Panhypopituitarism in a patient with a hypothalamic and pineal germ cell tumor

SUMMARY: Central diabetes insipidus (DI) is characterized by decreased release of antidiuretic hormone, resulting in a variable degree of polyuria. The etiologies are variable, with the vast majority of cases either being idiopathic or resulting from primary or secondary tumors. Such tumors include craniopharyngioma, Langerhans cell histiocytosis, or a variety of inflammatory, vascular, or granulomatous diseases. It is exceptionally rare for pituitary adenomas to present with DI. We describe a young patient who first presented with symptoms consistent with DI. He was tested for DI and found to have panhypopituitarism due to a metastatic pineal germ cell tumor causing thickening of his pituitary stalk. LEARNING POINTS: New onset central diabetes insipidus requires dedicated pituitary MRI for determination of etiology. Germ cell tumors in the pineal and suprasellar regions most commonly cause central diabetes insipidus. Determining the etiology of new-onset central diabetes insipidus can radically affect treatment.