Primary hypothyroidism mimicking a pituitary macroadenoma: regression after thyroid hormone replacement therapy

We report a 9-year-old girl with pituitary hyperplasia due to primary hypothyroidism. She presented with growth arrest, abnormal thyroid function studies, and a pituitary mass on MRI. With thyroxine therapy, the pituitary mass regressed and her symptoms resolved. Primary hypothyroidism should be considered in the differential diagnosis of solid mass lesions of the pituitary gland.