TUMORS OF THE SELLAR REGION MIMICKING PITUITARY-ADENOMAS

In the sellar region most tumors of our collection (n = 1937) are pitu itary adenomas, followed by craniopharyngiomas, chordomas and meningio mas. Difficulties in morphological differential diagnosis by light mic roscopy may occur in meningiomas, plasmacytomas, chordomas and germino mas. In these cases, immunohistological investigations and sometimes e ven electron microscopy are helpful in solving the problems. Meningiom as can sometimes resemble pituitary adenomas. Of diagnostic value in t hese cases is the expression of vimentin and S-100-protein in the meni ngioma cells. Plasmacytomas may also mimic pituitary adenomas. In thes e cases, the positive reaction with antibodies against LCA and immunog lobulins or against kappa-light-chains and lambda-light-chains leads t o the diagnosis. Chordomas, too, can sometimes be hardly distinguished from pituitary adenomas. In these cases, the expression of S-100-prot ein, vimentin and CEA by the chordoma cells and the typical electron m icroscopic features of chordomas are helpful for the differential diag nosis. Germinomas may sometimes be indistinguishable from lymphocytic hypophysitis. Of diagnostic importance are here the expression of HCG and placental alkaline phosphatase by germinoma cells. In the above me ntioned cases, it is also important to perform immunohistochemical exa minations for pituitary hormones including alpha-subunit. All these tu mors do not express these hormones.