PITUITARY-TUMOR LOCALIZATION IN PATIENTS WITH CUSHINGS-DISEASE BY MAGNETIC-RESONANCE-IMAGING - IS THERE A PLACE FOR PETROSAL SINUS SAMPLING

OBJECTIVE We wished to analyse the relative value and diagnostic accur acy of bilateral simultaneous inferior petrosal sinus blood sampling f or plasma ACTH measurements when compared with pituitary magnetic reso nance imaging (MRI) for the preoperative localization of microadenoma (tumour diameter <10 mm) within the pituitary fossa in patients with C ushing's disease. DESIGN Pituitary MRIs were assessed blind and indepe ndently. The sinus blood sampling was performed before and after admin istration of corticotrophin releasing hormone (CRH). The ratios of the ACTH concentrations in plasma samples from the inferior petrosal sinu ses to the concentrations in peripheral blood plasma samples (the IPS: P ratio) and the ratios of the ACTH concentrations in samples from bot h inferior petrosal sinuses (the intersinus gradient) were calculated. PATIENTS Twenty consecutive patients with Cushing's disease were pros pectively studied. All but two patients subsequently underwent transsp henoidal exploration of the pituitary fossa. RESULTS In three of 20 pa tients (15%), positioning of catheter tips in both inferior petrosal s inuses was unsuccessful. The diagnosis of Cushing's disease was confir med by the greater basal IPS:P ratio amounting to greater than or equa l to 2.0 in 13 of 17 patients (76%), and amounting to greater than or equal to 3.0 in CRH-stimulated peak samples in 15 of 17 patients (88%) . Anatomical variations of the inferior petrosal sinus, precluding rel iable conclusions about lateralization of pituitary venous ACTH draina ge, were observed in five of 20 patients (25%). Adding the three patie nts with technical failure and one patient who presented with a macroa denoma (tumour diameter 11 mm), this left interpretable data with rega rd to lateralization of the microadenomas in only 11 of 20 patients (5 5%). In 15 of 20 patients (75%) a pituitary microadenoma was found at MRI. In 14 of these 15 patients (93%) a tumour was indeed found at tha t position at subsequent transsphenoidal operation. Concordance betwee n the lateralization by the intersinus gradient and microadenoma local ization by MRI was observed in six of 11 cases (55%) when using basal samples and in seven of 11 cases (64%) when using peak samples obtaine d after stimulation with CRH. Concordance between the lateralization b y the intersinus gradient and subsequent microadenoma localization at surgery was observed in seven of 11 patients (64%) before and in eight of 11 cases (73%) after CRH stimulation. Reversal of the intersinus g radient after CRH stimulation, suggesting a shift in the lateralizatio n to the contralateral side of the gland, was found in three of 12 cas es (25%). CONCLUSIONS Bilateral simultaneous inferior petrosal sinus b lood sampling for plasma ACTH measurements before and after CRH stimul ation successfully confirmed the diagnosis of pituitary dependent Cush ing's disease in 15 of 17 patients (88%) in whom this diagnosis was su spected on the basis of conventional biochemical testing. Magnetic res onance imaging, however, is superior to bilateral simultaneous inferio r petrosal sinus brood sampling for the localization/lateralization of pituitary microadenomas in patients with Cushing's disease. Therefore , bilateral simultaneous inferior petrosal sinus blood sampling should be reserved for the assessment of those patients with Cushing's syndr ome in whom either the results of biochemical tests are equivocal and/ or subsequent pituitary magnetic resonance imaging gives unconvincing results.