Malignant schwannoma: a light microscopic and ultrastructural study

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.

Pathologic features of nerve sheath tumors with respect to prognostic signs

Clinicopathologic evaluation of primary and recurrent nerve sheath tumors was performed for 87 fully documented cases treated in the National Oncological Institute (Budapest) between 1955 and 1976. Morphologic features of all tumors, i.e., of both nonrecurring and recurring tumors with and without malignant transformation, were evaluated according to a uniform scoring system. Scores of the primary tumors showed good correlation with their further course; in case of recurring tumors, the scores permitted some conclusions regarding their expectable behavior. Neurofibromas and neurinomas displayed similar courses, but the clinical courses of typical and cellular tumors were not the same. Cellular tumors with high scores were more disposed to recur and undergo malignant transformation. Recurrences in cases of late malignant transformation were more frequent than in those showing no transformation.

Evidence supporting neural crest origin of an alveolar soft part sarcoma: an ultrastructural study

A case of an alveolar soft part sarcoma was studied electron microscopically. This showed tumor cells separated by external lamina that incorporated desmosome-like structures. Well defined basal lamina separated several cells from underlying endothelial cells by a zone of tissue composed predominantly of fibrous long-spacing collagen. A unique finding was the presence within several tumor cells of well defined myelin sheaths and myelinated axons. Apart from various other intracellular organelles some of the cells contained closely aggregated fine filamentous structures: the so-called "angulate bodies." All these findings are interpreted as evidence for a tumor showing marked Schwann cell differentiation, and therefore, it is suggested that alveolar soft part sarcoma is histogenetically a neoplasm of the neural crest.

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.

Malignant transformation of intrathoracic ancient neurilemoma in a patient without von Recklinghausen's disease

A case of intrathoracic ancient neurilemoma undergoing malignant change in a 48-year-old woman is reported. The lesion was first discovered incidentally during routine roentgenologic examination of the chest 15 years before its surgical removal. The gross and histologic examination of the tumor showed the features of ancient neurilemoma with extensive regressive changes as well as small preserved areas composed of Antoni type A and B tissues. In addition, obviously histologically malignant foci manifested by the presence of increased cellularity, active mitotic activity, and gradual loss of orginary neurilemomatous differentiation were present. The patient died 16 months after operation of recurrent and distant metastatic disease. At autopsy, there was no evidence of generalized neurofibromatosis or other primary cancer. A review of the available literature revealed only two other similar cases documenting malignant transformation of solitary benign neurilemomas in patienets without von Recklinghausen's disease.

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.

Electron microscopy in the diagnosis of malignant schwannoma

Fifteen malignant schwannomas were examined by light and electron microscopy. Five tumors arose in patients with neurofibromatosis and five were contiguous with a peripheral nerve (Group I). Five tumors met neither of these generally accepted diagnostic criteria but were light microscopically seen as compatible with malignant schwannoma when examined under light microscope (Group II). In the better differentiated areas of Group I lesions, long, overlapping, tightly packed cytoplasmic processes were parallel to homogeneous flocculent material, occasionally assuming a linear appearance suggesting basal lamina. In Group II, similar cytoplasmic processes were present but the extracellular material was less extensive and had a less obvious relationship to the plasma membrane. In neither group were fine intracytoplasmic filaments prominent. Malignant schwann cells are seldom as ultrastructurally differentiated as their benign counterparts. Nevertheless, within the context of well-studied light microscopy and the sampling error inherent in ultrastructural examination, electron microscopy can support the diagnosis of malignant schwannoma.