IMAGING OF THE SELLA IN THE SYNDROME OF INAPPROPRIATE SECRETION OF ANTIDIURETIC-HORMONE

Objective. The syndrome of inappropriate secretion of antidiuretic hor mone (SIADH) results either from ectopic production or inappropriate r elease of antidiuretic hormone from the neurohypophysis. Although magn etic resonance imaging (MRI) has provided new insights into the morpho logical changes of the hypophysis in health and disease, no previous s tudies have evaluated its use in SIADH. The aim of this study was to e valuate the MRI appearance of the neurohypophysis in patients with SIA DH. Design. Retrospective case-control study. Setting. Tertiary care t eaching hospital. Subjects. We studied retrospectively eight patients with SIADH who had been hospitalized in Boston's Beth Israel between 1 984 and 1994 and who had MRI scans including the sella turcica, We als o evaluated prospectively the MRIs of the heads of 23 consecutive cont rol patients who had no pituitary pathology and no serum osmolality or electrolyte abnormalities. Interventions. Clinical evaluation as well as sagittal and axial T1-MR images.Main outcome measures. Presence or absence of the high intensity signal of the neurohypophysis. Results. In seven out of eight patients (87.5%) the normal high intensity sign al of the neurohypophysis was not present, In one patient (12.5%), two interpreting radiologists disagreed about its presence. The high inte nsity signal was present in the neurohypophysis of 20 out of 23 contro ls (87.5%). Conclusions. Our data indicate an association of SIADH wit h the absence of the normal hyperintense signal of the neurohypophysis , confirming the usefulness of MRI as a tool to visualize ADH processi ng. These data also raise the possibility that the absence of the high intensity signal may be a useful diagnostic tool in cases of SIADH th at are difficult to diagnose clinically. Additional studies to correla te this signal with various forms of SIADH will be needed.