[Epithelioid cell-node induced by intracisternal injection of kaolin in rats]

We studied the origin of the epithelioid cells (macrophages) observed in the rat brain in response to the intracisternal injection of kaolin. The rats, two days of age, were used. The animals were killed after thirteen weeks following cisternal injection of kaolin. Massive epithelioid cell-nodes with multifocal necrosis were seen in the subarachnoid space of the cerebellum, in the cerebellar parenchyma and in the fourth ventricle. They were also present in the choroid plexus. The papillary epithelioid cell-nodes were observed onto the aqueduct of Sylvius, the third and lateral ventricles. These were associated with the proliferation of the adventitia of the blood vessel in the subependymal white matter. This suggested that the vascular adventitia played a role for a formation of the epithelioid cell-node in this case. The epithelioid cell was negative in silver-stained preparation. This indicated that microglia was not a source of the epithelioid cell. Reticulin fibers were moderately increased in the lesions. The epithelioid cells phagocytized kaolin granules and gave a strong PAS-positive reaction. However, it seemed that the PAS-positive materials were not identical to the kaolin granules. A rich accumulation of apparently extra- and intracellular kaolin deposits stained metachromatically violet with toluidine blue was seen in the necrotic areas. A large number of the degenerated cells containing kaolin deposits was found especially in the marginal zone of the necrotic areas. Granulation tissue with the amount of spindle-form cells and collagen fibers was also observed in the subarachnoid space. The granulation tissue was formed by hyperplasia of fibroblasts following the proliferation of the epithelioid cells and their necrotic processes.(ABSTRACT TRUNCATED AT 250 WORDS)