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This report presents the ultrastructural study of a germinoma of the third ventricle occurring in a 13 year old boy. The electron microscopic data showed similarities linking this tumor to gonadal and mediastinal germinomas and emphasized the exceptional glycogenic storage in tumor and stroma cells. Another morphological analogy was the intense macrophagic activity that led to tumor cell phagocytosis. The authors discuss the meaning of such an immune response, which is usually not observed in cerebral tumors.

The authors comment on the role of electron microscopy in the diagnosis of brain tumors. This kind of morphological investigation is essential for the differential diagnosis of undifferentiated or round cell tumors, especially on small biopsies. In addition, electron microscopy clarifies the nosology of numerous entities, such as germinomas, lymphomas, astrocytic gliomas, neuronal tumors, medulloblastomas and pinealomas. Finally numerous ultrastructural details are provided, widening our knowledge of the complex pattern of brain tumors.

An unusual cerebral tumor is reported in a ten-month-old boy. The tumor was large (10 cm x 6 cm), firm and included several cysts. Light and electron microscopy showed a striking cellular pleomorphism. Typical neurosecretory ganglion cells were observed, always surrounded by Schwann cells. Amyelinic neurites, clusters of Schwann cells, fibroblasts and numerous foci of GFA positive astrocytes composed the tumor. These features were compared with the rare previous electron microscopic reports of cerebral neuronal tumor of the central nervous system. A dysembryoplastic origin from the neural plate was retained to explain the growth of such a complex tumor.

Twenty-three cases of primary brain lymphomas were morphologically studied. Electron microscopy was done in twelve cases and immunoperoxidase reactions for light chains of immunoglobulins in ten cases. The patients were fourteen males and nine females. Except two children, the mean age was 50 years. Clinical features and pre-operative investigations lacked any specificity. Post-operative radiotherapy could be performed in thirteen patients, eleven of them being still alive with a follow-up varying from 2,5 months to 4,5 years. All the other patients persued fulminating course (max: 4,5 months). Tumors were preferentially located in frontal and temporal lobes. On gross examination, well limited tumors were more frequent than ill-defined or purely infiltrating tumors. Microscopically, all the lymphomas were of the diffuse type. Perivascular clusters of lymphoma cells, meningeal and parenchymal infiltrates and sub-ependymal sprouts were found in the peritumoral areas. The lymphomas were cytologically characterized according to the modified Kiel classification (Lennert et al, 1975) using light and electron microscopic data. So were identified thirteen lymphoblastic lymphomas (with one convoluted-cell type), one centroblastic lymphoma, eight immunoblastic lymphomas (two with plasmacytic differentiation). Light chains of human immunoglobulins were immunocytologically demonstrated in six of twelve tumors tested, all the positive cases corresponding to immunoblastic lymphomas. A unique case of primary meningeal Hodgkin's disease was found. These results were compared with the rare previous reports associating these different morphological investigations.

An ultrastructural study of four pinealomas was carried out to precise eventual specific markers. Dark and clear cells joined with zonulae adherents, extensive and pleiomorphous processes, a complex vacuolar system, and characteristic organelles (lysosome-like structures, clear and dense-core vesicles, vesicle-crowned rodlets and related structures, microtubular sheaves and centriolar derivatives, membranous whorls, fibrous bodies, microtubules, heterogeneous cytoplasmic inclusions) offered a typical pattern. No correlation could be made between the histological and ultrastructural features. The authors stress the ultrastructural similarities between the human tumor cells and the mammalian pineal cells. Pinealomas appeared as a morphological entity distinct from neuronal and astrocytic tumors.

The authors report electron-microscopic observations upon a primitive cerebral haemangiopericytoma. The vascular appearance of the tumour is due to the presence of abundant extracellular material which has a structure like that of vascular basement membranes. The fact that the tumour cells are pericytes is confirmed by the existence of intracytoplasmic microfilaments of 60-80 A in diameter, sometimes gathered into osmiophilic aggregations and forming simple cellular junctions (zonulae adherentes). Stress is laid upon the importance of differentiating this rare tumour from an angioblastic meningioma; the haemangiopericytoma is more rapidly growing and carries a more serious prognosis.

An ultrastructural study was performed on normal and Benzo(a)-pyrene(B(a)P)-transformed fetal mouse brain cells. Early subcultures of a strain initiated from whole brain presented three cell types in vitro: astroglial, poorly differentiated glial, and spongioblastic types. After B(a)P-treatment, there was an exclusive transformation and the growth of neuroglia sometimes without gliofibrillary maturation, but with the presence of glial fibrillary acidic protein (GFAP) in the cytoplasm. Early subcultures of another strain initiated from cortex only presented poorly differentiated neuroglial cells. After transformation, cell maturation as evidenced by gliofibrillogenesis and GFAP production by these cells was observed. In both cases, the potentiality of glial differentiation after in vitro malignant transformation by a chemical carcinogen seemed preserved.

The existence of an immunological blood-brain barrier (BBB) is well established but its role in cerebral tumour immunology is less well defined. Attempting to clarify this problem we tested the graft rejection of polyoma virus-induced central nervous (CNS) tumours in hamsters after systemic or intracerebral immunization with polyoma virus. Animals were immunized by intracerebral or subcutaneous inoculations of polyoma virus before tumours were induced by intracerebral or intramuscular graft of polyoma-transformed hamster neuroglial cells. The growth of cerebral and muscular tumours was significantly inhibited in animals immunized subcutaneously. In animals immunized intracerebrally the inhibition of growth was highly significant for cerebral tumours and only very slight for intramuscular tumours. These results suggest that the blood-brain barrier allowed immunocompetent effector cells to penetrate inside the CNS but prevented the locally elicited cell-mediated immune response from diffusing outside the CNS. The ability of the brain to develop a local immune response and the partial lack of circulation of immunocompetent cells to cross the BBB could be mainly responsible for the special immune status of the CNS and may greatly interfere with the establishment of an efficient immune response toward brain tumours.

The authors report seven cases of intracerebral germinomas studied on autopsy and/or biopsy material. Electron microscopy was done in five cases. Tumors were located on the middle line of the brain (pineal area, suprasellar region, third ventricle). Light microscopic features were stereotyped with PAS + round tumor cells and inflammatory mononuclear cells. By electron microscopy, fenestrated nucleoli, glycogen storage and annulate lamellae were always found, as well as a striking macrophagic activity of histiocytes. This immune reaction is supposed to contribute to the relatively favorable prognosis of these original brain tumors.

Paired twisted filaments (PTF) forming helices are described in tumor cells of three human pinealomas. Each filament was 8.11 +/- 1.55 nm wide. The maximal width of the helix was 16.62 +/- 2.62 nm. The periodicity of the constrictions was 26.63 +/- 4.49 nm. These characteristics appeared original, suggesting protein filaments possibly specific of pinealocytes. The similarities and discrepancies between PTF and Alzheimer's paired helical filaments (PHF) are discussed.