Magnetic resonance imaging of estrogen-induced pituitary hypertrophy in rats.

Estrogen-induced pituitary hypertrophy has been studied using magnetic resonance imaging in a group of 15 control and 30 experimental rats. Following the subcutaneous implantation of an estrogen pellet, differences in the anatomical appearance of the pituitary gland of the implanted rats can be detected in as little as 16 days, when compared to the control animals. The gland in the experimental animals appears diffusely enlarged with rounded margins, when viewed in sagittal T1-weighted magnetic resonance images. Additionally, a uniform signal intensity is not detected in the hypertrophic pituitary glands of estrogen-implanted rats, while in the control rats this is a common finding. A satellite study of 300 animals (treated in a manner identical to that in the imaging study) demonstrates that the weights of excised pituitaries in estrogen-treated rats increases to a statistically significant level in the interval 18 to 35 days. Changes in the appearance and volume of the pituitary gland observed with magnetic resonance imaging seem to have promise for the early detection of pituitary lesions in rats.