RÉSUMÉ
Lymphocytic infundibuloneurohypophysitis was known as a cause of idiopathic central diabetes insipidus. Until recent time, it is characterized into two groups. One has thickening of the pitutitary stalk, enlargement of the neurohypophysis and loss of hyperintense signal of the normal neurohypophysis, the other has only loss of hyperintense signal but not morphological change. A 51-year-old man presented with a one month history of polydipsia and polyuria. The interpretation of water deprivation test was compatible with complete central diabetes insipidus. Endocrinologic examination of the adenohypophysis hormones and its triple stimulation test were normal apart from thyroid stimulating hormone (TSH), which showed low response despite thyrotropin releasing hormone (TRH). Sellar MRI scan disclosed an loss of hyperintense singnal of normal neurohypophysis and about 10 mm-sized nodular mass lesion on neurohypophysis. However, thickness of the pituitary stalk was normal. Pathologic examination demonstrated diffuse infiltration of lymphocytes and plasma cells. No adenomas, menigitis, sarcoidosis or granulomas were present. We supposed that this case was an atypical type of lymphocytic infundibuloneurohypophysitis, which did not belong to any other part of two groups described above.