Pituitary Hyperplasia and Primary Hypothyroidism

Abstract

Pituitary enlargement in primary hypothyroidism in adults and children is rare, and can result from both acquired and congenital hypothyroidism. Children present with growth arrest, mental retardation, and slightly increased body weight; some with precocious or delayed puberty; and very few with visual field defects. Visual deficits are more frequently described in adults together with the classical symptoms of hypothyroidism; in females, the combination of amenorrhea, galactorrhea, and hyperprolactinemia can erroneously suggest a prolactin-secreting pituitary adenoma. Pituitary hyperplasia secondary to primary hypothyroidism must also be distinguished from TSH-secreting adenomas where T4 levels are increased. On imaging studies, secondary pituitary hyperplasia is characterized by a spherical or calabash-like enlargement of the gland with suprasellar extension; its height can reach 18 mm and the optic chiasm can be distorted. The T1W signal is unchanged and the T2W signal can be slightly hyperintense; enhancement is homogeneous after gadolinium injection (Fig. 45.1). Cavernous sinus invasion is never noted. Shrinkage of the mass occurs very quickly, as soon as some weeks, after thyroxine hormone replacement therapy (Fig. 45.2)