Patients who are suspected of having a pituitary tumor resulting in Cushing's syndrome may be referred for inferior petrosal sinus sampling. In this procedure, catheters are inserted into the femoral vein of each leg and guided into the inferior petrosal sinuses which lie along the internal aspect of the skull base and drain blood from the pituitary gland. Next, blood samples are collected from both catheters in the inferior petrosal sinuses and from a peripheral (usually arm) vein. Thereafter, corticotropin-releasing hormone is administered through the peripheral vein. Repeat blood samples are drawn after the injection.
Levels of the hormone ACTH are measured in each of the blood samples obtained during the procedure. The ratios between the petrosal sinus sampling and the peripheral vein samples are compared. The results are used to determine whether ACTH production is due to either a pituitary or a non-pituitary source.
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