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

Objective. The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) results either from ectopic production or inappropriate release of antidiuretic hormone from the neurohypophysis. Although magnetic resonance imaging (MRI) has provided new insights into the morphological changes of the hypophysis in health and disease, no previous studies have evaluated its use in SIADH. The aim of this study was to evaluate the MRI appearance of the neurohypophysis in patients with SIADH. Design. Retrospective case-control study. Setting. Tertiary care teaching hospital. Subjects. We studied retrospectively eight patients with SIADH who had been hospitalized in Boston's Beth Israel between 1984 and 1994 and who had MRI scans including the sella turcica, We also evaluated prospectively the MRIs of the heads of 23 consecutive control 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 signal of the neurohypophysis was not present, In one patient (12.5%), two interpreting radiologists disagreed about its presence. The high intensity signal was present in the neurohypophysis of 20 out of 23 controls (87.5%). Conclusions. Our data indicate an association of SIADH with the absence of the normal hyperintense signal of the neurohypophysis, confirming the usefulness of MRI as a tool to visualize ADH processing. These data also raise the possibility that the absence of the high intensity signal may be a useful diagnostic tool in cases of SIADH that are difficult to diagnose clinically. Additional studies to correlate this signal with various forms of SIADH will be needed.