Pituitary adenomas must be clearly differentiated from other
tumors of the sellar region (especially
meningiomas,
granular cell tumors,
chordomas and
germinomas), which may look very similar. The sub-classification of
adenomas depends on the methods used, in particular the immunostaining for
pituitary hormones. This sub-classification is not necessary in every case, but must be performed if unusual findings are observed during surgery or if surgery is unsuccessful and radiation or
drug-therapy is planned. Special structures and non-immunohistochemical stainings are very helpful for typing
adenomas. We differentiated monohormonal densely or sparsely granulated GH-cell
adenomas, monohormonal sparsely or very rarely densely granulated
prolactin cell
adenomas, monohormonal densely or sparsely
ACTH-cell
adenomas, monohormonal TSH-cell
adenomas and FSH/LH cell
adenomas from bihormonal
adenomas of mammosomatotroph or GH/
prolactin cell type or of the acidophil stem cell
adenoma type. The number of plurihormonal
adenomas decreased with the use of improved
monoclonal antibodies. Clinically inactive
adenomas are classified as null cell
adenomas, oncocytic
adenomas or FSH/LH-cell
adenomas. These appear as subtypes of one entity deriving from the gonadotroph cell type.
Craniopharyngiomas are classified into adamantinous and papillary types, which are not only structurally but also clinically different. If
adamantinous craniopharyngiomas show very strongly regressive changes, immunostaining for
keratin may be necessary to identify the squamous epithelia for the demonstration of
craniopharyngioma.