Electron microscopy in the diagnosis of malignant schwannomas. A report of six cases

A Rare Case of Malignant Peripheral Nerve Sheath Tumor of Larynx

Malignant peripheral nerve sheath tumors are highly aggressive tumors and they arise either de novo or from preexisting benign schwannoma or neurofibromatosis. Malignant peripheral nerve sheath tumor of the larynx is an extremely rare neoplasm, for which accurate diagnosis is difficult and the therapy is usually delayed. Although wide surgical excision is the mainstay of treatment, radiation therapy also plays an important role in the control and treatment of locally recurrent disease and non resectable cases. Here we are reporting a case of malignant peripheral nerve sheath tumor of the larynx without definite evidences of von Recklinghausen's disease or preexisting benign peripheral nerve sheath tumor.

Malignant peripheral nerve sheath tumor presenting as orbito temporal lump: Case report and review of literature

Malignant peripheral nerve sheath tumor (MPNST) is a rare soft tissue sarcoma. The most common anatomical sites include the upper and lower extremities and trunk and less commonly the head and neck. To our knowledge, few patients with a cranial or facial MPNST have been reported. We report such a lesion in a 35-year-old woman who presented with left sided rapidly progressive proptosis and visual loss due to an orbital lump extending up to the temporal lobe. Cranial imaging showed a huge mass invading the orbital wall and temporal bone. The presumptive diagnosis was a malignant orbital tumor. Preoperative fine needle aspiration cytology of the orbital mass came to be neurofibroma. Near total resection of the tumor was done. Histopathology revealed MPNST which was subsequently confirmed on the basis of immunopositivity for S-100. The patient recovered uneventfully and was discharged 8 days after surgery with an advice to attend cancer institute for possible radiotherapy.

Primary malignant peripheral nerve sheath tumor at unusual location

Malignant peripheral nerve sheath tumor (MPNST) is a rare soft tissue sarcoma. Most arise in association with major nerve trunks. Their most common anatomical sites are the proximal portions of the upper and lower extremities and the trunk. MPNSTs have rarely been reported in literature to occur in other unusual body parts. We review all such cases reported till now in terms of site of origin, surgical treatment, adjuvant therapy and outcome and shortly describe our experience with two of these cases. Both of our case presented with lump at unusual sites resembling neurofibroma, one at orbitotemporal area and other in the paraspinal region with characteristic feature of neurofibroma with the exception that both had very short history of progression. They underwent gross total removal of the tumor with adjuvant radiotherapy postoperatively. At 6-month follow-up both are doing well with no evidence of recurrence.

Use of electron microscopy to classify canine perivascular wall tumors

The histologic classification of canine perivascular wall tumors (PWTs) is controversial. Many PWTs are still classified as hemangiopericytomas (HEPs), and the distinction from peripheral nerve sheath tumors (PNSTs) is still under debate. A recent histologic classification of canine soft tissue sarcomas included most histologic types of PWT but omitted those that were termed undifferentiated. Twelve cases of undifferentiated canine PWTs were evaluated by transmission electron microscopy. The ultrastructural findings supported a perivascular wall origin for all cases with 4 categories of differentiation: myopericytic (n = 4), myofibroblastic (n = 1), fibroblastic (n = 2), and undifferentiated (n = 5). A PNST was considered unlikely in each case based on immunohistochemical expression of desmin and/or the lack of typical ultrastructural features, such as basal lamina. Electron microscopy was pivotal for the subclassification of canine PWTs, and the results support the hypothesis that canine PWTs represent a continuum paralleling the phenotypic plasticity of vascular mural cells. The hypothesis that a subgroup of PWTs could arise from a pluripotent mesenchymal perivascular wall cell was also considered and may explain the diverse differentiation of canine PWTs.

Malignant orbital schwannoma with massive intracranial recurrence

BACKGROUND

A 62 year old male presented with progressive diplopia, left orbital pain and impairment of visual acuity.

METHOD AND FINDINGS

Neuroradiological investigation disclosed an orbital tumour. The lesion was totally excised. Histopathology examination revealed a malignant peripheral nerve sheath tumour (MPNST). The tumour recurred with intracranial extension. The patient died 13 months after the initial diagnosis.

CONCLUSIONS

To our knowledge, this is the first reported example of a massive intracranial recurrence of an orbital MPNST. The epidemiological features, clinical course and treatment of these lesions are discussed.

A case of fibroblastic low-grade malignant peripheral nerve sheath tumor--a true neurofibrosarcoma

The authors report a case of low-grade retroperitoneal malignant peripheral nerve sheath tumor (MPNST) showing Schwannian and fibroblastic differentiation in individual tumor cells. The tumor was detected in a 29-year-old male and posed diagnostic difficulty because of the unusual morphologic and immunophenotypic features. Morphologic examination of the H&E sections revealed a rather circumscribed, highly vascular, moderately cellular spindle cell tumor. The neoplastic cells were arranged in vague, short fascicles, distributed haphazardly amid hemangiopericytoma-like vascular channels, and showed occasional whorls. Myxoid stroma and keloid-like collagen bundles were frequently seen. There were satellite nodules outside the main tumor mass and low mitotic activity but no necrosis. The tumor cells stained strongly and diffusely for both S-100 protein and CD34. Electron microscopy revealed cells with processes and focal lamina, and prominent rough endoplasmic reticulum. Although the capacity of MPNST to exhibit divergent differentiation is well known, fibroblastic differentiation is generally poorly and inconsistently documented. The present case represents an unambiguous demonstration of the co-expression within individual tumor cells of Schwannian and fibroblastic differentiation in a low-grade MPNST. The literature on this subject is reviewed.

Malignant peripheral nerve sheath tumor of the orbit: case report and literature review

A 68-year-old woman with progressive visual loss and exophthalmos in her right eye had been operated on for a mass in her right calf 3 years earlier. Imaging showed a huge mass invading the orbital structures and temporal pole. The presumptive diagnosis was a malignant orbital tumor. The tumor was resected totally and eroded tissues such as the lateral rectus muscle and dural compartments were repaired. The histological diagnosis was a malignant peripheral nerve sheath tumor (MPNST). The patient recovered uneventfully and was discharged 8 days after surgery. Two years later she died from a liver tumor. Few MPNSTs involving the orbit have been reported.

[A resected case of malignant peripheral nerve sheath tumor (MPNST) necessary to distinguish from Askin tumor]

We have treated a patient with malignant peripheral nerve sheath tumor (MPNST) for 7 years by interdisciplinary therapy. The diagnosis and treatment are reported with the clinical course so far. A 20-year-old man underwent surgical resection of a tumor on the left side of the chest in 1990, and a diagnosis of Askin tumor was made. In 1993, the disease recurred in the left axilla and was surgically resected. The surgical specimen was investigated histologically, and a diagnosis of MPNST was made instead of Askin tumor. Recently, a tumor began to grow in the left pleural cavity and was surgical resected. The tumor tissue contained both cells with oval and long spindle nuclei, which were intermingled with each other. Immunohistochemically, the tumor cells were positive for vimentin and some of them were positive for S100 protein. Because electron microscopy showed cytoplasmic processes on the tumor cell and basal lamina-like structures, a diagnosis of recurrent MPNST was made. Because this lesion resembled Askin tumor in its clinical manifestations and histological characteristics, differential diagnosis from Askin tumor was necessary. When a malignant soft tissue tumor arising from the mediastinum or chest walls is detected, immunohistochemical and electron microscopic studies should be performed. The diagnosis should be based on the overall findings including the location and clinical data.

Perineurial malignant peripheral nerve sheath tumor (MPNST): a clinicopathologic, immunohistochemical, and ultrastructural study of seven cases

Most malignant peripheral nerve sheath tumors (MPNST) are schwannian in nature. The pathologic features of MPNST with perineurial cell differentiation remain to be characterized. To determine the clinicopathologic, immunohistochemical, and ultrastructural characteristics of perineurial MPNST, 121 MPNST from the Mayo Clinic Tissue Registry were examined. Of these 23 spindle cell tumors with long processes disposed in whorls or storiform patterns, features typical of perineurioma, were studied. On the basis of immunohistochemistry (epithelial membrane antigen+/S-100-), 5 perineurial MPNST were identified among 23 tumors selected. These and two previously characterized perineurial MPNST are the subject of this study. None of seven tumors was associated with NF-1. Patients included five males and two females ranging in age from 11 to 83 years (mean, 45.7 years). The tumors measured 1.5 to 30 cm (mean, 9.1 cm) and arose in the extremities (two), trunk (two), face (one), mediastinum (one), and retroperitoneum (one). Only one tumor was nerve associated (phrenic nerve). All tumors were surgically removed. No encapsulation or neurofibroma components were noted. Necrosis was seen in three lesions. Four tumors were classified as high-grade malignant and three as low grade. Mitotic indices varied from 1 to 85/10 high-power fields (median, 16). Immunoreactivities included epithelial membrane antigen (100%), vimentin (100%), Leu-7 (57%), and CD34 (14%). Stains for S-100 protein, muscle markers, and cytokeratin were nonreactive. Ultrastructurally, perineurial-like cells were noted in three tumors and cells intermediate between perineurial and Schwann cells in one. Four tumors recurred and two metastasized; no deaths of disease were noted at follow-ups of 28 to 98 months (mean, 66.9). In conclusion, 4% of MPNST show perineurial cell differentiation. An NF-1 association has yet to be described. Nerve involvement is infrequent. Their immunophenotype (epithelial membrane antigen+/S-100-) frequently indicates ultrastructural perineurial differentiation. The prognosis of perineural MPNST appears to be more favorable than that of conventional MPNST.

Primary intraosseous malignant peripheral nerve sheath tumor: a case report and review of the literature

Primary intraosseous malignant peripheral nerve sheath tumors (MPNST) are exceptionally rare; the case reported here represents the first documented example occurring in the spinal column. The tumor arose in the second cervical vertebra of a forty year old woman of Asian origin. She had no stigmata of von Recklinghausen's disease (VRD). Plain radiographs and magnetic resonance imaging showed an osteolytic lesion within the expanded body of the vertebra. Histology revealed spindle-shaped tumor cells with nuclei showing pleomorphism, pallisading and mitotic activity. The cells stained positively for S-100 protein. The patient underwent stabilisation of the cervical spine and tumor excision as a two-stage procedure. She died of pulmonary metastases one year later. We have reviewed the literature on the pathology of these tumors.

Subdiaphragmatic and intrathoracic paraspinal malignant peripheral nerve sheath tumors: a clinicopathologic study of 25 patients and 26 tumors

BACKGROUND

To determine the effects of anatomic site on the presentation and diagnosis of malignant peripheral nerve sheath tumors (MPNSTs) and on the treatment and outcomes of the patients, the authors initiated a study of these tumors at different sites. An earlier report described MPNSTs of the buttock and lower extremity, and the current series analyzes those presenting at intrathoracic (IT) and subdiaphragmatic (SD) paraspinal sites.

METHODS

The authors reviewed data on patients with paraspinal MPNSTs who were seen at Memorial Hospital during the period 1960-1995 and for whom histologic slides were available. Various clinicopathologic parameters and their effects on patient outcomes were examined.

RESULTS

Twenty-five patients with 26 tumors were evaluated. Seven tumors were IT and 19 were SD; 60% of the patients had neurofibromatosis type 1 (NF1). Most patients presented with pain, and a diagnostic delay (of 3 months to 2 years) was often noted. Mean tumor sizes for SD and IT tumors were 14.3 cm and 6.6 cm, respectively. Most MPNSTs were composed of spindle cells in fascicles. Twenty-seven percent exhibited divergent differentiation. Twenty-four tumors were high grade, and a low grade component was identified in 8 tumors. Surgical resection was attempted for 23 tumors (88%), but complete resection was achieved in only 6 cases (23%). Eighty percent of the patients died of their tumors, 2-year and 5-year survival rates were 35% and 16%, and median survival was 8.5 months. Significant prognostic factors were tumor size <5 cm, the presence of a low grade component, and complete tumor resection.

CONCLUSIONS

Paraspinal MPNSTs have more aggressive behavior than peripherally located tumors, mainly because of the difficulty encountered in resecting them completely. Prognoses of patients with MPNST at this site appear to be affected by resection status, tumor size, and tumor grade.

Malignant schwannoma located in the retroauricular region

There have been no reports about malignant Schwannoma located retroauricularly in the medical literature we reviewed. Malignant Schwannoma is a very malignant tumor, which is rare. For diagnosis, microscopic and immunohistochemical studies are needed. It is often seen together with neurofibromatosis. The prognosis is very poor and the only available treatment is surgical excision. Although it is known that both radiotherapy and chemotherapy are not effective, we achieved good outcome with this combination applied postoperatively.

Primary epithelioid malignant schwannoma of the lung

This is the first documented report of a case of primary malignant nerve sheath tumor of the lung showing an epithelioid malignant schwannoma. A 55 year old Japanese female underwent lobectomy of the middle lobe of the right lung because of a large, rounded tumorous shadow found on chest X-ray film. Light microscopic examination of the neoplasm disclosed an epithelioid malignant schwannoma with foci having a spindle-cell sarcomatous pattern. The neoplastic cells were positive for S-100 protein and neuron specific enolase by the immunoperoxidase method. Transmission electron microscopy showed basement membrane-like material surrounding the neoplastic cells and long spacing collagens in the interstitial spaces. The patient died of a recurrent tumor in the right hemithorax 5 months after undergoing lobectomy. An autopsy revealed no primary site of the neoplasm outside the lung. Furthermore, there was no evidence of neurofibromatosis.

Malignant peripheral nerve sheath tumors: an immunohistochemical study in relation to ultrastructural features

The constituent cells in malignant peripheral nerve sheath tumors were examined by studying the expression of immunohistochemical markers for Schwann cells and perineurial cells in relation to ultrastructural features in 12 malignant peripheral nerve sheath tumors. Ultrastructural studies demonstrated mixed proliferation of Schwann cells, perineurial cells, fibroblastic cells, and primitive cells in many malignant peripheral nerve sheath tumors. Expression of S-100 protein was well correlated with Schwann cell-like differentiation of tumor cells. However, Leu-7 and epithelial membrane antigen, which have been considered to be specific to Schwann cells and perineurial cells, respectively, were common to Schwann cells, perineurial cells, and primitive cells. The common immunophenotypic expression suggests a close relationship among these cell types. The unusual expression of cytokeratin could be explained by the plasticity of intermediate filament expression.

Peripheral nerve sheath differentiation in malignant soft tissue tumours: an ultrastructural and immunohistochemical study

Thirteen soft tissue sarcomas with ultrastructural evidence of nerve sheath differentiation were investigated by immunohistochemistry. Three arose in a major nerve or nerve trunk and four patients had von Recklinghausen's neurofibromatosis. Ultrastructurally, 10 cases showed variable differentiation towards Schwann cells, two resembled perineurial cells and one tumour had features suggestive of both cell types. Immunostaining for S-100 protein was positive in eight Schwann cell tumours, negative in the other two Schwann cell tumours and negative in those with perineurial-like cells. No cases demonstrated epithelial membrane antigen, so that the existence of perineurial cells in malignant nerve sheath tumours remains immunohistochemically unsubstantiated; it may be that the perineurial-like cells are merely incompletely differentiated Schwann cells, with nerve sheath differentiation manifesting a continuous spectrum. Leu 7 was detected in four Schwann cell tumours, three of which were ultrastructurally well differentiated. Cytokeratin and desmin were demonstrated only in an undifferentiated pleomorphic area of one Schwann cell tumour. Electronmicroscopy can aid diagnosis by revealing nerve sheath differentiation in malignant soft tissue tumours without demonstrable S-100 protein.

Bronchial neurofibrosarcoma

A 56-year-old woman was seen with the clinical features of collapse of the right lower lobe. Intrabronchial extension of a tumor was demonstrated endoscopically. Sleeve bilobectomy was performed, and a diagnosis of bronchial neurofibrosarcoma was confirmed by light and electron microscopic and immunohistochemical studies.

Recurrence of acoustic neurilemoma as a malignant spindle-cell neoplasm. Case report

A 75-year-old man presented with a right cerebellopontine angle tumor 11 months after complete macroscopic resection of a right acoustic neurilemoma. Histological examination of the recurrent tumor showed a malignant spindle-cell neoplasm with positive staining for S-100 protein. The patient had no stigmata of von Recklinghausen's disease. It is proposed that this recurrence represents progression from a benign to a malignant acoustic nerve-sheath tumor, an event that is extremely rare outside the clinicopathological context of neurofibromatosis.

Characterization of cultured neurofibroma cells derived from von Recklinghausen's disease

We have examined the cytoplasmic distribution of actin and fibronectin in cultured neurofibroma cells (NF cells) derived from a patient with von Recklinghausen's disease by using phase contrast and indirect immunofluorescence microscopy. NF cells were larger in size and more dendritic in shape compared to normal human dermal fibroblasts. NF cells also showed abundant granular staining of actin and a decrease in the linear staining pattern of fibronectin. Furthermore, employing a colony-formation assay on the top of an agar-gel in the presence of fibroblast growth factor (FGF), normal fibroblasts showed a significant number of colonies, whereas NF cells did not demonstrate colony formation even after addition of FGF. These findings suggests that NF cells from patients with von Recklinghausen's disease may have different characteristics when compared with normal fibroblasts, and that NF cells are similar to transformed cells with regard to their actin and fibronectin distribution.

Malignant schwannoma arising in the intracranial trigeminal nerve. A report of an autopsy case and a review of the literature

An autopsy case of malignant schwannoma arising in the intracranial trigeminal nerve is reported. The tumor involved the right cerebellopontine angle of the brain stem in an 18-year-old man. The spindle-shaped tumor cells with eosinophilic cytoplasm proliferated in fascicles and exhibited hypercellularity, pleomorphism, increased mitotic activity and invasive growth. Ultrastructurally, interdigitating cytoplasmic processes and a few fragmented basal lamina-like structures were observed. Immunohistochemically, some tumor cells were reactive with conventional anti-S-100 protein antibody, but negative for beta subunit. Most tumor cells were positive for alpha subunit of S-100 protein. This is the eighth reported case of malignant schwannoma arising in the intracranial trigeminal nerve.

Neurofibrosarcoma of skin and subcutaneous tissues

In this report, we describe 13 cases of primary neurofibrosarcoma of the skin. The tumor presumably arises from small cutaneous nerves, is locally aggressive, and has a potential for metastasis. Characteristic histopathologic features include proliferating atypical spindle cells with slender wavy and pointed nuclei; hypocellular areas with loose, myxoid stroma; and areas of organoid organization such as palisading, whorly, storiform, and tactile body-like formations. The S-100 stain is positive in about 60% of cases. In the current series, most tumors arose in deep dermis and were grade 2 malignant lesions with a moderate degree of cytologic atypia and 2 or fewer mitoses in 10 high-power fields. Three patients died of their malignant lesion. Only two tumors metastasized. Of the 10 patients who had local recurrence, 5 had multiple recurrent lesions. Neurofibrosarcoma should be considered in the differential diagnosis of malignant tumors of the skin. A complete surgical resection of the primary tumor with adequate margins of surrounding normal-appearing tissue is advised.

Primary omental tumor with ultrastructural features of cellular schwannoma and absence of S-100 antigen reactivity

We report a primary well-delimited, large mesenchymal omental neoplasm which appeared in a 58 year old man without neurofibromatous traces. The histological and ultrastructural features were consistent with a Schwann cell origin. However, repeated immunohistochemical reactions failed to demonstrate protein S-100 antigen reactivity in the neoplastic cells, the latter only expressing vimentin. The differential diagnosis with hemangiopericytoma is proposed.

Malignant epithelioid schwannoma: a light microscopic and immunohistochemical study

Malignant epithelioid schwannoma is a rare variant of malignant nerve sheath tumor that can be confused with both other neuroectodermal neoplasms and carcinomas. The light microscopic and immunohistochemical findings of a malignant epithelioid schwannoma arising in the mandibular region of a 27-year-old female are described. The differential diagnosis of this unusual neoplasm from malignant melanoma and poorly differentiated carcinoma is discussed.

Heterogeneity of malignant schwannomas

Six malignant schwannomas were studied by electron microscopy and immunohistochemistry for S-100 protein at the light and electron microscopic levels to clarify the nature of the tumor cells. Three tumors (group A) were composed of poorly differentiated tumor cells and showed no immunoreactivity for S-100 protein. One tumor (group B) was composed of perineurial cells that were S-100 protein-negative. Two tumors (group C) consisted of both Schwann cells and fibroblastic cells like neurofibromas, and only the former were found to contain S-100 protein. Thus, this study showed the heterogeneous nature of the malignant schwannomas and suggested that these tumors might arise from multipotential Schwann cells or different cellular components of peripheral nerve or primitive cells.

Malignant melanotic schwannoma of the bronchus

A case of malignant melanotic schwannoma arising in the right upper lobe bronchus of a 27 year old man is presented. Tumours of this type most commonly occur in spinal nerve roots and are generally considered to be benign. The behaviour of those originating elsewhere is less predictable. As far as we are aware this is the first reported case affecting the respiratory tract.

Malignant schwannoma of the mandible

A case of malignant schwannoma occurring in the mandible of a 76-year-old Japanese woman is presented. Results of the gross examination are described as well as the surgical procedure. Details of the staining techniques for examination of the biopsy specimen are given. The histopathological findings are mentioned including those obtained from radiographic, microscopic, and electron microscopic examination. A discussion of the disease and of its difficulty of diagnosis follows.

Malignant schwannoma of the ovary. Report of a case

A malignant schwannoma, apparently arising in the left ovary of a 71-year-old woman is described. The patient had no stigmata of von Recklinghausen's disease. The tumor was located in the position of the left ovary and had metastasized throughout the peritoneal cavity. The neural sheath origin of the tumor was confirmed by electron microscopic examination. The tumor is thought to have arisen from small nerves in the ovarian hilus.

Epithelioid malignant schwannoma. A study of 14 cases

We report a light and electron microscopic, immunohistochemical, clinical and prognostic study of 14 patients with epithelioid malignant schwannoma. In 8 patients the tumour involved a major nerve. The tumours were rather small in most instances, the largest diameter being less than 5 cm in 7 cases. Light microscopically, they showed highly cellular areas of epithelioid, polygonal or rounded cells characteristically forming cords and rows and arranged in nodules of varying size. Spindle cell sarcoma areas as in classical malignant schwannoma were seen in 9 cases, and neurofibromatous areas in one case. Four cases were entirely epithelioid in appearance. Electron microscopically the epithelioid tumour cells showed nuclei with mostly even contours containing one or two trabecular or reticular nucleoli, cytoplasmic projections, intra-cytoplasmic myelin-like figures, intercellular junctions and discontinuous, sometimes multilayered external lamina material. The ultrastructural findings indicate that epithelioid malignant schwannoma is a tumour of neural crest derivation having features of Schwann cell differentiation. Immunohistochemically, S-100 protein was demonstrated in 7 tumours and neuron specific enolase in 3. There was a female predominance, 9/14, and a median age of 38.5 years (range 17-74). The extremities, including the hip and shoulder regions, were the most common sites, 12/14. The tumour proved highly malignant; 9 of 14 patients were dead at the time of follow-up and a high incidence of metastasis (7 of 14) was observed.

Malignant peripheral nerve sheath tumors. A clinicopathologic study of 120 cases

A review was done of 120 cases of malignant peripheral nerve sheath tumor (MPNST) seen during a 71-year period. Of the 120 patients, 52 were males and 68 were females with a mean age at diagnosis of 35.3 years; 12 patients were younger than 20 years. The series included 62 (52%) patients with neurofibromatosis, 13 (11%) with postradiation sarcomas, and 19 (16%) with metaplastic foci. The incidence of MPNST arising in neurofibromatosis was 4.6% in the current series and 0.001% in the general clinic population. Tumors greater than 5 cm and the presence of neurofibromatosis adversely affected the prognosis (P less than 0.05). When both features were present, survival was greatly decreased. Patients with tumor in the extremities did better than those with head or neck lesions. Metaplastic foci or previous radiation at the tumor site did not alter the prognosis. Each tumor was graded 1 to 4 on the basis of cellularity, pleomorphism, mitotic index, and necrosis. No significant correlation was noted between survival and either grade or mitotic rate. Survival was improved when total rather than subtotal resection was done. This was most marked in patients with a small lesion, which may reflect the difficulty in adequately excising large tumors. Adjuvant radiation or chemotherapy did not appear to affect survival. The MPNST is an aggressive uncommon neoplasm, and large tumor size, the presence of neurofibromatosis, and total resection are the most important prognostic indicators.

Neurofibromatosis and associated neuroectodermal tumors: a congenital neurocristopathy

The synchronous occurrence of neurofibromatosis and neuroblastoma has been labeled in the recent literature as a chance event. We report 2 cases of newborn infants with congenital neurofibromatosis and a similar midline pattern of multiple Schwann cell and neuroblastic tumors; other types of ectomesenchymal tumor differentiation are documented, along with supportive ultrastructural and immunohistochemical studies. The tumors may take an aggressive, fatal course despite maximal multimodality antitumor therapy. These 2 cases are reported, with additional literature review, to document a clinically recognizable neurocristopathy that links neuroblastic tumors and neurofibromatosis.

Epithelioid neurilemmoma of the trigeminal nerve: an immunohistochemical and ultrastructural study

A 50-year-old male presented with facial pain due to an extrinsic intracranial tumour involving pontine nerve roots. Biopsy and subsequent partial surgical excision indicated origin from the trigeminal nerve. Histologically the tumour had features of a neurilemmoma but in addition contained a population of epithelioid cells. Immunohistochemical studies demonstrated S100 protein in the non-epithelioid component but no reaction in the epithelioid cells, whilst vimentin was present in both cell types. Ultrastructurally the epithelioid cells showed features consistent with a Schwann cell nature and may represent a less well differentiated cell population derived from a Schwann cell precursor. The significance of these findings in relation to the cell of origin of neurilemmomas is discussed.