Intraventricular And Pineal Region Tumors

Fig. 13.4. Pineal region tumor presenting with progressive hydrocephalus from aqueductal obstruction. Pathology showed pineoblastoma.

depending on the degree of mixed cell types. Choriocarcinoma is often well demarcated and may contain regions of hemorrhage and necrosis. Teratomas are usually well defined, with an irregular or lobulated outer surface. These tumors may contain cartilage, bone and hair (rarely, teeth) [17]. Typically, the tumor has multiple cysts containing whitish fluid from the desquamation of the dermoid cell lining. Immature teratomas contain hemorrhage and central necrosis and have more invasive features.

Microscopically, germinoma is composed of two clearly distinguishable cell types: large germ cells and small lymphocytes [17]. The germ cells are large, polygonal or spheroidal cells with well defined cell boundaries and an eosinophilic, sometimes vacuolated, cytoplasm with large central spherical nuclei and pale nucleoplasm containing a central nucleolus. Mitotic figures and microscopic mineralization can be present. The second cell type consists of infiltrating lymphocytes clustered around tumor blood vessels. This is thought to represent a granulo-matous reaction, although the significance of the immunological reaction is unknown, particularly since this cellular reaction may be completely absent in some cases. The immuno-logical reaction has been found to be primarily a T-cell infiltrate. Occasionally, the local T-cell response predominates the histology, with the germinoma cells being few and difficult to identify. In these cases, confusion with primary cerebral lymphoma may occur. Occasionally, multinucleated syncytiotrophoblast giant cells can be seen, which stain for human chorionic gonadotropin (bHCG). Immunohistochemical stains are useful, since germinomas will stain positive for placental alkaline phosphatase and may show variable staining for cytoker-atins, the epithelial membrane antigen or vimentin [17].

Embryonal carcinoma is the least differentiated, having a monotonous pattern with aggregates of primitive epithelial cells in sheets and ribbons [17]. These tumors have the potential to differentiate toward embryonal structures, forming yolk sac or trophoblastic structures. Thus, embryonal carcinoma may give rise to mixed tumors and pure CNS embryonal carcinomas are exceedingly rare. Endodermal sinus tumor is histologically quite close to embryonal carcinomas. The key distinction is the predominance of retiform arrangements, papillary structures, PAS-positive alpha-fetoprotein (AFP)-containing hyaline globules and Schiller-Duvall bodies. Endodermal sinus tumor forms papillary projections constructed of low cuboidal epithelium.

Choriocarcinoma features two predominant cell types: cytotrophoblast and multinucleated syncytiotrophoblast. The cytotrophoblast is recognized by its epithelioid appearance, with clear cytoplasm and a single nucleus. The

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