Progressive pituitary hyperplasia over the course of 2 years demonstrated on magnetic resonance imaging in a patient with long standing, profound primary hypothyroidism

Pituitary hyperplasia secondary to primary hypothyroidism and subsequent regression following thyroid replacement has been well described. We report a 12 year-old male who was retrospectively found to have progressive pituitary hyperplasia over the course of 2 years prior to his diagnosis of primary hypothyroidism, as documented on annual brain magnetic resonance imaging (MRI) for Arnold Chiari Type 1 malformation. He presented to Endocrinology with a 2-year history of fatigue, worsening daily headaches and linear growth deceleration. The diagnosis of primary hypothyroidism as the cause for his pituitary hyperplasia was made. He was started on levothyroxine with subsequent regression of pituitary hyperplasia demonstrated on repeat brain MRI six months later. This case is the first that demonstrates progressive pituitary hyperplasia from early in the course to diagnosis of hypothyroidism. It also illustrates that pituitary hyperplasia noted on routine brain MRI can be a presenting sign of primary hypothyroidism that should prompt endocrinologic evaluation.