Fig. 3.19. a Dry keratin appears as parallel lines expanding into hexagonal plates depending on the plane of section. NP3880, H&E. b Wet keratin appears as swollen cells with ghosts of nuclei in a craniopharyngioma. NP-02-286, H&E.

more when it invades the dura, or when there is an excessive reaction in the connective tissue portion of the vascular components. Fibrous scar formation is almost always found in cases with previous surgical intervention. Irradiation also induces excessive proliferation of connective tissue. The differentiation from a sarcoma or a mixed glio-sarcoma is difficult unless one can demonstrate neoplastic features in the connective tissue, i.e. mitoses and numerous cycling nuclei in addition to the pleomorphism frequently seen in actively reacting fibrous tissue.

Terminology may be deleted with experience, and the "cerebellar sarcoma" - so diagnosed decades ago because of its rich fibrous connective tissue dividing the tumor into nodules (Fig. 3.20a) - is now known to be a desmoplastic medulloblastoma, but the prognosis remains the same with CSF metastases (Fig. 3.20b, c), just as in other medulloblastomas. Terminology also increases, of course, and both desmoplastic infantile ganglioglioma (DIG) and desmoplastic cerebral astrocytoma of infancy (DCAI) occur in the superficial cerebrum of infants, are rich in collagenous tissue, and tend to have a relatively favorable prognosis.

Inflammation Mild focal perivascular lympho-cytic cuffs are common but non-specific in many gliomas and other tumors. Pre-operative diagnostic procedures such as angiography may contribute to a mild inflammation. Foci of neu-trophilic reaction are occasionally seen in glioblastomas, causing differential diagnostic problems with other causes of necrosis or inflammation, especially when the specimen is inadequate. Lymphocytes of various types constitute the small cells of germinomas and become of diagnostic importance.

Hemorrhages, Old and Recent Evidences of recent and old hemorrhages may follow various treatments but also occur spontaneously in

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