Primary actinomycoma of the third ventricle--the colloid cyst. A histochemical and ultrastructural study.

Primary actinomycoma of the third ventricle has been reported to be a very rare form of central nervous system actinomycosis. Others have demonstrated actinomycotic-like colonies in colloid cysts of the third ventricle. We have confirmed these structures (HLS) in five colloid cysts and have demonstrated by various histochemical stains that they consist of desoxyribose nucleic acid, base protein and phospholipid. Ultrastructurally, they consist of amorphous to granular electron dense material, probably deposited on a lamellar substructure. On the basis of the available information, we believe that the lesions, previously reported as primary actinomycomas, are actually colloid cysts containing degenerative HLS. The possible origin of the hyphal-like structures is discussed.