Inferior Petrosal Sinus Sampling

Patients who are suspected of having a pituitary tumor resulting in Cushing's syndrome may be referred for inferior petrosal sinus sampling if findings on MRI examination of the pituitary did not reveal a tumor or are inconclusive.

The inferior petrosal sinus sampling procedure is performed in the radiology department. With the patient on the angiography table both groin regions are partially shaved, sterilized, and a local anesthetic is injected into the skin to provide pain relief. A tiny incision is made within the skin and a needle is inserted to puncture the femoral vein which drains blood from the leg. A small catheter is then inserted into the vein and flushed with an intravenous solution. Longer catheters are passed into the shorter catheters and advanced through the large veins traversing the torso into the neck and then into the base of the skull. Thereafter, a microcatheter is advanced through each of these larger guiding catheters and threaded into the inferior petrosal sinuses which lie along the internal aspect of the skull base and drain blood from the pituitary gland. Once these microcatheters have been positioned, contrast dye is injected and X-rays are taken to verify their position in the inferior petrosal sinuses. 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 2, 5, and 10 minutes after the injection. Additional X-rays are taken to confirm that the catheters were not dislodged from their site during the sampling procedure. Thereafter, the catheters are removed and direct pressure is applied to the groin region to decrease the likelihood of bruising. Patients are observed for 4 hours following the procedure to ensure that no bleeding from the femoral vein puncture sites will occur. Normal non-strenuous activity may be resumed 48 hours after the procedure.

Sedatives and pain relievers may be administered during the procedure as necessary. A blood thinner might be used depending on the patient's anatomy and the clinical suspicion of developing a blood clot. If a blood thinner is used, this may be counteracted with medication at the conclusion of the procedure to ensure that normal blood clotting resumes while removing the catheters. Overall, the inferior petrosal sinus sampling procedure involves minimal discomfort. The risks of the procedure are small. X-rays are used but the radiation doses are minimized. Infection is controlled by using sterile technique. Some patients might have an unexpected allergic reaction to the dye used during the study. A bruise may develop within the groin. Although rare, blood clots have developed in the groin veins following this procedure. Again, steps are taken to minimize the likelihood of each and every one of these complications.

ACTH levels 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.