Studies on experimental malignant nerve sheath tumors maintained in tissue and organ culture systems. II. Electron microscopy observations

Intraoral perineurioma, soft tissue type: report of five cases, including 3 intraosseous examples, and review of the literature

Soft tissue type perineuriomas (STP) are uncommon tumors, oral examples being very rare. They have been described in the mandible, gingiva, lips, retrotonsillar mucosa and maxillary vestibule. Herein, we report the clinicopathologic features of five STP, two affecting the buccal mucosa and three the mandible. Three patients were women and two men. All tumors were characterized by a proliferation of cytologically bland, mitotically inactive spindled cells with round, ovoid or spindled nuclei, embedded in a variably collagenous and myxoid matrix. Interestingly, two mandibular tumors featured psammoma bodies and one, in addition, contained irregular calcifications. Tumor cells showed the immunohistochemical profile of perineurial cells including epithelial membrane antigen, Glut-1, claudin-1 and collagen type IV. S100 and neurofilament proteins were not expressed by the tumor cells. A few minute, peripherally situated, entrapped nerves were identified. All tumors were reported gross-totally excised and no recurrences have taken place. The clinical characteristics of STP are summarized and its differential diagnosis relative to other spindle cells tumors and meningioma is discussed.

Lucien J. Rubinstein: enduring contributions to neuro-oncology

Dr. Lucien Rubinstein is best remembered for his significant contributions to the field of neuropathology, particularly in the classification of nervous system tumors. His accomplishments in basic neuro-oncology and in the formulation of diagnostic principles reflected a unique talent for synthesizing fundamental clinicopathological concepts based on skillful diagnostic investigation and a thorough understanding of neurobiology. Dr. Rubinstein was the leader in the establishment of cell cultures from central nervous system (CNS) tumors. He meticulously analyzed both light and electron microscopic features of CNS tumors, recorded his findings, and patiently drew sketches to be shared generously with his colleagues and students. As a pioneer in neuropathology, in his work Dr. Rubinstein set the foundation for many enduring concepts in neurosurgery, neuro-oncology, neurology, and basic tumor biology.

Tumor suppressor mutations and growth factor signaling in the pathogenesis of NF1-associated peripheral nerve sheath tumors: II. The role of dysregulated growth factor signaling

Patients with neurofibromatosis type 1 (NF1), one of the most common genetic disease affecting the nervous system, develop multiple neurofibromas that can transform into aggressive sarcomas known as malignant peripheral nerve sheath tumors (MPNSTs). Studies of human tumors and newly developed transgenic mouse models indicate that Schwann cells are the primary neoplastic cell type in neurofibromas and MPNSTs and that development of these peripheral nerve sheath tumors involves mutations of multiple tumor suppressor genes. However, it is widely held that tumor suppressor mutations alone are not sufficient to induce peripheral nerve sheath tumor formation and that dysregulated growth factor signaling cooperates with these mutations to promote neurofibroma and MPNST tumorigenesis. In Part I of this review, we discussed findings demonstrating that a loss of NF1 tumor suppressor gene function in neoplastic Schwann cells is a key early step in neurofibroma formation and that progression from neurofibroma to MPNST is associated with abnormalities of additional tumor suppressor genes, including p53, INK4A, andp27(kip1). In Part II of this review, we consider evidence that dysregulated signaling by specific growth factors and growth factor receptors promotes the proliferation, migration, and survival of neoplastic Schwann cells in neurofibromas and MPNSTs.

Constitutive activation of the neuregulin-1/ErbB receptor signaling pathway is essential for the proliferation of a neoplastic Schwann cell line

Neuregulin-1 (NRG-1) proteins promote Schwann cell survival, differentiation and proliferation during development. High levels of an NRG-like activity are also present in some human peripheral nerve sheath tumors, suggesting that NRG-1 isoforms may be involved in the development of these neoplasms. We examined the expression of NRG-1 and its receptors, the erbB membrane tyrosine kinases, in JS1 cells, a rapidly proliferating line derived from a chemically induced rat malignant peripheral nerve sheath tumor (MPNST). Relative to nontransformed Schwann cells, JS1 cells overexpress the NRG-1 receptor erbB3 and its erbB2 coreceptor; JS1 erbB2 transcripts show no evidence of the activating mutation commonly found in N-ethyl-N-nitrosourea-induced neoplasms. JS1 cells do not express the epidermal growth factor receptor (EGFR), a kinase implicated in the pathogenesis of a major subset of MPNSTs. JS1 cells also express mRNAs encoding multiple alpha and beta isoforms from the glial growth factor and sensory and motor neuron-derived factor NRG-1 subfamilies. Stimulation with NRG-1beta in the presence of forskolin produces a dose-dependent increase in JS1 DNA synthesis. Even in unstimulated JS1 cells, however, erbB2 and erbB3 are constitutively tyrosine phosphorylated. Reducing this constitutive phosphorylation with the specific erbB inhibitor PD158780 markedly impairs JS1 DNA synthesis. These observations support the hypothesis that NRG-1 isoforms and erbB kinases act in an autocrine and/or paracrine fashion to promote mitogenesis in JS1 cells. The absence of EGFR expression in JS1 cells suggests that constitutive activation of the NRG-1/erbB signaling pathway is an alternative means of inducing Schwann cell neoplasia.

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.

Cell culture studies on human nerve sheath tumors

The main controversy about nerve sheath tumors (NSTs) has been their histogenesis. A Schwann cell origin has been proposed by many investigators for both schwannomas and neurofibromas. However Erlandson and Woodruff observed that while schwannomas appeared to be composed predominantly of Schwann cells, neurofibromas consisted of mainly perineurial cells. In addition, variable numbers of fibroblast-like cells and intermediate cells also have been reported in the 2 lesions. Whether these represent distinct cell types or variants of Schwann cells is still debatable. In an attempt to solve this controversy, the present study was undertaken to observe the morphology and the behaviour of these tumors in culture. These studies showed that all nerve sheath tumors are basically of Schwann cell origin and that intermediate cells and fibroblasts are variants of Schwann cell. Tissue culture studies done chiefly on schwannomas showed that the morphological features of schwannomas are preserved in 'in vitro culture' condition and therefore the difference between neurofibroma and schwannoma appears to be due to inherent differentiating property of the Schwann cells along with some environmental stimulus.

Localized hypertrophic mononeuropathy involving spinal roots and associated with sacral meningocele. Case report

Hypertrophic nerve lesions displaying onion-bulb cellular formations are quite rare in the absence of a generalized hypertrophic neuropathy. The isolated peripheral nerve lesion has been termed "localized hypertrophic mononeuropathy" (LHN), and fewer than 30 cases of this condition have been reported. Very little is known regarding the etiology and the natural course of this rare disorder. A unique case of LHN afflicting spinal roots in association with a sacral meningocele is reported with a brief review of the relevant literature. The unique features of this case not only reveal a variable clinical presentation of the disease but also support the theory that LHN may be a localized reaction to nerve trauma or entrapment.

Cutaneous plexiform schwannoma in a pig

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

Studies on the cellular origin of neurothekeoma: clinical, light microscopic, immunohistochemical, and ultrastructural observations

The clinical, histopathologic, and immunohistochemical features of 11 cases of neurothekeoma are reported. One case was examined by electron microscopy. The mean age of the patients was 27.1 years; the study comprised eight female and three male patients. Most lesions were nondescript papules and located on the upper part of the body, seven cases of neurothekeoma on the head. Eight cases were classified as cellular neurothekeoma on the basis of a striking fascicular pattern and three cases as myxomatous neurothekeoma because of prominent myxoid stromal change. All cellular neurothekeomas failed to express S-100 protein, whereas the three myxomatous types were strongly positive for this marker. Other than vimentin, there was no significant immunoreactivity with other immunohistochemical markers. Ultrastructural study of one case of cellular neurothekeoma was inconclusive for cell type although a perineurial origin could not be excluded. On the basis of these results, we conclude that cellular neurothekeoma differs from myxomatous neurothekeoma not only by clinical and histologic findings but also by immunoreactivity with S-100 protein. These findings also suggest the existence of two distinct subtypes of neurothekeoma and possible origin of the two variants of neurothekeoma from different cell types or at least variation in phenotypic expression of a common cell type. On the other hand, it cannot be excluded that these two variants are different stages in the natural history of neurothekeoma.

The enigmatic perineurial cell and its participation in tumors and in tumorlike entities

The perineurial cells that make up the perineurium of peripheral nerve fascicles are characterized by distinct ultrastructural features, including non-branching thin cytoplasmic processes coated by an external lamina and joined at their ends by a tight junction, few organelles, actin and vimentin filaments, and numerous pinocytotic vesicles. Perineurial cells are immunoreactive for vimentin and epithelial membrane antigen (EMA) but not for the Schwann cell markers S-100 protein and Leu-7. The cytogenesis of the perineurium remains disputable, with morphologic, immunohistochemical, and experimental evidence supporting origin from the fibroblast, Schwann cell, and arachnoid cap cell. Ultrastructural studies more recently supported by immunolocalization of EMA have detected hyperplastic and neoplastic perineuriallike cells in a number of pseudoneoplastic lesions and true neoplasms, notably localized hypertrophic neuropathy, neurofibromas of various types, and perineurioma.

Significance of degenerating endoneurial cells in peripheral neuropathy

In 42 human sural nerve biopsies degeneration of endoneurial cells was evaluated semiquantitatively at the electronmicroscopic level. These cells were of non-Schwannian origin since they were not surrounded by a basement membrane. Most of the degenerating cells resembled endoneurial fibroblasts: their remaining cytoplasmic processes were quite extensive, not finger-like as in macrophages, and their cytoplasm did not contain conspicuous lysosomes or phagolysosomes that would identify them as degenerating macrophages. Criteria for regarding these cells as degenerating were defects of the cytoplasmic surface membrane with extracellularly situated organelles. The ratio between normal and degenerating endoneurial cells in five different groups of peripheral neuropathies was compared to a group of normal controls. No degenerating endoneurial cells were found in the latter. The largest proportion of degenerating endoneurial cells was noted in patients with panarteritis nodosa (30% of the endoneurial cells evaluated). Between 9% and 18% of the evaluated endoneurial cells were seen degenerating in hereditary motor and sensory neuropathies, in neuropathies associated with IgG or IgM gammopathy, and in chronic demyelinating inflammatory polyradiculoneuropathy. These findings suggest that degeneration of endoneurial cells is a nonspecific sign of peripheral neuropathy occurring in various types of neuropathy, although vasculitis represents the most frequent cause. Thus, degeneration of endoneurial cells can be added to the growing list of changes that possibly indicate an inflammatory disorder, even during the intervening stage when apparent inflammatory cell infiltrates are lacking.

A retrospective survey of endocardial proliferative lesions in rats

Sixty, proliferative, endocardial lesions were diagnosed in 19,304 rats, for an overall incidence of 0.3%. This population consisted of 10,127 Fischer 344, 8,737 Wistar, 200 Sprague-Dawley, and 240 Long Evans rats from chronic/oncogenicity studies reported at Lilly Research Laboratories from 1976 to 1988. Of the 60 proliferative lesions, 44 were classified as endocardial hyperplasia, 15 as endocardial schwannomas, and one as an endocardial sarcoma for prevalence rates of 0.2%, 0.08%, and 0.005%, respectively. Affected rats ranged in age from 42 to 110 weeks. There were no sex or treatment-related differences in the prevalence of the rat endocardial proliferative lesions. A review of endocardial lesions in 18 of 233 Wistar rats treated with carbamate derivatives revealed endocardial hyperplasia in 12 rats, schwannomas in five rats, and a sarcoma in one rat. One of the 12 rats with endocardial hyperplasia also had an intramural schwannoma. Of 200 Wistar rats given N-nitroso-N-methylurea, two had endocardial hyperplasia, and one had an endocardial schwannoma. Morphologic features were similar in either spontaneous or treatment-associated hyperplasia or neoplasia of the rat endocardium. Probable Schwann cell origin of the endocardial proliferative lesions was indicated by positive immunohistochemical staining for S-100 antigen in 10/12 spontaneous and 11/14 carcinogen-associated endocardial hyperplastic lesions. Further, 15/16 spontaneous and 6/7 carcinogen-associated neoplasms were immunoreactive to S-100. No tumor metastasis was recorded in either the spontaneously affected or carcinogen-treated rats.

Formation of nerve twig-like nests and schwannoma in an unusual case of neurofibroma

A case of unusual neurofibroma in an 18-year-old Japanese male is reported. The histology of the tumor was characterized by nerve twig-like nests intermingled with fascicular bundles. In the central portion, the tumor also contained a lobular lesion showing features characteristic of schwannoma. Immunohistochemically, the tumor cells in both the nests and the lobular lesion demonstrated a mostly positive reaction for S-100 protein. S-100 protein-positive and -negative cells were observed in equal numbers in the fascicular bundles surrounding the nests. This unusual nerve sheath tumor in which the S-100 protein-positive cells form both nerve twig-like nests and lobular schwannoma has not been reported previously. The origin of the S-100 protein-positive cells in the two lesions is also discussed.

Benign nerve sheath tumors: a light microscopic, electron microscopic and immunohistochemical study of 102 cases

One hundred and two cases of benign nerve sheath tumors (NSTs) were studied with a combined approach using routine light microscopy (LM), immunohistochemistry (IH) for myelin basic protein (MBP) and S-100 protein as well as transmission electron microscopy (TEM) with the aim of obtaining greater insight into the true nature of these neoplasms, and also to establish the importance of IH and TEM in their diagnosis. Myelin basic protein was not identified in any of these tumors, whereas S-100 protein was positive to a variable degree in both schwannomas and neurofibromas. TEM revealed that Schwann cells predominated in tumors which were strongly positive for S-100 protein and appeared as schwannomas by LM. However, neurofibromas showing a variable patchy positivity for S-100 were composed of an admixture of Schwann cells, fibroblast-like cells and intermediate cells considered to be modified Schwann cells. Perineurial cells in typical form were not seen. It is concluded that all NSTs are basically of Schwann cell origin and that the intermediate cells and fibroblast-like cells are variants of Schwann cells. The different morphological appearances and biological behaviour of schwannomas and neurofibromas may be related to some other factors like micro-environment or genetic predisposition. Further, both IH, especially for S-100 protein, and TEM play an important role in establishing their diagnosis.

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.

Brain tumours in childhood in Bombay: I: Histopathology showing changing patterns; II: Tissue culture with light and electronmicroscopy, stressing ingestion & degradation of bacteria by glial cells in vitro

The pathological pattern of 86 brain 'tumours' in childhood during the years 1981-85 (out of a total of 586 for all ages), showed a higher proportion of neoplasms and a much lower of tuberculomas compared to the preceding three decades. A large number of histologically unusual cases was revealed. Through tissue culture of brain tumours we carried out morphological, histochemical and fine structural study of the tumour cells in vitro. The abundant presence of lysosomal acid phosphatase, in outgrowing cells, correlated with the detection of lysosomal dense bodies and vacuoles in araldite sections, by light and electronmicroscopy. In view of the phagocytic propensity of schwann cells for M. leprae as the important factor in leprous neuritis, TC preparations of gliomas, (in addition to acoustic schwannomas and meningiomas), were inoculated with two mycobacteria, M. scrofulaceum and the ICRC bacillus. There was a pronounced intracytoplasmic uptake, i.e. endocytosis, of acid-fast bacilli by the growing cells of these tumours. This was confirmed by electronmicroscopy which showed intact and degrading bacilli in various stages, in such cells of a typical cerebral astrocytoma used as an illustrative case in this paper. Ingestion and Digestion appear to be an inherent property of growing tumour cells in vitro. Fine structural examination of in vitro growth of an unusual subependymal giant cell astrocytoma, not inoculated with bacilli, served as a control. Cells of both tumours showed copious autophagic activity and cytoskeletal features of developing microtubules and filaments.

Immortalized rat Schwann cells produce tumours in vivo

We have recently reported the immortalization of primary Schwann cells isolated from sciatic nerves of normal neonatal rats. The cells were maintained under continuous mitogenic stimulation with glial growth factor and forskolin, achieving immortalization after 12 to 15 weeks without the use of viral infection, oncogene transformation or chemical carcinogens. The immortalized cells (1.17 cells) initially retain the capability to recognize and attach to peripheral neurons in culture as well as the ability to myelinate those neurons. The functional capacity of the cells gradually diminishes in culture, such that late passage cells can ensheath neurons but cannot form a myelin sheath. Both normal and immortalized cells secrete comparable amounts of autocrine growth factor activity in culture that can be regulated by extracellular matrix proteins. The difference between quiescent and immortalized Schwann cells seems to lie not in the production of growth factor but rather in the relative ability to respond to the factor(s). To test the potential of the immortalized Schwann cells for the ability to form tumours in vivo, we injected equal numbers of primary or immortalized Schwann cells into the sciatic nerve of adult syngenic rats and allowed them to incubate there for 6 to 13 weeks, whereupon the injected nerves were inspected for tumour formation. In every case (N = 3) the primary cells had no effect whereas every injection of immortalized cells (N = 5) resulted in a solid cellular mass surrounding the injected nerve. The tumours were encapsulated masses of actively dividing Schwann-like cells that surrounded but did not invade the nerve fascicle.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term endoneurial changes after nerve transection

Long-term endoneurial changes in the distal stump of transected rat sciatic nerve were examined from 8 to 50 weeks after nerve transection. The morphological alterations were followed both in nerves which were allowed to regenerate and in nerves in which regeneration was prevented by suturing. The nerves prevented from regenerating showed markedly atrophied Schwann cell columns after 20 weeks and a disappearance of some Schwann cell columns after 30 weeks. The surrounding endoneurial fibroblast-like cells gradually lost their delicate cytoplasmic extensions and formed rough fascicles around numerous shrunken Schwann cell columns or around areas from which Schwann cells had apparently disappeared. Inside the fascicles, the Schwann cell loss was replaced by collagen fibrils or occasionally, by a dense accumulation of microfibrils. The loss of endoneurial cytoplasmic processes continued up to 50 weeks, leaving behind patches of thin fibrils around numerous shrunken Schwann cell columns or around collagenous areas where Schwann cells were lost. The endoneurial matrix showed presence of thin 25- to 30-nm collagen fibrils close to shrunken Schwann cell columns up to 50 weeks but in areas with advanced degeneration a shift towards regular 50- to 60-nm collagen fibrils occurred. The degenerated areas resembled those described in Renaut bodies and neurofibromas. Despite suturing of transected nerves to prevent sprouting, occasional regenerating sprouts were noted in the Schwann cell columns. These axons were surrounded in a sheath-like fashion by pre-existing endoneurial cell fascicles covered by a basal lamina. In the reinnervating nerves the endoneurial space gradually lost its compartmentized structures consisting of collagen fibrils and endoneurial fibroblast-like cells. After 20 weeks the endoneurial cells were inconspicuous and the extracellular matrix consisted mainly of 50- to 60-nm collagen fibrils. During axonal growth and maturation, Schwann cells containing unmyelinated axons surrounded large, myelinated axons in a collar-like fashion. Close to these collars of Schwann cells, thin 25- to 30-nm collagen fibrils were noted in focal areas, even after 50 weeks. Occasionally, numerous clusters of regenerating axonal sprouts were noted in the perineurium. These were surrounded by multiple layers of cells possessing basal lamina. The present results show that after nerve transection the distal stump of the severed nerve shows dynamic changes in the endoneurial space, especially in nerves where reinnervation is prevented.(ABSTRACT TRUNCATED AT 400 WORDS)

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 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.

Ultrastructural localization of S-100 protein in neurofibroma

The nature of the cells in neurofibromas was studied by electron microscopy and immunoelectron-microscopic examination of S-100 protein. Ultrastructurally, all five neurofibromas studied were found to be composed of Schwann cells, perineurial cells, and intermediate cells, which had features of both perineurial cells and fibroblasts. The Schwann cells had complex, branched cytoplasmic processes and a continuous basal lamina. The perineurial cells were distinguishable from Schwann cells by the presence of numerous pinocytotic vesicles, unbranched slender cytoplasmic processes and a discontinuous basal lamina. The intermediate cells had no basal lamina, but were topographically related to Schwann cells and had a similar fine structure to that of perineurial cells. Thus, they seemed to be modified neoplastic perineurial cells. Immunoelectron-microscopic studies showed the presence of cells with and without S-100 protein in the neurofibromas: cells with S-100 protein resembled Schwann cells ultrastructurally, and those without S-100 protein were perineurial and intermediate cells. Some Schwann cells with S-100 protein in one neurofibroma had numerous pinocytotic vesicles characteristic of perineurial cells, suggesting that Schwann cells and perineurial cells are functional variants of the same cell type. Thus this study showed that neurofibromas were composed of Schwann cells with S-100 protein and perineurial and intermediate cells, including so-called endoneurial fibroblasts, without S-100 protein. Morphological and functional transition seems to occur between Schwann cells and perineurial cells, and between perineurial cells and intermediate cells.

Dermal nerve sheath myxoma. A light and electron microscopic, histochemical and immunohistochemical study

Two cases of dermal nerve sheath myxoma have been examined by light and electron microscopy, and by immunohistochemical and histochemical methods. The nomenclature of this tumor has been debated, and the histogenesis unsettled. Light microscopically, the lobulated myxoid tumors were generally composed of spindle-shaped and stellate tumor cells in an abundant matrix of mucosubstances. Ultrastructural features indicated an origin from the peripheral nerve sheath; among the pertinent findings were a single or duplicated external lamina investing the cells, desmosome-like junctions, cytoplasmic microfilaments and myelin figures, and interdigitating cytoplasmic processes. S-100 protein was demonstrated by means of the immunoperoxidase technique within both tumors, further supporting this origin. The histochemical analysis of the mucosubstance showed the presence of sulphated glucosaminoglycans. The name dermal nerve sheath myxoma, suggested by Harkin and Reed, is recommended.

Elephantiasis neuromatosa. A light, immunohistochemical and electron microscopic study

An example of elephantiasis neuromatosa, an unusual variant of neurofibromatosis, coexistent with lipomatosis is presented. This dual cell population produced a diffuse swelling of the gluteal sulcus of a young female. The neurogenous origin of the spindle cell component was substantiated by immunoreactivity for S-100 protein as well as by the fine structural observation of a regular basement membrane coating and a profusion of Luse bodies. As far as can be ascertained, this is the first reported immunohistochemical and ultrastructural study of this particular variant of peripheral nerve sheath lesion.

Diagnostic aspect of spindle-cell sarcomas by electron microscopy

Spindle-cell sarcomas in the somatic soft tissue and soft parts, including fibrosarcoma, leiomyosarcoma, malignant fibrous histiocytoma (MFH), and malignant schwannoma were examined by electron microscopy in order to delineate the most reliable cellular features for their diagnosis. Fibrosarcoma consisted largely of fibroblastic cells and leiomyosarcoma cells were packed in forming small cell groups with constant junctional complexes of nexus and zonula adherens types. MFH showed variable cellular features containing the cells with myofibroblastic and histiocytic differentiation. Malignant schwannoma was characterized by tumor cells having slender cytoplasmic processes with overlapping or interdigitation and thick basement membrane. These ultrastructural features were contributory to the differential diagnosis of the sarcomas examined.

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

The diagnosis of malignant schwannoma may be difficult or impossible by light microscopy alone, if the neoplasm is poorly differentiated and if there is no clinical evidence for its arising from a nerve-trunk. Six cases of malignant schwannoma in which electron microscopy confirmed or established the diagnosis are reported. In four cases, the anatomic origin of the neoplasm arising from a large nerve was demonstrated at the time of operation, and in one of these the patient had von Recklinghausen's disease. In three of the four cases, as well as in the fifth case, in which the tumor was associated with an overlying malignant melanoma, the distinctive schwannoma patterns of Antoni types A and B tissue were absent. In the sixth case, there were no clinical clues as to nerve sheath origin, but both the light and electron microscopic features of the neoplasm were very characteristic of Schwann cell derivation. The most consistently present, ultrastructural features of malignant schwannoma are the spindle shape of the cells and the terminal cytoplasmic processes. If the processes show intertwining and if lateral cell borders are interdigitated, the diagnosis is more readily confirmed. Likewise, basal lamina is an important diagnostic feature but may be scant and focal in the very cellular and less differentiated tumors. Microfilaments are usually present, albeit in varying numbers, and they do not form the dense bodies seen in smooth muscle cells. Other diagnostically useful, but less consistent characteristics include microtubules, primary and secondary lysosomes, and dense-core type granules. Long-spacing collagen was present in only one case and in none of those reviewed from the literature. This is also an important finding. It is probable that most malignant nerve sheath neoplasms arise from Schwann cells, rather than from fibroblasts or perinurial cells, but electron microscopy often will be necessary to confirm this impression.

Spinal malignant schwannoma in a 5-year-old boy: ultrastructural evidence of its perineurial origin

A case of a malignant spinal schwannoma in a 5-year-old boy is reported. Electron microscopic findings permitting the classification of the tumor and its possible origin from the nerve sheath (perineurial cell) are discussed.

Neurosarcomatous transformation in malignant melanoma: an ultrastructural study

Six cases of desmoplastic melanoma were studied by light and electron microscopy. The tumors fulfilled one or more of the following criteria: (1) having the presence of atypical intraepidermal melanocytic proliferation bordering the primary lesions; (2) an antecedent history of melanoma at the site of recurrence; (3) a metastatic lesion in the direct lymphatic drainage route of a previously excised melanoma. Premelanosomes were not identified in the neoplastic cells. Ultrastructural features common to the six tumors were interpreted as evidence of Schwann cell differentiation, i.e., neurosarcomatous transformation occurring in malignant melanoma. The ultrastructural findings provide further support for the concept that melanocytic lesions may simulate tumors of Schwann cell origin, presumably reflecting the common embryologic origin of the two cell types from the neural crest.

Malignant neurogenic tumor of the heart

This is the first report of the fine structure of a malignant neurogenic tumor in the heart. The tumor, arising in the infundibulum of the right ventricle of the heart, was resected and examined by both light and electron microscopy. The histologic appearance of the originally resected tumor was consistent with that of a neurofibroma, while that of the recurrent tumor suggested a malignant schwannoma. Ultrastructurally, the presence of basement membrane investing some cells confirmed the neurogenic nature of the tumor. The discontinuous nature of the basement membrane in these cells may provide a clue as to the malignant nature of this tumor.

Malignant schwannomas presenting as malignant fibrous histiocytomas

Two soft tissue neoplasms considered to represent malignant fibrous histiocytomas by light microscopy showed typical findings indicative of Schwann cell origin when examined by electron microscopy. These findings included the presence of cells exhibiting long interdigitating cytoplasmic processes, which frequently contained collections of microtubules and were surrounded by thin, frequently interrupted, basal lamina material. In addition, pinocytotic activity at the cell surfaces and immature junctions joining apposing cellular membranes were identified. No evidence of fibroblastic, fibrohistiocytic, or myofibroblastic differentiation was identified ultrastructurally in the neoplastic cells. Our findings stress the need for ultrastructural examination to adequately classify soft tissue sarcomas. The 2 cases presented illustrate that there are some schwannomas that may be inaccurately classified as malignant fibrous histiocytomas if only light microscopy is used. It seems that only by ultrastructural means is it possible to accurately classify these peculiar neoplasms.

Peripheral nerve sheath tumors: an electron microscopic study of 43 cases

To obtain data concerning their histogenesis, 23 benign solitary schwannomas (including five cellular variants), 10 neurofibromas, and 10 malignant peripheral nerve sheath tumors were studied by electron microscopy. The results confirm previous findings that solitary schwannomas (so-called neurilemomas) are composed principally of cells showing features of differentiated Schwann cells. The principal cells of neurofibromas on the other hand did not resemble differentiated Schwann cells. The predominant cell type in six cases was indistinguishable from normal perineurial cells. Schwann cell-axon complexes seen in three cases may have represented entrapped normal structures or perhaps one component of a hamartomatous tumor. In contrast to the benign neoplasms the cells of the ten malignant peripheral nerve sheath tumors were in general poorly differentiated. When differentiated, they shared some features with Schwann and perineurial cells. Cell forms intermediate between them and fibroblastic cells were also identified. These findings indicate that schwannoma and neurofibroma are distinct entities. In the authors' experience schwannomas rarely undergo malignant change. For this reason and because it is unclear whether malignant tumors of peripheral nerves arise from more than one sheath cell, the designation of malignant peripheral nerve sheath tumor (PNST) is preferable to malignant schwannoma.

Neurogenic sarcomas of the neck in neurofibromatosis

Based on two observations and a review of the literature, the pathological and clinical findings in sarcomas of the neck in patients with neurofibromatosis are described. Histologically these neurogenic tumours show a manifold picture; in addition to spindle-cell sarcomas pleomorphic structures are to be found, which can be similar to rhabdomyo-, lipo-, chondro-, angio-, or osteogenic sarcomas so that a histological diagnosis of a neurogenic sarcoma cannot always be made without clinical details. Up to the present surgical treatment is preferred; the value of cytostatic therapy and irradiation is controversial. The results of treating these tumours are unsatisfactory. Of 29 cases reported in the literature, only two could be found in which the patient survived without a recurrence for more than five years.

Collagen synthesis in cells cultured from v. Recklinghausen's neurofibromatosis

Subcutaneous tumors of a patient with v. Recklinghausen's neurofibromatosis contained about 31% collagen calculated on the basis of lipid-free dry weight. Slices of the tumors synthesized collagen at a rate (4.7-8.5% from total protein) which was higher than that of the skin slices (2.8-5.9%). Neurofibromatosis cells were cultured from tumors of two patients. They synthesized relatively much more collagen than cultures of skin fibroblasts of the same patient or of healthy age-matched control persons. The second patient's cultures were studied in detail. The cell densities of these cultures were higher and expressed more variation than the densities of control skin fibroblasts. Ion exchange cellulose chromatograms, SDS-polyacrylamide gel electrophoresis and 3-hydroxyproline analysis of the radioactive proteins made by the cultures indicate that most of the collagenous proteins resembled type I collagen. High proliferative capacity and high collagen synthesis of selected neurofibromatosis cells explains the growth of solid tumors.

Malignant tumors of nerve sheath origin

A clinicopathologic study of malignant nerve sheath tumors diagnosed between 1962 and 1979 at the Massachusetts General Hospital was undertaken. During this 17-year period, 24 patients with such a neoplasm were seen while 607 patients were treated for schwannoma or neurofibroma. Criteria were developed for establishing the nerve sheath origin and malignancy of a given neoplasm which allowed a secure diagnosis of malignant nerve sheath tumor to be made in 11 of the 24 cases. In 7 of the remaining cases, the malignant tumors were of uncertain histogenesis and in 6 cases, a new diagnosis was made. The malignant tumors constituted 2% of all neoplasms of the nerve sheath origin diagnosed during this period. An attempt was made to grade these neoplasms, but clinical and histologic parameters were only approximately predictive of their behavior. The treatment and survival or the 11 patients with malignant nerve sheath tumors and the 7 with malignant neoplasms of uncertain histogenesis are detailed and compared. In the former group, 4 patients died within four and a half years and there were eight recurrences in 4 patients. In the latter group, 4 died within three and a half years and there were five recurrences in 3 patients.

Tactile-like structures in neurofibromas. An ultrastructural study

The light- and electron-microscopic features of four neurofibromas are described. In each case, whorled structures resembling tactile corpuscles were observed. Ultrastructurally, these lamellated formations were composed predominantly of perineurial cells, although many had a "central core" containing either a myelinated or unmyelinated axon, or several Schwann cells unassociated with axons. Our findings provide further evidence for the participation of perineurial cells as well as Schwann cells in the histogenesis of neurofibromas.

Scanning electron microscopy of in vitro grown cells from experimentally induced neurogenic tumors

Serially transplanted neurogenic tumors of experimental origin were explanted in vitro and analyzed by scanning electron microscopy. In explants of intracerebrally transplanted gliomas, small stellate cells with branching processes were observed; in transplanted tumors of the peripheral nervous system, slender bipolar cells as well as fibroblasts emerged. The stereoscopic features were compared with the picture of conventional light microscopy. The findings are consistent with the assumption of the glial derivation of CNS-tumors induced with neurotropic alkylating carcinogens. The peripheral tumors are composed of Schwann-cell like elements and fibroblasts. The significance of the results for the cytogenetic derivation of brain tumors are discussed.

A nonfunctioning paraganglioma of vagus nerve: an ultrastructural study

The clinical, histological, and ultrastructural aspects of a cervical paraganglioma of the vagus nerve, in a 66-year-old white man, have been discussed in detail. Ultrastructurally, the tumor chief cells contained characteristic membrane-bound and dense-cored neurosecretory granules which ranged in size from 85 millimicron to 190 millimicron. Unlike earlier ultrastructural reports, the present study showed the presence of sustentacular or supporting cells. These cells were smaller, darker, polymorphic, and were commonly located at the periphery of a single or group of chief cells. Furthermore, unlike earlier reports on vagal paragangliomas, nonmyelinated nerve fibers and an occasional axon were identified in the present fine structure study.

Benign nerve sheath myxoma: light and electron microscopic features of two cases

Two new cases of the rare benign nerve sheath myxoma (NSM) are presented. The light microscopic findings are compared with previously reported cases. In addition, the ultrastructural features of three constitutent cell types are described. The lesion is confirmed as a neural sheath neoplasm, and its similarities to other myxomas are discussed.

Ultrastructural identification of a benign perineurial cell tumor

A solitary tumor which by light microscopy was calssified as a neurofibroma was found by electron microscopic study to be composed of parallel, elongate cells with collagen rich intervening matrix. The cells showed thin, polar cytoplasmic processes which extended long distances, frequent junctional complexes between cell processes, numerous surface vesicles, and either no or fragmented and variable basement membrane. Perineurial cells from small peripheral nerves of skin were demonstrated to have similar morphologic characteristics as the tumor cells. The present study, together with previous ultrastructural findings, indicate that benign peripheral nerve sheath tumors should be placed in at least three categories: Schwannoma, neurofibroma and perineurioma.

The ultrastructure of bovine peripheral nerve sheath tumours

Bovine peripheral nerve sheath tumours from 30 cattle were similar ultrastructurally to human schwannomas and neurofibromas. Bovine neurofibromatous tissue had large amounts of extracellular material, primarily collagen and electron lucent granular material. The principal cells had basal laminae and a disorganized proliferation of the plasmalemma. Axons were consistently seen and were surrounded by the plasmalemma of principal cells. The principal cells seemed to be Schwann cells or variants of them. Bovine schwannomas had areas similar to Antoni type A tissue with sparse extracellular material, few, if any, axons, and an apparent organized layering of cytoplasmic processes clad in a basal lamina. Cell nuclei often formed palisades. The principal cells in bovine schwannomas might be derived either from Schwann cells or perinuerial cells. Bovine schwannomas appeared together with bovine neurofibromatous tissue in affected nerves.

Bovine normal peripheral nerve and nerve sheath tumour in explant culture

When bovine normal nerve and nerve sheath tumours were cultured using explant techniques, the same morphological cell types were seen:thin bipolar cells with bulging nuclei;found refractile cells; large quadrangular cells; variable polar, wide-processed cells. However, differences in the pattern of cell growth and the proportions of morphological cell types occurred between normal and tumour nerve. The bovine nerve sheath tumours cultured showed a range of histological areas which did not appear to affect the pattern of cell growth in culture or the cell types present. Antoni type A tissue was prominent in many explant blocks and probably gave rise to most cell growth. On comparison with human schwannomas maintained in explant culture, bovine nerve sheath tumours appeared to have a similar range of morphological cell types. Although suggestions for the origin of human schwannomas have been made on the basis of cell morphology, it was felt that morphology alone did not allow speculation on the origin of cells present in bovine nerve sheath tumour explant cell growth.