Bilateral and simultaneous venous sampling of inferior petrosal sinuses for ACTH and PRL determination: preoperative localization of ACTH-secreting microadenomas

We report our experience on venous sampling of the inferior petrosal sinuses for basal and CRH-stimulated ACTH and PRL gradients in 8 patients with surgically proven Cushing's disease who had normal preoperative neuroradiological studies. In 7 patients basal plasma ACTH concentrations in the inferior petrosal sinus ipsilateral to the tumor were higher than in the contralateral sinus; the gradients were enhanced by oCRH administration. In one out of two patients who had previously undergone unsuccessful pituitary microsurgery, neither basal nor oCRH-induced ACTH increases led to correct localization of the microadenoma within the pituitary. In 4 out of 7 patients basal serum PRL concentrations in the inferior petrosal sinus ipsilateral to the tumor were higher than in the contralateral; only two out of 4 showed an increase in PRL levels after oCRH injection. Our study confirms that simultaneous and bilateral venous sampling of inferior petrosal sinuses is a valuable means to identify the site of microadenomas in patients with Cushing's disease without neuroradiological evidence of the tumor. This procedure may give misleading results in patients previously operated on. Unilateral or predominant increases of PRL concentration during catheterization of the inferior petrosal sinuses, when present, always lateralize to the side of the corticotroph adenoma, providing a possible additional signal of the presence of the tumor.