Thickened Pituitary Stalk on MR Images in Patients with Diabetes Insipidus and Langerhans Cell Histiocytosis

The MR images of four female patients with acute onset of central diabetes insipidus and pathologically confirmed Langerhans cell histiocytosis were evaluated retrospectively for evidence of lesions in the hypothalamic-pituitary axis. The examinations were conducted on a 1.5-T MR system with thin-section sagittal and coronal T1-weighted (short TR/short TE) and T2-weighted (long TR/long TE) images. Three patients underwent T1-weighted MR after IV administration of gadopentetate dimeglumine. Compared with 20 normal subjects who were evaluated with the same MR protocol, three of the four patients had a symmetrically thickened pituitary stalk that demonstrated homogeneous signal enhancement following contrast administration. The high signal intensity of the posterior lobe, which was seen in normal subjects on T1-weighted sagittal images, was absent in all four patients. Two patients had associated abnormalities on either chest films or imaging studies of the temporal bone and two patients had isolated CNS Langerhans cell histiocytosis. The combination of a thickened pituitary stalk and absent posterior pituitary hyperintensity, while nonspecific for Langerhans cell histiocytosis, should nevertheless prompt further studies, such as chest films, bone scanning, or temporal bone CT, to attempt to narrow the differential diagnosis. Gadopentetate dimeglumine, in particular, may be a useful adjunct in the MR examination of the patient with diabetes insipidus.