COMPARATIVE-EVALUATION OF CONVENTIONAL AND DYNAMIC MAGNETIC-RESONANCE-IMAGING OF THE PITUITARY-GLAND FOR THE DIAGNOSIS OF CUSHINGS-DISEASE

OBJECTIVES The ability of MRI to detect pituitary ACTH-secreting adeno mas in patients with Gushing's disease is limited. Owing to different dynamics of contrast enhancement between adenomas and normal pituitary tissue, it has been suggested that obtaining images within seconds af ter gadolinium (Gad) injection using dynamic procedures increases the sensitivity of MRI in the detection of pituitary microadenomas. The ob jective of this study was to compare the ability of conventional magne tic resonance imaging (CMRI) and dynamic MRI (DMRI) to detect ACTH-sec reting pituitary adenomas. DESIGN Twenty-six consecutive patients with ACTH-dependent Gushing's syndrome and 10 normal subjects were investi gated. According to the results of inferior petrosal sinus sampling, 2 1 patients had Gushing's disease and five had ectopic ACTH syndrome. P atients with Gushing's disease were operated regardless of the results of imaging studies. All underwent identical MRI and DMRI procedures u sing a 1.0 T magnet. Image sampling time during DMRI was 19sec. Scans were randomly mixed and analysed blind, retrospectively and independen tly by two experienced radiologists. The clarity of the images was ass essed by the analysis of agreement among radiologists. MRI findings we re compared to surgical and histopathological findings. RESULTS Surgic al exploration identified three macrodenomas and 14 microadenomas, One microadenoma was found at pathological examination after subtotal hyp ophysectomy and no tumour was found in three cases. According to the c ombined opinion of radiologists, the three macroadenomas were identifi ed equally well with CMRI and DMRI. Eight ACTH-secreting microadenomas were detected with CMRI and 11 with DMRI, The three microadenomas det ected with DMRI only were visualized within 60 sec following Gad injec tion. No false positives occurred with CMRI. Three false positives wer e obtained with DMRI: one in a patient with ectopic ACTH syndrome whil e a silent microprolactinoma and normal tissue were found at the site of the radiological abnormality in two patients with Gushing's disease . In our study, the sensitivity of DMRI is greater than that of CMRI ( 0.67 vs. 0.52) but is associated with a loss in specificity (0.80 vs. 1.00). False positives may result from the increased sensitivity of DM RI which detects incidental pituitary lesions, technical artefacts or lowest clarity of images, as suggested by a lower observer agreement o f DMRI (Kappa statistic 0.66 vs. 0.83). Overall, the two MR procedures had equivalent diagnostic power (0.72). CONCLUSIONS In our hands, dyn amic procedures did not improve the usefulness of MRI in Gushing's syn drome.