In the sellar region most
tumors of our collection (n = 1937) are
pituitary adenomas, followed by
craniopharyngiomas,
chordomas and
meningiomas. Difficulties in morphological differential diagnosis by light microscopy may occur in
meningiomas,
plasmacytomas,
chordomas and
germinomas. In these cases, immunohistological investigations and sometimes even electron microscopy are helpful in solving the problems.
Meningiomas can sometimes resemble
pituitary adenomas. Of diagnostic value in these cases is the expression of
vimentin and S-100-protein in the
meningioma cells.
Plasmacytomas may also mimic
pituitary adenomas. In these cases, the positive reaction with
antibodies against LCA and
immunoglobulins or against kappa-light-chains and lambda-light-chains leads to the diagnosis.
Chordomas, too, can sometimes be hardly distinguished from
pituitary adenomas. In these cases, the expression of S-100-protein,
vimentin and CEA by the
chordoma cells and the typical electron microscopic features of
chordomas are helpful for the differential diagnosis.
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 mentioned cases, it is also important to perform immunohistochemical examinations for
pituitary hormones including alpha-subunit. All these
tumors do not express these
hormones.