Pituitary Adenomas Classification

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Pituitary adenomas have been classified historically as acidophilic, basophilic and chromophobic. Adenomas may show a variable staining pattern with conventional hematoxylin and eosin dyes, so it is difficult to classify adenomas based on these stains.

Immunohistochemistry, ultrastructural studies and in situ hybridization analyses for specific hormones are the most reliable methods of classifying pituitary adenomas today. Immunohistochemical staining of pituitary adenomas with specific antibodies has reliably classified adenomas using highly purified polyclonal and monoclonal antibodies against prolactin, GH, ACTH, FSH-b LH-b, and TSH-b.

Many studies with these antibodies have revealed that some pituitary tumors are composed of several cell types, which produce various hormones. Some adenomas may not store specific hormones, so immunohistochemical staining may be weak or absent. The mRNA is usually present in the cytoplasm of adenomas.

Localization of mRNA for specific protein hormones is becoming more widely used in the classification of pituitary adenomas. Null-cell adenomas constitute up to 25% of pituitary neoplasms.

Selective venous sampling from the inferior petrosal sinus via transfemoral catherization is an effective method to compare venous effluent from the pituitary to systemic levels for a specific hormone. In addition, this technique may demonstrate laterality. This latter issue is potentially important as certain small adenomas may not be discernible from the gross appearance at surgery.

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