Aims: Early diagnosis and early treatment by transsphenoidal surgery is desirable for ACTH-producing pituitary microadenoma, but accurate localization of the functional lesion is not always possible before surgery because magnetic resonance (MR) imaging may provide false negative and/or positive findings. The diagnostic value of super-selective bilateral cavernous sinus sampling with the administration of corticotropin-releasing hormone (CRH) was assessed in patients with functioning ACTH-producing pituitary adenoma. Methods: Fifteen patients with pituitary adenoma (14 with microadenoma) aged from 23 to 74 years (mean 46.7 years) underwent cavernous sinus sampling with or without the CRH loading test and subsequent transsphenoidal surgery in our institute from October 1997 through to November 2002. MR imaging including dynamic scan failed to detect the adenomatous lesion in all patients. To eliminate the bias due to uneven blood flow in the cavernous sinuses and the multi-hormonal response to CRH administration, the ACTH/FSH ratios were evaluated. The inter-cavernous gradient (ICG) was calculated as the higher/lower ACTH venous blood levels in the right and left cavernous sinuses with or without CRH loading. The adjusted ICG was calculated using the ACTH/FSH ratios. The results were compared with the surgical findings. An ICG of 1.4 or greater was considered to indicate the localization of the responsible lesion. Results: Transsphenoidal surgery revealed the functioning lesion on the right in five cases, the left in six, the midline in three and the bilateral lateral wings (double adenoma) in one. Adjusted ICG with CRH loading had a localization accuracy of 93.3% (14/15), which was significantly higher than that of 73.3% (11/15) using ICG without hypothalamic stimulating hormone loading (p=0.0402). Conclusions: Super-selective cavernous sinus sampling with hypothalamic stimulating hormone administration can provide accurate localization of the responsible lesion in patients with ACTH-producing pituitary adenoma.
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