MRI in diabetes insipidus due to metastatic breast carcinoma.

Magnetic resonance imaging (MRI) has been established as a valuable imaging modality in the evaluation of pituitary disorders. We describe three women with known carcinoma of the breast, who presented acutely with biochemically proven diabetes insipidus (DI), in whom MRI was used as the primary investigative tool. The patients were studied using a 1.5T superconducting system, with gadolinium enhancement in two cases. All three had thickened pituitary stalks and two had complete loss of the normal high signal from the posterior lobe of the pituitary gland. Two also had enlargement of the anterior pituitary gland. One subject was also noted to have other metastases to the brain. All three had multiple secondary deposits elsewhere in the body and one had metastases to the clivus but without evidence of extension to the pituitary fossa. DI is uncommon in systemic cancers and anterior pituitary dysfunction much more so, due to the separate blood supply of the two lobes. Thickening of the stalk has not been found frequently in large autopsy series. In the clinical context of DI in a patient with a known primary tumour the loss of high signal from the posterior lobe and stalk thickening are indicative of infiltration by metastases. A pituitary mass or metastases to adjacent bones are not necessary for diagnosis.