Objective To evaluate magnetic resonance imaging（MRI）characteristics and surgical results of adrenocorticotropin（ACTH）-secreting pituitary adenomas.Methods MRI characteristics and relationship between MRI positive rate and surgical results of 266 patients with pathologically confirmed Cushing’s disease were analyzed retrospectively.All patients underwent thin-section sagittal and coronal scans of the pituitary gland before and after administration of gadolinium-diethylene triamine pentaacetic acid（Gd-DTPA）on a 1.5 Tesla MRI scanner

and dynamic enhanced MRI was performed in 39 patients.All patients underwent transsphenoidal adenomectomy.Endocrinological examinations and assessments were performed.Results Preoperative MRI revealed normal results in 41（15.4%）cases

microadenoma in 179（67.3%）

macroadenoma in 42（15.8%）

and huge adenoma in 4（1.5%）.Pituitary apoplexy was found in 13（4.9%）cases.Positive rate of ACTH-secreting adenomas was 84.6%（225/266）on MRI scans

and that of small microadenomas was 87.2%（34/39）on dynamic enhanced MRI scans.Preoperative endocrinological tests of 199 cases supported the diagnosis of typical Cushing’s disease

while the other 67 cases had atypical endocrinological results.The endocrinological cure rate

remission rate

and inefficacy rate were 85.7%

7.9%

and 6.4%

respectively.There was no difference in the initial endocrinological cure rate between the patients with positive and normal MRI results（90% vs.87.8%

P=0.904）.Conclusions Enhanced coronal pituitary MRI is helpful for preoperative localization of ACTH-secreting pituitary microadenoma.Dynamic enhanced MRI may improve detection rate of microadenoma.There is no marked difference in the surgical results for patients with preoperative MRI results indicating presence or absence of microadenoma.