Studies on experimental malignant nerve sheath tumors maintained in tissue and organ culture systems. III. Melanin pigment and melanogenesis in experimental neurogenic tumors: a reappraisal of the histogenesis of pigmented nerve sheath tumors

Malignant neuroectodermal tumor with melanocytic and rhabdomyoblastic differentiation

Malignant melanoma can metastasize widely and vary significantly in its histological appearance; it rarely presents as a deep-seated mass without an obvious primary site elsewhere. Malignant peripheral nerve sheath tumor (MPNST) is a high-grade sarcoma characterized by conventional and epithelioid subtypes. MPNST can demonstrate heterologous differentiation, usually in the form of osteosarcomatous, chondrosarcomatous, or rhabdomyosarcomatous differentiation. MPNST does not harbor true melanocytic differentiation, although epithelioid MPNST typically is diffusely S-100 protein positive and superficially can resemble malignant melanoma. An unusual intra-abdominal mass was recently encountered with features of both melanoma and conventional or epithelioid MPNST containing a fascicular spindle cell component, an epithelioid component with melanocytic differentiation, as well as a rhabdomyosarcomatous component. The terminology “malignant neuroectodermal tumor with melanocytic and rhabdomyoblastic differentiation” is proposed to describe this neoplasm, reflecting the unusual concomittant lines of differentiation as well as offering a possible rationale for nosologically challenging aspects of this neoplasm.

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.

Intradermal melanocytic nevus with prominent schwannian differentiation

Features of peripheral nerve sheath differentiation such as neuroid cords, nerve corpuscles, fascicle-like structures, and, exceptionally, palisading have been reported in melanocytic nevi. We report an intradermal melanocytic nevus with prominent Verocay-like bodies. The upper portion of the neoplasm was composed of typical round intradermal nevus cells, many of which were pigmented. Within the deeper portion, there was a nonpigmented spindle cell proliferation with prominent Verocay bodies, simulating a neurilemmoma. Typical nevus nests merged with neurilemmoma-like areas. The entire lesion stained positively for S-100 and Mart-1 proteins and negatively for HMB-45 stain. Diffuse Mart-1 positivity excluded a collision of a melanocytic lesion with a neurilemmoma. The histopathologic features of this nevus further support a close relation between nevus cells and Schwann cells.

Pathology and incidence of amelanotic melanomas of the skin in F-344/N rats

A total of 121 spontaneous amelanotic melanomas of the skin were identified in 70 of 11,171 male and 51 of 10,927 female Fischer-344/N rats in 63 2-yr carcinogenicity studies conducted by the National Cancer Institute's Carcinogenicity Testing Program/National Toxicology Program. Amelanotic melanomas had characteristic anatomical locations and histologic features distinguishable from Schwann cell tumors. Of the 121 tumors, 84, 19, 10, and 8 cases occurred in the pinna, eyelid, scrotum, and perianal region (anus and tail), respectively. Amelanotic melanomas originated from the dermis and consisted of spindle cells arranged in an interlacing fascicular pattern often with a perivascular orientation; epithelioid cells were rarely seen. Only the tumors arising in the pinna metastasized to the lung and/or mandibular lymph nodes. The metastatic rate was 19% (16/84) of the tumors and was clearly increased with an increase in tumor size. Most metastasizing tumors had focal areas consisting of anaplastic spindle cells with an increased number of mitosis. The tumor cells stained positive for S-100 protein but negative for melanin. Ultrastructurally, the tumors were diagnosed as amelanotic melanomas based on the identification of numerous, intracytoplasmic premelanosomes without melanin formation in the tumor cells which were not enveloped by pericytoplasmic basal laminae. One localized amelanotic melanoma of the pinna was successfully transplanted to the subcutaneous tissue in the flank of 3 Fischer-344/N rats.

Malignant schwannoma with rhabdomyoblastic and melanocytic differentiation

This is the first case report of an unusual malignant tumor with components of malignant schwannoma, rhabdomyosarcoma, and melanoma, occurring in an adult. The tumor was observed in the left temple in a 35-year-old man without von Recklinghausen's disease. The possible derivation of this tumor from primitive neuroectodermal cells is discussed.

Intraspinal pigmented schwannoma with malignant progression

A case with recurrent pigmented intraspinal tumour with malignant progression is presented. The primary tumour grew around the nerve roots T9 and T10, was attached to dura and infiltrated the vertebral bone tissue. On light microscopy it was comprised of monomorphic cells with large amount of cytoplasmic pigment and many large pigmented globoid bodies. Mitoses were not observed. On electron microscopy, in addition to cytoplasmic melanosomes of regular size, macromelanosomes were numerous. The tumour cells were surrounded partially by basement membrane like material. On these bases a histological diagnosis of benign pigmented tumour of neural crest origin was suggested (a possible pigmented meningioma or pigmented schwannoma). The patient got a recurrence one year after the primary operation. Biopsy from the re-operation showed histologically the same type of tumour with more pleomorphic cells. Subsequently, the tumour grew progressively and metastases were observed in the lungs and in the skin. The patient died two years after the primary operation. The malignant progression of the tumour and other reports on similar tumours was most consistent with a diagnosis of malignant pigmented schwannoma and this was confirmed later on with immunohistochemical staining showing positive staining for basement membrane components, collagen type IV and laminin as well as a positive staining for S-100 protein. The present findings show that despite benign histological features these tumours can behave very aggressively and stress the need of more information on this type of tumour.

Uveal malignant melanoma and von Recklinghausen's neurofibromatosis

A case of uveal malignant melanoma with extensive spread to the central nervous system occurring in a 63-year-old woman with peripheral-type von Recklinghausen's neurofibromatosis was studied by light microscopy. The tumor histologically consisted of large, loosely coherent epithelioid cells with abundant eosinophilic cytoplasm and large, irregular nuclei with prominent nucleoli. The tumor cells contained variable amounts of melanin pigment and exhibited positive immunohistochemical staining for S-100 protein and neuron-specific enolase. A review of the literature disclosed only ten previous cases of uveal malignant melanoma associated with von Recklinghausen's neurofibromatosis. A predominance of women and of the peripheral variant of von Recklinghausen's neurofibromatosis was noticed in the cases reported.

Melanin-forming Schwann cells in some oral mucosal lesions

Normal oral mucosa and some mucosal lesions show melanin pigmentation, and it is usually assumed that melanin-containing cells in the lamina propria are melanophages. In a study of oral mucosa from two cases of lichen planus and tow of sublingual keratosis, many brown, intracellular, Masson-Fontana-positive granules were seen. At the ultrastructural level some of the melanin-containing cells displayed characteristics of Schwann cells rather than melanophages. These cells were surrounded by a basal lamina and contained unmyelinated axons. Although the majority of the melanin granules in these cells were compound melanosomes, single melanosomes and premelanosomes were also seen. These findings show that in sublingual keratosis and oral lichen planus lesions some of the melanin-containing cells in the connective tissue may be melanin-forming Schwann cells.

Induction of malignant peripheral nerve sheath tumors in European hamsters with 1,1-dimethylhydrazine (UDMH)

A rate of up to 43% of malignant peripheral nerve sheath tumors (PNST) was induced in European hamsters (EH) after weekly s.c. administration of 1,1-dimethylhydrazine (UDMH). The overall neoplastic response in the treated EH was also elevated as compared to the untreated controls. Histologically, the malignant PNST were neurofibrosarcomas and melanotic as well as unpigmented schwannomas. The occurrence of melanotic schwannomas is briefly discussed with regard to the histogenesis of this rare tumor type.

Reversible endoneurial changes after nerve injury

Endoneurial changes in the rat sciatic nerve were studied during Wallerian degeneration and subsequent regeneration. After total axotomy two different experimental models were used. In the first the cut ends of the sciatic nerves were left free to allow reinnervation. In the second model the distal end of the transected nerve was sutured to the adjoining muscle to prevent regeneration. Within 2 weeks after the axomoty, a Wallerian type of degeneration was seen with axonal destruction and phagocytosis of myelin sheaths. After 4 weeks endoneurial fibroblastic cells formed circular structures around the Schwann cell columns, i.e., the bands of Buengner in both groups. These fascicle-like structures became more pronounced in the non-regenerating nerves up to 8 weeks, while during reinnervation the cellular reaction in the endoneurium nearly disappeared within this time. Ultrastructurally, the endoneurial fibroblast-like cells showed marked phagocytotic activity and also fragments of basement membrane on their surface. The appearance of thin (25-30 nm in diameter) collagen fibrils closely related to the basement membrane was noted around the bands of Buengner, as well as the appearance of an amorphous extracellular gap between the newly synthetized thin collagen fibrils and normal endoneurial collagen (50-60 nm). The reversible endoneurial compartmentation seems to be important for maintaining the nerve structure, serving as a support for axonal regeneration in addition to the bands of Buengner.

Melanotic neurofibroma: a case report with ultrastructural study

The authors report a case of a solitary melanotic neurofibroma involving the temporomalar area in a 17-year-old man. Light-microscopic study reveals a benign neurofibroma including melanin deposits. Electron microscopy shows typical premelanosomes and melanosomes within Schwann cell cytoplasm. The literature is reviewed, and theories of histogenesis for this unusual tumor are discussed.

Malignant melanoma of the sympathetic chain: with a consideration of pigmented nerve sheath tumours

A case of malignant melanoma of the posterior mediastinum, arising from the sympathetic chain is reported. The structural features and the presence of long-spaced collagen on electron microscopic examination suggest schwannian derivation of the tumour. Similar tumours are reviewed and the histogenesis of pigmented nerve sheath tumours in general is discussed. The term 'malignant melanotic schwannoma' is probably the most appropriate for the tumour entity described here.

Primary melanocytic schwannoma of the stomach. Evidence of dual melanocytic and schwannian differentiation in an extra-axial site in a patient without neurofibromatosis

Pigmented neoplasms of the peripheral nervous system are uncommon. Such lesions, while well documented in the para-axial region, are infrequently encountered in more peripheral extra-axial sites. The authors present a case of a melanocytic schwannoma arising in the gastric antrum of a 51-year-old woman. Ultrastructural features attesting to the nerve sheath origin of the neoplasm included the presence of a well-developed basal lamina, complex infoldings of the plasma membrane, and intercellular bundles of long spaced collagen ("Luse bodies"). Premelanosomes and melanosomes in all stages of development were identified within the cytoplasm of many of the neoplastic cells, providing morphologic support for a close relationship between Schwann cells and melanocytes. Immunoperoxidase studies with S-100 protein disclosed intense cytoplasmic staining throughout the tumor. The S-100 protein antigen has been documented in both nerve sheath elements and melanocytes; this shared antigenicity lends further support to the close relationship between melanocytic and schwannian elements suggested by ultrastructural observations. Additional immunoperoxidase studies employing antibody to glial fibrillary acidic protein revealed focal cytoplasmic staining, an uncommon phenomenon in peripheral nerve sheath neoplasms. A review of the literature failed to provide any previous well documented cases of melanocytic schwannoma of the stomach. The patient was treated with en bloc resection of the tumor and gastric antrum, and was free of evidence of recurrent or metastatic disease 22 months postoperatively. Theories regarding the histogenesis of pigmented nerve sheath neoplasms and prognostic implications are discussed, based on experience with this and previously reported pigmented nerve sheath tumors.

Meningeal melanocytoma of Meckel's cave associated with ipsilateral Ota's nevus

A case of meningeal melanocytoma of the left Meckel's cave associated with ipsilateral Ota's nevus in a 43-year-old woman, was studied by light and electron microscopy. The cells of the tumor were characterized by the presence of dendritic cytoplasmic processes, melanosomes and premelanosomes; hence, they were deemed as neoplastic melanocytes. Moreover, the tumor was lacking in histologic and ultrastructural features of pigmented meningioma, melanotic Schwannoma and primary meningeal melanoma. The prolonged clinical course was different from primary and metastatic malignant melanomas of the meninges. The best treatment appears to be radical excision, when possible; otherwise, the local or partial enucleation followed by radiation therapy has been found to be the best curative to date. On the whole, meningeal melanocytoma cannot be considered as entirely benign, given its morphologic patterns that resemble those of uveal melanoma, and its potential for recurrence. The association of this tumor with Ota's nevus is referred to as having a common origin from an arrested migration of melanoblasts at different stages.

Melanin production in a medullary thyroid carcinoma

Melanin production by a medullary thyroid carcinoma (MTC) is reported and discussed. Immunohistochemically, the tumor cells contained calcitonin; by electron microscopy, they bore numerous, heterogeneous granules similar to those described previously in MTCs. One small focus of tumor was pigmented. Here, melanosomes in different stages of maturation were found in dendritic cells that ramified among granule-bearing cells. The remarkable phenotypic divergence in this solitary, nongerm cell neoplasm is unusual but not so surprising in light of the APUD nature and neural crest origin of both the melanocyte and the thyroid C cell, which gives rise to MTC. The authors view the calcitonin and melanosome phenotypes as closely related tumor clones evolving from a common precursor neoplastic cell. This unique "experiment of nature" adds to the set of rare human tumors that make melanin "ectopically."

Pigmented olfactory neuroblastoma: a new example of melanotic neuroepithelial neoplasm

The light and electron microscopic features of a pigmented olfactory neuroblastoma are described. The neuroblastic nature of the tumor was confirmed by the demonstration of axons, some of which originated from the neoplastic cells, and by the presence of dense-core vesicles in the perikarya and processes of the tumor cells. The tumor contained a large amount of pigment, most of which had the histochemical reactions of melanin, but some of which had that of lipofuscin. Electron microscopy failed to demonstrate the presence of melanosomes or premelanosomes: the pigment showed some of the features of neuromelanin, although the fine structural appearances were not typical. The pigment was interpreted in this case as presumably representing a modified catecholamine degradation product, perhaps related to lipofuscin. The presence of melanotic pigment in an example of olfactory neuroblastoma, unreported until now, augments the list of neurogenic neoplasms in which an association with melanin formation has been described. The significance of this association in tumors originating from the nervous system or its coverings needs further investigation, as the nature of pigment appears to be heterogeneous. These tumors may contain either melanosomal pigment or pigment identified as neuromelanin (or a related substance), seemingly regardless of the derivation of the pigment-bearing cells.

Spinal melanotic clear-cell sarcoma: a light and electron microscopic study

We report a melanotic spindle-cell tumor that arose from a thoracic spinal nerve root and metastasized to both lungs. The bulk of the tumor consisted of glycogen-rich clear cells and bore a striking resemblance on light and electron microscopy to at least one variant of the clear-cell sarcoma of tendons and aponeuroses. The presence of schwannoma-like areas noted in the primary tumor on light microscopy and the formation of a highly developed basal lamina noted on ultrastructural examination suggest that the tumor may be a partially dedifferentiated malignant melanotic schwannoma. This tumor is discussed in the context of a simple histogenetic classification of melanotic tumors.

Pigmented storiform neurofibroma

A case of pigmented storiform neurofibroma (PSN) is presented. The lesion was present in the shoulder of a 7-year-old black girl and recurred after 10 years. The characteristic storiform pattern and melanin production are the relevant features for histologic diagnosis. The histogenesis and taxonomic position of this lesion is discussed with emphasis on its relationship with dermatofibrosarcoma protuberans (DFSP) and cellular blue nervus.

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

Explants from seven nerve sheath tumors (four cranial and three spinal) induced in rats by transplacental ethylnitrosourea were grown on collagen-coated coverslips and in organ culture systems, using sponge foam matrices and Millipore filter platforms. Their sequential morphological features in vitro were compared to those of a human acoustic Schwannoma maintained in similar culture systems. The original experimental tumors were either undifferentiated or poorly malignant Schwannomas. In cultures on collagen-coated coverslips the explants demonstrated cellular features that were considerably more anaplastic than those of the human acoustic Schwannoma. On the other hand, in organ culture systems, in which viable cultures were maintained up to 82 days, many of the experimental tumor explants exhibited progressive differentiaiton, with nuclear palisading, increasing whorl formation and abundant reticulin fibers, and their pattern of histological organization came therefore closely to resemble that of the cultured acoustic Schwannoma. Unlike the latter, however, the cultured experimental tumors infiltrated the sponge foam matrices, a feature that mimicked the invasive character of the original tumors in vivo. Included normal ganglion cells remained demonstrable in the cultures up to 69 in vitro.

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

The sequential electron microscopic features of six malignant nerve sheath tumors (three cranial and three spinal) induced in rats by transplacental ethylnitrosourea and maintained in organ culture systems were compared with those of a human acoustic Schwannoma similarly cultured. After 4 weeks in vitro, the malignant tumor cells often showed progressive elongation of their processes, with the development of an interdigitating pattern resembling that seen in well-differentiated Schwannomas. This was accompanied by an increase of microtubules. Basal lamina formation, less well-developed and less complete than in the benign Schwannoma in this study, was maintained in culture. Some explants demonstrated an increase in number and width of collagen fibrils, accompanied by a relative concomitant decrease of inter-cellular basement membrane material. The malignant tumor cells also showed numerous micropinocytotic vesicles and various junctional complexes, which are characteristic of perineurial cells. Since the origin of the experimental tumors from adult Schwann cells seems well established, this apparent contradiction is best resolved by the concept that Schwann cells and perineurial fibroblasts are functional variants of the same cell type.