Cytology of pituitary thyrotroph hyperplasia in protracted primary hypothyroidism

Pituitary thyrotroph hyperplasia, a rare cause of pituitary enlargement, is usually associated with protracted primary hypothyroidism. We present here a case of pituitary thyrotroph hyperplasia in a 51 year old woman who was thought to have a pituitary macroadenoma with suprasellar extension. The cytologic investigation of the intraoperative touch preparation identified hyperplastic thyrotrophs, provided the correct diagnosis and helped to limit further aggressive surgical removal of the lesion, which is known to regress after adequate thyroid hormone replacement therapy. This is the first study to describe the cytologic features of pituitary thyrotroph hyperplasia confirmed subsequently by histology, immunocytochemistry and transmission electron microscopy.