SMTs in patients with AIDS typically arise in multiple and very unusual sites that are not often observed in SMTs among immunocompetent individuals. Our series also suggests association between EBV infection and SMTs in patients with AIDS. The exact role of EBV in smooth-muscle oncogenesis awaits further study.

Four stages of development can be recognized in the histogenesis of the human telencephalic choroid plexus. Division into stages is based on alterations of outline of the plexus, characteristic appearance and biochemical content of the epithelial cells, and the components of the stroma. The stages are less distinctive in the myelencephalic and diencephalic plexus where differentiation is accomplished sooner than in the telencephalic plexus. Neuroepithelial-lined tubules are common in the choroid plexus, and are formed by folding of choroidal epithelium into the stroma. Some tubules are large enough to be designated as incipient neuroepithelial (colloid) cysts. Cysts having only connective tissue walls are also present. The choroidal epithelial cells proliferate focally, stratify and desquamate into intervillous clefts, or flow into the stroma by disruption of the epithelial basement membrane or tubular wall. These findings are confirmed by use of serial sections. The size of the developing telencephalic plexus relative to the ventricular system is small at first, then large, occupying almost the entire telencephalon, but gradually decreases during development. Glycogen is prominent i n developing choroidal epithelial cells, but disappears in the mature plexus. Both epithelial and mesenchymal mucin and mucopolysaccharides are identified in the plexus. The paraphysis is re-emphasized as an extraventricular choroid plexus on the basis of a common neuroepithelial origin. It is rudimentary and inconstant in man.We have reviewed in another publication the developmental and comparative anatomy of choroid plexus, ependyma and other derivatives of the primitive neuroepithelium in relation to the development of neuroepithelial (colloid) cysts (Shuangshoti, Roberts and Netsky, '65). It was emphasized in that paper that the paraphysis is an extra-ventricular choroid plexus. Because our data indicated a close relationship between the neuroepithelial cyst and the choroid plexus, we decided to study the histogenesis of the choroid plexus in detail. We described in the same paper the finding of mucin and PAS-reactive materials in neuroepithelial cysts and in fragments of choroid plexus attached to the cysts. Histochemical tests for these substances were therefore conducted on developing choroid plexus to clarify these observations. A few investigators have described the times of appearance of the primordia of telencephalic and myelencephalic plexuses in some mammals as in pig (Weed, '17), guinea pig, rabbit and rat (Cohen and Davies, '38; Strong, '56) but the full histogenesis has not been presented. Kiszely AM. J. ANAT., 118: 283-316.

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A case is reported of a combined neuroepithelial cyst and xanthogranuloma of the choroid plexus in the third ventricle of a 22-year-old woman. It is suggested that proliferated neuroepithelial cells lining the cyst enter the fibrous wall through the disrupted basal lamina, and then become xanthomatous cells. Disintegration of these foamy epithelial cells releases lipids and other materials into the cyst wall, provoking a response of macrophages and multinucleated giant cells of foreign-body type. A xanthogranuloma is then formed. The origin of "colloid" cysts is from neuroepithelium; these cysts arise from both ependyma and choroid plexus. Those cysts arising in or near the floor of the third ventricle may originate in stomodeal epithelium, but a distinction cannot be made from neuroepithelial cysts by presently available methods.

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