[Transient thickening of the pituitary stalk followed by a supra-pituitary Langerhansian histiocytosis : consequence or mere coincidence ?].

One of the difficult challenges in endocrinology is the etiological diagnosis of isolated thickened pituitary stalk (PS). We report the case of a woman in whom a thickened PS was diagnosed following the onset of central diabetes insipidus revealed by polyuria-polydypsia syndrome of late pregnancy and postpartum. The pituitary exploration showed panhypopituitarism with disconnecting hyperprolactinemia. An etiological investigation for an inflammatory, granulomatous or tumour cause was carried out, but was negative. Postpartum lymphocytic hypophysitis was then retained. However, the course was puzzling with a control pituitary MRI showing disappearance of the PS thickening with paradoxical appearance of a supra-pituitary tumour, the biopsy of which concluded of being a Langerhansian histiocytosis. This paradoxical sequence is unusual and has not been reported before. It called into question the autoimmune lymphocytic origin of the thickened PS, initially considered, and raised the likelihood of a causal relationship between this PS thickening and Langerhansian histiocytosis.