivity) and immunohistochemical characteristics (CD117 (c-kit), CD34, desmin, vimentin, smooth muscle actin and s-100 protein expression.

RESULTS

Gastrointestinal stromal tumors (n=21) size varied from 10-150 mm were most frequently gastric localised with predominance of malignant tumors (85.72%). Most GIST were comprised of a uniform spindle cell population, but some were dominated by epitheloid cells. Eosinophilic cells stained CD117, CD34 and vimentin positively, were usually arranged in fascicles with the presence of skeinoid fibers. Positive correlation of biologic potential and tumor size, haemorrhagia and mitotic index were found, so as negative correlation of biologic potential and incapsulation.

CONCLUSION

The above results, a specially localization, tumor size, mitotic index, CD117, CD34 and vimentin positivity, may be helpful for setting of a widespread criteria for diagnostic and differential diagnosis of GIST and their use in practice and therapy.

Signet ring cell gastric schwannoma: report of a new distinctive morphological variant

An 89-year-old woman was seen for indigestion, light chest pain, and melanotic stools. Endoscopic examination revealed 2 submucosal gastric masses. A subtotal gastrectomy showed 2 submucosal masses in the stomach: one infiltrating through the muscularis propria into the serosa, the second one, a well-circumscribed submucosal nodule. Histologic examination showed large tumor cells infiltrating diffusely through the muscularis propria into the subserosa. On higher magnification, numerous signet ring cells were present against a myxoid stroma, in addition to large vacuolated epithelioid cells. There was no evidence of invasion, necrosis, nuclear pleomorphism, or mitotic activity. Initial diagnostic considerations based on the histology included signet ring cell carcinoma, malignant melanoma, and a myxoid mesenchymal tumor, including gastrointestinal stromal tumor. A panel of immunohistochemical stains showed diffuse strong positivity for S-100 protein and negative reaction for CD117, bcl-2, cytokeratin AE1/AE3, Melan-A, HMB45, smooth muscle antigen, and other differentiation markers. Electron microscopic examination revealed elongated, complex, and interdigitating cell processes covered by a thin layer of continuous basement membrane material characteristic of peripheral nerve sheath differentiation. The presentation of this tumor was significant in that it was multifocal and infiltrative, mimicking a malignant neoplasm. The extensive myxoid/signet ring cell change represents a heretofore-unreported histologic variant of gastric schwannoma.

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.

Rosetoid schwannoma (neuroblastoma-like) in association with an anetoderma

BACKGROUND

We report an additional case of an extremely uncommon but distinctive histological variant of benign schwannoma, which was previously designated as neuroblastoma-like schwannoma by Goldblum et al.

METHODS

A 29-year-old woman referred to a 6-year-history of an atrofic macule. Its clinical appearance was similar to that of an anetoderma.

RESULTS

A cutaneous biopsy showed findings consistent with a neuroblastoma-like schwannoma with the following peculiar features: (i) Being fully composed of rosette-like structures. (ii) Association to an anetoderma.

CONCLUSIONS

Because neither the histological pattern nor the type of tumor allows a differential diagnosis with neuroblastoma, we propose the descriptive term of rosetoid schwannoma. And to our knowledge, this will be the first case reported of rosetoid schwannoma associated to anetoderma.

Malignant epithelioid cranial nerve sheath tumor: case report of a radiation response

Malignant epithelioid nerve sheath tumors (MESs) especially those involving intracranial cranial nerves are rare and thought to be radioresistant. We report a case of a MES involving the Vth and VIIth cranial nerves responsive to radiotherapy. A 41-year-old man with progressive left facial weakness underwent an MRI that disclosed an enhancing lesion involving both V3 cranial nerve and the distal VIIth nerve. Biopsy confirmed a malignant epithelioid schwannoma. The tumor was resected but residual tumor was present at the cut end of the infraorbital nerve, within the oral cavity and at the brainstem. Positive excision margins were irradiated to 60 Gy/30 fractions by a wedge pair technique extending from the inferior orbit to C2. Tumor was controlled for 38 months and then radiographic recurrence was resected from the infratemporal fossa outside the irradiated field.A new primary MES tumor developed at 69 months at the C1/C2 root levels at the lower edge of the previously irradiated field. It was subtotally resected but by 77 months residual tumor had grown inferiorly down to C5 so this area was re-irradiated with a complicated 7-field approach to spare spinal cord. Initially the tumor responded but ultimately progressed posteriorly where radiation dose was limited by spinal cord tolerance. New involvement of the Xth cranial nerve was noted. The patient expired from brainstem compression 7 years after initial radiotherapy. The long-term control of the original tumor despite positive margins argues for the use of radiotherapy in the treatment of these tumors.