Bilateral simultaneous inferior petrosal sinus sampling, associated with the oCRH stimulation test (100 µg i.v. as a bolus) was performed in 22 patients with Cushing’s syndrome and no signs of pituitary abnormalities. Catheters were inserted into both femoral veins. More than one site in the superior and inferior vena cava was sampled before reaching the inferior petrosal sinuses. Blood samples for ACTH and β-endorphin were gently aspirated from both petrosal sinuses and from a peripheral vein simultaneously. Blood was drawn at 0, 5, 10 and 15 min after oCRH injection. Seventeen of 22 patients showed an ipsilateral to peripheral vein ratio higher than 1.5, and 12 patients showed a lateralization of ACTH levels after oCRH stimulation. Seventeen patients underwent transsphenoidal pituitary surgery. Nine patients had a pituitary adenoma at the expected side; 1 at the contralateral side, while in 2 it was central. Three of 4 patients in whom the ipsilateral/peripheral ratio was less than 1.5 had the highest ACTH levels at the superior or inferior vena cava, not responsive to oCRH stimulation. One of these had a mediastinal and one a pulmonary mass. The third one, with an occult ectopic source, is still under investigation. At immunohistochemical and biological in vitro studies, both tumors were shown to secrete ACTH. In 13 patients in whom both β-endorphin and ACTH measurements were performed, these hormones showed similar patterns of response. In conclusion, simultaneous bilateral petrosal sinus catheterization is a useful tool in the differential diagnosis of Cushing’s syndrome as concerning pituitary and ectopic forms. The finding of a ratio <1.5, especially after oCRH stimulation, between pituitary/peripheral sites strongly suggests the existence of an ectopic ACTH-secreting tumor. In the pituitary forms, an oCRH stimulation test performed during the procedure may clearly indicate the site of ACTH hypersecretion.

The most common lesion in Cushing’s disease is an anterior pituitary adenoma. However, normal or hyperplastic corticotropic pituitary tissue has also been found in some cases. In an attempt to distinguish the patterns of ACTH response to oCRH in different forms of anterior pituitary hypersecretion, 17 patients with pituitary adenoma and 17 without pathological evidence of adenoma were studied. These patients underwent transsphenoidal pituitary surgery by the same surgeon and were retrospectively evaluated. The diagnosis of pituitary lesions was confirmed by microscopical and immunohistochemical studies. Patients without pituitary adenoma showed a higher and more prolonged mean plasma ACTH response than that observed in patients with pituitary tumors. In patients with pituitary adenoma, the peak ACTH response was observed within 30 min after oCRH administration, and was followed by a gradual decrease to basal levels in the following 30 min. In those cases in whom no pituitary adenoma was found, oCRH injection produced a marked increase in plasma ACTH levels during the first 60 min with a slower decline at the subsequent time points. The mean response curves of the two groups, analyzed by Beherens-Fischer nonparametric ANOVA, showed significant differences, either when they were compared globally (p < 0.01), or at single time points. Differences in ACTH response to oCRH stimulation support the hypothesis of different pathogenetic mechanisms leading to ACTH hypersecretion in Cushing’s disease with and without pituitary adenoma.