Cushing's disease (CD) is a rare disease caused by ACTH secreting pituitary tumors, which cause the overproduction of glucocorticoid by the adrenal cortex. Because the overall mortality of patients with uncontrolled hypercortisolism is 4-5 times greater than that in the general population, appropriate treatment of CD is important. Surgical removal of the pituitary adenomas is the treatment of choice in patients with CD; however, until now there have been limitations for diagnosis and

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... n of the tumor because about 40-50% of corticotroph adenomas are too small to be detected even though by dynamic MR imaging. It has been reported, improved preoperative localization increases the cure rate of transsphenoidal surgery (TSS). Two principal preoperative examinations, inferior petrosal sinus sampling (IPSS) and dynamic MRI imaging are used to identify the tumor. None of the tests used in the diagnosis of CD is 100% reliable, and the best method for localizing pituitary microadenomas remains a challenge. Therefore, particularly in patients with discordant results between IPSS and MRI, the outcome of patients is primarily influenced by the neurosurgeon's ability. In this session, we will discuss 1. Diagnosis and differential diagnosis of CD; 2. Sensitivity and specificity of each imaging modality; 3. Usefulness of high-resolution MRI and IPSS for localizing pituitary adenomas; 4. A concept, surgical identification of tumors by a neurosurgeon and histological identification (SHI) during operation; 5. ACTH secreting pituitary carcinoma; and 6. Reactivation of silent corticotrope adenoma.