Two cases of lymphocytic hypophysitis presenting with diabetes insipidus: A variant of lymphocytic infundibulo-neurohypophysitis

BACKGROUND It has been thought that neurohypophysial involvement manifesting as central diabetes insipidus in lymphocytic hypophysitis is uncommon. Although cases with such an association have been reported recently with increasing frequency, the relationship with lymphocytic infundibular neurohypophysitis remains unclear. METHODS AND RESULTS Two postmenopausal women who presented with diabetes insipidus are reported. Adenohypophysial function was normal in both cases, apart from growth hormone secretion. Magnetic resonance imaging revealed a sellar mass lesion mimicking pituitary adenoma, with loss of the hyperintense signal of the neurohypophysis in both cases and thickening of the stalk in one case. The lesion was located behind the residual adenohypophysis during transsphenoidal biopsy; however, histologic examination showed chronic inflammation of the adenohypophysis, findings identical to those of lymphocytic adenohypophysitis. Although the principal site of the inflammation was considered to be the neurohypophysial system, adenohypophysis was also involved in the lesion. We suggest that these cases represent a variant of lymphocytic infundibular neurohypophysitis. CONCLUSION To avoid unnecessary surgical intervention, it is important to note that some variants of lymphocytic infundibulo-neurohypophysitis may form a mass lesion not localized in the neurohypophysial system but involving the adenohypophysis, thus resembling adenomas and other tumors.