Variant Of Schwannoma Research Articles

Neglected very large ancient schwannoma of the distal wrist: a case report and literature review

Ancient schwannoma is a variant of schwannoma characterized by slow progression, degenerative changes, and a higher incidence in older adults. There have been two prior reported cases of ancient schwannoma arising from the distal ulnar nerve at the wrist level, but neither were longstanding or very large. Herein, we report an ancient schwannoma found in the ulnar nerve of the distal forearm that was found to be clinically meaningful in size. A 61-year-old man presented with complaints of tingling sensation of the fourth and fifth fingers and bulging of the ulnar side of the wrist. The patient reported that the mass in his wrist had grown very slowly, starting about 10 years ago, and that he had started experiencing a tingling sensation in his fourth and fifth fingers about 3 years prior, which had become worse in the past year. Based on the results of the preoperative examination, a benign nerve sheath tumor was suspected. As it was thought that the possibility of malignancy was not high, we elected to perform a marginal excision. Pathological examination confirmed ancient schwannoma. At his most recent visit, 3 years after surgery, he reported no recurrence and that he felt better than before surgery, but some tingling sensations remained. As with small ancient schwannoma in the distal wrist, most cases of large ancient schwannoma can be treated without special complications based on an accurate preoperative diagnosis.

Ancient schwannoma in posterior triangle of neck: a rare tumor case report and literature review

Ancient Schwannoma is a rare variant of Schwannomas, a type of benign nerve sheath tumor arising from Schwann cells, hence giving it its name Schwannoma. The term ancient represents the tumor undergoing degenerative changes such as calcification, hyalinization, hemorrhage, cystic degeneration and necrosis and characteristically the loss of Antoni type A tissue. This case report describes a patient having an ancient schwannoma and the management done. Detailed management and findings starting from history and extending to USG, FNAC, CT scan, MRI and excisional biopsy have been described with positive findings supporting the diagnosis like presence of degenerative material in FNAC, peripheral enhancement on CT with the classical Target sign also visible on MRI. The following case reports helps to show how to connect the dots of different findings that may start from the patient’s basic history to eventual confirmation by biopsy.

A rare histopathological variant of Schwannoma with rosette-like arrangements and epithelioid cells: a case report from a histopathologist's perspective.

Schwannomas exhibit histopathological variation that leads to diagnostic dilemmas, although less frequent in the oral cavity. We describe a case with unique histopathology and no relevant clinical history that adds to the breadth of literature on the diversity presented by Schwannoma. A 60-year-old female patient presented with a small dome-shaped, asymptomatic swelling on the alveolar ridge 6 years in duration. Histopathologically, it showed rich cellular pathology with a unique arrangement of tumor cells forming irregular rosettes. Each rosette presented with a central core of fibrincollagenous material and the tumor cells were arranged on the periphery, exhibiting epithelioid change with evidence of mild cellular and nuclear pleomorphism. On immunohistochemical evaluation, the cells were strongly and diffusely positive for S-100 and negative for Ki-67. A diagnosis of benign Schwannoma with a rosette-like arrangement with epithelioid change was made. The case report emphasizes the risk of misdiagnosis and the importance of awareness regarding rare histopathological variants of Schwannoma.

Novel NONO::TFE3 fusion and ALK co-expression identified in a subset of cutaneous microcystic/reticular schwannoma.

Microcystic/reticular schwannoma (MRS) is a benign variant of schwannoma with a predilection for the gastrointestinal tract and skin. To date, genetic characterization of this tumor is limited. Prompted by the identification of TFE3::NONO fusion and ALK overexpression in an index case of MRS, a cohort of tumors was collected from institutional and consultation archives of two institutions. Next-generation sequencing (NGS), TFE3 fluorescence in situ hybridization (FISH), and TFE3 and ALK immunohistochemistry were performed, while clinicopathologic variables were documented. Eighteen MRS cases were identified (35 to 85 years) arising in the skin (n=8), gastrointestinal tract (n=5), adrenal gland (n=3), abdominal wall (n=1), and unknown site (n=1). Tumors showed a circumscribed to multinodular to plexiform low-power architecture with variable amounts of microcystic/reticular and solid schwannian components. Mitotic figures were scarce (0-1/10 HPFs), and atypia was absent. S100 protein and/or SOX10 immunoreactivity was noted in the microcystic/reticular and schwannian areas of all cases. NGS performed on two cutaneous tumors yielded NONO exon 12 fusion with TFE3 exon 4, and these lesions also showed HMB45 and ALK expression. Two additional cases showed ALK expression (1 weak), while a third was positive for TFE3, but these cases failed to show ALK or TFE3 rearrangement by FISH/NGS. There were no morphologic variables that correlated with the presence of NONO::TFE3. We identified a subset of microcystic/reticular schwannomas with NONO::TFE3 fusions and ALK co-expression, adding to the cohort of mesenchymal neoplasms that show ALK overexpression without rearrangement of the ALK gene.

Abrikosoff’s Tumor: A Case Repor

A 68-year-old patient had, for about 7 months, in the right buttock, a nodule of about 2 cm in diameter, rosy colour, centrally ulcerated, of hard consistency, asymptomatic. Histological examination and immunohistochemical investigations deposed for the diagnosis of granular cell tumour (Abrikosoff tumour). Granular cell tumour is a neoplasm in most cases benign, characterised by voluminous cells with eosinophilic cytoplasm and grainy appearance, with the granules corresponding to lysosomes. It is currently considered a variant of schwannoma, although cases with different histogenesis have been described. This tumour, most frequently localised on the dorsal surface of the tongue, very rarely affects the skin

Clinicopathologic Features of Neuroblastoma-like Schwannoma: A Case Report of Unusual Morphologic Variant

Neuroblastoma-like schwannoma is known as a rare unusual variant of schwannoma with difficulties of differential diagnosis with neuroblastoma, Ewing sarcoma/peripheral neuroectodermal tumor and other cutaneous small round cell tumors. Herein, we describe a neuroblastoma-like schwannoma that was presented as a painless lesion on the dorsal side of the left hand in a 39-year-old woman. Composed collagen fibers in the central core of rosettes and diffuse expression of S100 protein in the tumor cells found in the biopsy specimens confirmed the Schwann cell origin of the tumor.

Microcystic/reticular schwannoma of the lower leg: Case report with review of literature

Introduction: Microcystic/reticular schwannoma is a distinctive histopathological variant of schwannoma, which is rare. Its occurrence in the subcutaneous soft tissue of the lower extremity has rarely been reported. Case Report: We report a microcystic/reticular schwannoma arising from a subcutaneous lesion on the lower leg of a 33-year-old man. The patient noticed a subcutaneous mass on the right lower leg six months before admission and experienced radiation pain in the left lower leg. Magnetic resonance imaging revealed a well-demarcated mass with 11-mm maximum diameter with low signal intensity on T1-weighted imaging and high signal intensity on T2-weighted imaging in the subcutaneous region of the right lower leg. Histological examination revealed a cellular area at the periphery of the tumor, although the majority of the tumor showed a microcystic/reticular structure within the myxo-collagenous stroma. The current case was well capsulated and did not show an infiltrative growth pattern. In addition, aggregation of foamy macrophages was frequently seen, although it was reported as a rare feature. After complete surgical excision with clean resection margins, the patient is well, with no evidence of tumor recurrence on follow-up after postoperative 14 months. Conclusion: In this case, infrequent findings for microcystic/reticular schwannoma were observed, although the presence of the classical Antoni A area was helpful for the diagnosis of microcystic/reticular schwannoma.

A case of peripancreatic plexiform schwannoma

BackgroundPlexiform schwannoma is one of the least common variants of schwannoma, accounting for only 5% of all schwannoma cases. It generally occurs in the skin and subcutaneous tissues and is uncommon in deep soft tissue or viscera. We present an extremely rare case of plexiform schwannoma arising from the peripancreatic plexus.Case presentationA 29-year-old man presented with hyperglycemia detected during a medical checkup. He was diagnosed with type 1 diabetes based on the clinical findings and laboratory tests. During the diagnostic process for diabetes, a 2.5 cm mass was incidentally detected in the pancreas by abdominal ultrasound. Contrast-enhanced computed tomography revealed a mass that was gradually enhanced at the body and tail of the pancreas. Magnetic resonance imaging revealed low signal intensity of the mass on T1-weighted images and high signal intensity on T2-weighted and diffusion-weighted images. Magnetic resonance cholangiopancreatography showed no abnormal findings in the main pancreatic duct. Endoscopic ultrasonography (EUS) showed a lobulated, low-echoic mass with a clear boundary. EUS-guided fine needle biopsy was performed, and spindle-shaped cells that were diffusely immunopositive for S-100 and negative for c-kit and desmin were detected, resulting in a diagnosis of a neurogenic tumor arising from the pancreas or the peripancreatic nerve plexus. The patient underwent laparoscopic spleen-preserving distal pancreatectomy. Although the tumor was connected to the splenic plexus, the splenic artery could be divided along its adventitial plane. Macroscopic findings of the excised tumor consisted of multiple yellowish-white nodules, and its histopathological features were consistent with plexiform schwannoma. There was no pancreatic tissue on the dorsal surface of the tumor, which suggested that the tumor arose from the peripancreatic nerve plexus.ConclusionsThe findings documented herein can aid in the differential diagnosis of peripancreatic schwannoma and in planning appropriate treatment.

PLEXIFORM SCHWANNOMA INVOLVING THE ANTERIOR MANDIBLE

<h3>BACKGROUND</h3> Schwannomas and neurofibromas are common benign neoplasms originating from the peripheral nerves. These neoplasms originating in the oral and para-oral tissues, especially involving the jaw, are extremely rare. Plexiform schwannoma is a unique variant in which the Schwann cells demonstrate a unique plexiform pattern. A literature search revealed only 2 case reports of plexiform schwannoma involving the jaws. <h3>CASE REPORT</h3> A 47-year-old male patient was referred for consultation by his dentist for evaluation and diagnosis of a radiolucency in the anterior mandible with no apparent odontogenic/clinical etiology. The patient complained of sensitivity in this region and occasional radiating pain. Clinical examination showed no signs of infection or inflammation. The patient denied any known medical disease or history of surgeries. Cone beam computed tomography examination revealed a large, well-defined, hypodense, partially corticated lesion in the anterior mandible with evidence of impingement of the facial cortex, resulting in a scooped-out defect. The radiologic differential interpretation included peripheral ameloblastoma and peripheral giant cell granuloma. An incisional biopsy was recommended to determine the nature of this entity. Microscopic examination revealed a multicircumscribed, lobular mass bounded by a thin fibrous connective tissue capsule. Each lobule was composed of streaming fascicles of spindle-shaped cells, some of which formed a palisading arrangement. Immunohistochemistry was positive for protein S-100 and epithelial membrane antigen, which confirmed the diagnosis of plexiform schwannoma. <h3>DISCUSSION/CONCLUSIONS</h3> This is an unusual case of a unique variant of schwannoma, in this case a plexiform type, which is an extremely rare neurogenic neoplasm. This atypical presentation and location of the lesion, which mimics other peripheral benign neoplasms, highlights the importance of a systematic workup with the aid of the appropriate diagnostic tools for ideal patient care. It demonstrates the important role of immunohistochemistry to confirm the nature of this entity.

Cutaneous Ancient Schwannoma of the Ear

Schwannoma is a benign encapsulated nerve sheath tumor composed of Schwann cells, that may arise anywhere along the course of a nerve. Cutaneous schwannomas, associated with peripheral nerves, usually present as a slow-growing well-circumscribed nodule, localized in the dermis or subcutaneous tissue. They are generally asymptomatic; however, they may become painful by the nervous compression. Since the clinical signs are non-specific, histology is required for a definitive diagnosis. Herein, we present a case of a solitary cutaneous ancient schwannoma of the ear, a histopathological variant of schwannoma with distinctive morphological characteristics.

Microcystic reticular schwannoma in the lumbar spine

Microcystic/Reticular Schwannoma [MRS] is a rare histological variant of Schwannoma which has been reported to mainly affect the gastrointestinal tract. Few cases involving soft tissue and various visceral and salivary glands have also been reported. However, MRS involving the spine is extremely rare with only two cases reported till date. Hereby, we present a case of Microcystic/Reticular schwannoma in a middle aged female who presented with complaints of pain and numbness in both legs. MRI findings were suggestive of an intradural extramedullary neoplasm. Diagnosis of MRS was made based on the typical histopathological features and Immunohistochemical positivity for S100. MRS is a variant of Schwannoma, which differs from the conventional Schwannoma in several aspects. Raising awareness regarding this variant is essential to the budding pathologists to prevent their misdiagnosis. Keywords: Nerve sheath tumors, Benign neural neoplasms, Myxoid neural masses, Spinal schwannomas.

Giant intradural plexiform schwannoma of the lumbosacral spine - a case report and literature review

BackgroundPlexiform schwannoma (PS), variant of schwannoma, often involves multiple fascicles as plexiform neurofibroma, and is usually located superficially on the dermis and subcutaneous layers. Spinal PS is extremely rare, and there is insufficient information on its natural course and treatment strategy. We describe the clinical features and treatment of giant intradural PS at the lumbosacral spine.Case presentationA 66-year-old man presented with leg pain, paresthesia, and weakness for 2 years. Magnetic resonance imaging demonstrated a large mass lesion involving a continuous multi-lobulated bead-like mass and a cystic portion from L1 to S3. The lesion was iso-intense on T2-weighted images (WI), iso- to slightly low-intense on T1-WI, and heterogeneous enhancement on contrast-enhanced T1-WI. The large mass lesion had three portions, including a cystic mass at L1, continuous multi-lobulated bead-like mass with a cystic portion from L2 to S1, and multi-lobulated mass from S2 to S3, which were identified with severe adhesions with cauda equina on operative assessment. Grossly total extirpation was achieved at the lumbar spine, and remained three round shaped small masses at the lumbar area and a multi-lobulated round masses from S2 to S3 involving nerves related with motor function of the lower extremities and anal sphincter, respectively. Histological examination revealed multinodular or plexiform growth pattern composed of spindle-shaped tumor cells, which were diffusely and strongly positive for S100 protein with KI67 < 1%. There were no recurrence of preoperative symptoms and changes of the remained masses over a 2-year follow-up period.ConclusionSubtotal extirpation to minimize neural deficits and close observation can be considered an appropriate treatment strategy for a giant spinal PS considering its benign prognosis and histological features, with a high risk of neurological damage during surgery.

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

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

Schwannoma neck: a diagnostic dilemma

&lt;p&gt;Schwannomas are less common benign slow growing tumors originating from Schwann cells. In the head and neck region, schwannomas arise most commonly from the vagus nerve or the sympathetic chain. We present this case as the location of schwannoma is extremely rare and due to the diagnostic difficulties it posed. A 48 year old male presented with right neck swelling and breathing difficulty to our OPD. Patient underwent ultrasonogram of neck, MRI neck and Fine needle aspiration cytology (FNAC) of the lesion. Each of the investigations suggested different pathology which made the diagnosis challenging. During surgery, the lesion was found to arise from right recurrent laryngeal nerve. After excision of the lesion, the patient developed hoarse voice and the pathological examination revealed schwannoma. Schwannomas that originate from Schwann cells can affect any part of the body. MRI, CT, USG and FNAC have been suggested in the literature for diagnosing the lesion. Trucut biopsy should be considered in situations where FNAC becomes inconclusive. Surgical excision is the treatment of choice. Histologically, five variants of schwannomas have been described in the literature namely common, plexiform, cellular, epithelioid and ancient schwannoma. To conclude, schwannoma arising from RLN which masqueraded as a thyroid swelling is a rare entity. The diagnostic modalities suggested in the literature were unable to pin point the diagnosis. Once, FNAC shows an inadequate specimen, a trucut biopsy should be considered as the next investigation modality.&lt;/p&gt;

Adrenal Microcystic Reticular Schwannoma

Schwannomas are usually benign tumors, originating from the Schwann cell myelin sheath around the peripheral or cranial nerves. Visceral schwannomas are rare, and less than 60 cases of adrenal schwannomas have been reported. Microcystic/reticular schwannoma (MRS) is the rarest variant of schwannoma and only 2 cases have been reported in the adrenal gland. Here we describe a third case. We describe a case of an adrenal MRS with a comprehensive literature review. The patient was a 69-year-old, Caucasian female with abdominal pain. An abdominal computed tomography scan revealed a solid, lobulated, 78-mm mass of the left adrenal gland. Two inconclusive adrenal biopsies were performed and then she was referred to our tertiary center for further evaluation. No clinical or laboratorial signs of endocrine dysfunction were identified. A positron emission tomography scan with fluorodeoxyglucose showed a single left adrenal hypermetabolic mass (SUVmax = 71.7), suggestive of malignancy. In this context, an open left adrenalectomy was undertaken. The histologic evaluation showed an MRS. Adrenal MRSs are extremely rare tumors. Definitive diagnosis of schwannoma can only be made by surgical excision with histopathologic and immunohistochemical evaluation of the specimen.

PLEXIFORM SCHWANNOMA OF THE ORAL/PHARYNGEAL REGION: REPORT OF FOUR CASES AND A REVIEW OF THE LITERATURE

Plexiform schwannoma represents an unusual schwannoma variant, characterized by multinodular growth grossly and/or microscopically. A review of the English language literature reveals only 30 previously reported cases involving the oral/pharyngeal region, and herein we present 4 additional cases. Among these 34 cases, the average age at diagnosis was 27 years (range 5 to 58 years), with a female-to-male ratio of 1.3:1. The most frequently involved sites were the lips (n=11) and tongue (n=11). Lesion duration prior to presentation was reported in 15 cases and ranged from 6 weeks to 26 years. The average lesion size was 2.1 cm (range 0.4 to 8.5 cm). Three tumors were described as “large” or “giant,” including one extending from the sublingual region to the mediastinum. The typical clinical presentation was a solitary/localized, painless, and slowly enlarging swelling. However, 5 patients exhibited other clinical findings (e.g., pain/discomfort, sore throat, dysphagia, dyspnea). Three cases arose in association with neurofibromatosis 2 (NF2). Other neural tumor types (e.g., conventional schwannoma, meningioma) and/or >1 plexiform schwannoma were found in 5 patients (3 with NF2 and 2 who did not fulfill diagnostic criteria for NF2). Microscopic examination typically showed a proliferation of multiple well-circumscribed tumor nodules, each surrounded by a thin capsule. Antoni A and B patterns were evident in varying proportions. Infrequent histopathologic findings included ancient change (n=1) and induction of adjacent surface epithelium/odontogenic epithelial rests (n=1). Immunohistochemical findings included reactivity for S-100 protein among the tumor cells (15/15 cases), reactivity for EMA among capsular perineural cells (3/4 cases), and no reactivity for NFP among the tumor cells (6/6 cases). Most patients (n=22) were treated by excision or enucleation. Among the 14 cases for which follow-up information was provided, 3 recurred. Unlike plexiform neurofibromas, plexiform schwannomas exhibit only a weak association with neurofibromatosis and have no known malignant potential.

Ancient Schwannoma: A Rare Intramural Intra-lingual Lesion.

Ancient schwannoma is an uncommon schwannoma variant which is a benign tumour of Schwann cell origin. It is relatively a rare tumour (25%) in the head and neck region. It is encapsulated and well demarcated from the surrounding tissues. A 35years old patient in this case presented with painless swelling of the tongue. Trans-oral excision of the intramural lesion was performed. Histopathological and immuno-histochemistry confirmed the diagnosis of schwannoma. This case is of interest on account of the complexity of its diagnosis and the atypical site, that is, intra-mural, of appearance of a schwannoma.

Epithelioid schwannoma with diffuse nuclear pseudoinclusions: a rare variant of schwannoma

Epithelioid schwannoma with diffuse nuclear pseudoinclusions: a rare variant of schwannoma

Microcystic/reticular schwannoma of the adrenal gland: a case report and literature review

Microcystic/reticular schwannoma is a recently described, rare, distinctive histological variant of schwannoma with a predilection for the gastrointestinal tract [1]. Unlike classic Schwannoma, most microcystic/reticular Schwannoma had an incomplete fibrous capsule, two distinctly different areas - hypercellular areas and myxoid areas, Microcystic/reticular schwannoma occurs in the internal organs, especially in the digestive tract and a rare case occurs in the adrenal glands [1–3]. Herein, we report a case of microcystic/reticular schwannoma of the adrenal gland, in a 60-year-old male with 7.0 cm × 6.0 cm × 5 cm mass in the left adrenal gland. The tumor showed a vague multinodular appearance with a pushing border and arranged in a microcystic and reticular growth pattern with anastomosing and intersecting strands of spindle cells in a myxoid or collagenous/hyalinized stroma. Tumor cells showed diffuse nuclear and cytoplasmic positivity for S-100.

SMARCB1/INI1 Loss in Epithelioid Schwannoma

The epithelioid variant of schwannoma is rare, and loss of SMARCB1/INI1 expression has been observed in a subset of cases. Our aim was to further define the clinicopathologic features and to evaluate SMARCB1/INI1 deficiency in a large cohort of 65 epithelioid schwannomas diagnosed between 2002 and 2015, which consisted of 32 men and 33 women with median age at diagnosis of 45 years (range, 13 to 75 y). Most tumors arose in the extremities (upper, 20, lower, 15) and trunk (17); 9 were visceral (8 gastrointestinal). Most somatic tumors were in dermis/subcutis (53/54) and encapsulated (53/54) with an epithelial membrane antigen-positive perineurial capsule in 46 cases; visceral tumors were unencapsulated. No patients were reported to have any neurocristopathy. Three patients had multiple lesions (2 each). Tumor size range was 0.4 to 22.7 cm (median, 1.2 cm). Tumors showed multilobulated growth of uniform epithelioid cells in sheets and nests or singly dispersed within a frequently myxoid or hyalinized stroma. Tumor cells had round vesicular nuclei and abundant palely eosinophilic cytoplasm, usually lacking significant pleomorphism or hyperchromasia. Some tumors showed foci resembling conventional schwannoma (spindled morphology, 29; Antoni B foci or Verocay bodies, 8; hyalinized thick-walled vessels, 16). Mitoses ranged from 0 to 9 per 10 high-power fields (median count, 1). No tumor had necrosis. Twenty-three cases showed degenerative nuclear atypia. Focally striking cytologic atypia was present in 7 tumors, 3 of which showed transformation to epithelioid malignant peripheral nerve sheath tumor. All tumors showed diffuse positivity for S-100 protein and consistent positivity for SOX10 (50/50), while INI1 expression was lost in 24 of 57. Other positive immunohistochemical results were: glial fibrillary acidic protein (15/37) and focal keratin (2/40); epithelial membrane antigen (0/53) and melanocytic markers were negative (Mart-1 0/29; HMB-45 0/23). Most patients underwent local excision (13 complete; 47 marginal/positive margins). Follow-up data available for 31 patients (range, 1 to 108 mo; median, 37) indicated that no patient had developed metastatic disease, including 3 cases with cytologic atypia, one of which showed malignant transformation. One tumor without atypia developed local recurrence 48 months after marginal excision; all other patients were alive with no evidence of disease. Epithelioid schwannoma most commonly occurs as a superficial tumor on the extremities or trunk in adults. Loss of SMARCB1/INI1 expression is seen in 42% of tumors. Tumors follow a generally benign clinical course, although recurrence and malignant transformation are infrequent. Some tumors are characterized by notable cytologic atypia, the significance of which is uncertain but which may indicate a morphologic continuum with low-grade epithelioid malignant peripheral nerve sheath tumor.