MR demonstration of pituitary hyperplasia and regression after therapy for hypothyroidism.

In many centers , MR has become the imaging study of choice for evaluating diseases of the pituitary [1] . The diagnosis of pituitary adenoma is confirmed by showing a gland that is more than 1 0 mm in height with or without associated sellar deformity and deplacement of the pituitary stalk. We report a case of a hypothyroid patient with elevated levels of serum prolactin and a homogeneously enlarged pituitary gland mimicking a pituitary adenoma on T1-weighted (TR/ TE = 600/20) MR images. The pituitary enlargement and hyperprolactinemia resolved after thyroid hormone replacement. To our knowledge, this is the first case for which MR depiction of pituitary hyperplasia and subsequent regression after thyroid replacement therapy has been described.