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The "gliogenic" participation in the edification of granulomas may produce peculiar morphological features especially in the central nervous system, and perhaps more than elsewhere, pseudotumoral features. Moreover, the concept of "granuloma" is perhaps not as well defined as in the other tissues. There are also some still unsolved problems concerning the histogenesis of the cells of the "granuloma". Some examples taken among the different etiologies illustrate these notions.

Two familial and sporadic cases of amyloid neuropathy are reported. Nerve biopsies ultrastructural studies permit to involve endothelial and Schwann cells basement membranes into formation of amyloid. This classical notion was worth being recalled and specified. The purpose of amyloid formation is searched in a toxico-metabolic processus possibly in relation with observed demyelinating mechanism. The Schwann cell is at the cross of the cause and of its effect.

The authors describe an anatomical familial case of progressive infantile cerebral poliodystrophy (Alpers disease), in which the study of enzyme kinetics of hepatic pyruvate carboxylase revealed an abnormal graph reflecting a loss of activity of the enzyme with low concentrations of substrate, This is a new feature in the literature on Alpers disease, and possibly indicates one of the pathogenic mechanisms responsible in this disorder which remains mysterious, although its pathology has been clearly described.

The authors review 500 extemporaneous histopathological examinations done in a neurosurgical unit over a 16-month period. The following four questions are asked by the neurosurgeon: is there a tumor? is it a primary or secondary one? what variety is it? what is its degree of malignancy? The percentage of errors was respectively: 2 per cent, 2.2 per cent, 8.8 per cent and 7.4 per cent, or roughly, a percentage two times lower than in a series from the same laboratory done before the use of the low-temperature microtome. It especially seems that the tumoral variety is often determined accurately in meningiomas, neurinomas, medulloblastomas and craniopharyngiomas. In gliomas the variety is often more difficult to accurately affirm, and especially the "grade" of malignancy. The authors analyse the problems raised by the different types of tumors.