Patients who are suspected of having a pituitary tumor resulting in Cushing’s disease may require this procedure. Inferior petrosal sinus sampling is an important diagnostic test to differentiate Cushing’s disease (pituitary tumor) from Cushing’s syndrome. Occasionally an individual may have extremely high cortisol levels; however, an MRI of the pituitary does not visualize a tumor.
The inferior petrosal sinus sampling procedure is performed in the radiology department. This is an outpatient procedure where the patient is awake throughout the test. Patients are typically given a mild sedative and a local anesthetic. Catheters are inserted through the femoral veins and threaded to the petrosal sinuses. These sinuses lie along the internal aspect of the skull base and drain blood from the pituitary gland. Serum ACTH samples are drawn from the left and right pertrosal sinuses and peripheral vein. Thereafter, corticotrophin-releasing hormone is administered through the peripheral vein. Repeat serum ACTH samples from all three locations are obtained at 2, 5 and 10 minutes after the administration of CRH. Additonal X-rays are taken to confirm the catheters are not dislodged from their site during the sampling procedure. After the catheters are removed, patients are observed for 4 hours following the procedure ensuring that no bleeding from the femoral vein puncture sites occur.
A blood thinner might be used depending on the patient’s anatomy, medical history and potential to develop a blood clot. Interior pertrosal sampling procedure is minimally invasive and involves minimal discomfort. A sterile technique is used to minimize the risk of infection and the dose of radiation used is small. An allergic reaction may occur in response to the dye, bruising at the insertion catheter site and the development of a blood clot after completion of the procedure. Physicians and nurses will be available during and after this procedure which decreases the likelihood of serious complications.
To interpret the results, the ACTH from the left petrosal and right petrosal samples are compared to the peripheral samples. The ratios help to determine whether or not a patient’s Cushing’s syndrome is pituitary or from a non-pituitary source.