Tubular (acinar) transformation of the choroid plexus epithelium.

The choroid plexus in the normal state shows a beautiful papillary (or villous) architecture supported by the intricately ramifying, thin fibrovascular stroma. This configuration is retained in benign and malignant neoplasms derived therefrom. The choroid plexus was involved in the pathological process of leukemic cell infiltration in one case reported here and in chronic cryptococcal leptomeningitis in the other case. The epithelial cells of the choroid plexus of the lateral ventricle were arranged extensively in a tubular (acinar) configuration, in association with remarkable stromal fibrosis caused by an infiltration of leukemic or inflammatory cells. In addition, choroid plexus epithelial cells in the first case contained a moderate amount of intracytoplasmic glycogen. These two cases indicate that the non-neoplastic choroid plexus epithelium can undergo transformation into a tubular (acinar) structure as a response or adaptation to the fibrotic processes of the stroma. This finding should be differentiated from metastatic adenocarcinoma. This finding also provides some suggestions as to the pathogenesis of "tubular (acinar) adenoma," a rare variant of benign choroid plexus neoplasm.