[A case of pituitary hyperplasia associated with primary hypothyroidism]

A thirteen-year-old girl was admitted complaining of short stature and anemia. The low titers of her serum T3 and T4 and the abnormally high TSH level represented primary hypothyroidism. Although she had normal sellar size, CT demonstrated an intra- and suprasellar round mass with homogeneous enhancement. With thyroid replacement therapy the enhanced mass diminished on CT within 5 months, and her symptoms regressed. Twelve cases with radiological diminution of pituitary mass or visual field improvement after thyroid replacement therapy are reviewed. They were considered to be pituitary hyperplasia, rather than pituitary adenoma, caused by long-standing untreated hypothyroidism. In four of them, the pituitary mass on CT was diminished after the therapy. Characteristic CT findings of pituitary hyperplasia, including our case, was a round isodensity mass with homogeneous enhancement in the midline of the pituitary region. In the experimental studies, pituitary hyperplasia is based on the feedback mechanism of hypothalamic-pituitary-thyroid axis, and ultimately autonomous pituitary adenoma may occur. Pituitary mass with hypothyroidism, visual field defect, amenorrhea or galactorrhea tend to be mistaken for prolactinoma or non-functioning adenoma with pituitary hypothyroidism. Thorough endocrinological examination must be carried out. The first choice of treatment for this type of pituitary mass should be thyroid replacement therapy. If there is no improvement of visual field, no regression of pituitary mass on CT, or continuing high TSH levels, then pituitary surgery must be considered.