Inferior Petrosal Sinus Sampling
For what condition is inferior petrosal sinus sampling performed?
The pituitary gland sits along the skull base at the base of the brain and regulates a wide variety of hormone-mediated processes throughout the body. A pituitary adenoma is a benign type of tumor that may be microscopic or quite large and obvious on a brain MRI. Furthermore, adenomas may be functional, in that they secret abnormally high levels of hormones affecting normal body physiology, or are nonfunctional (20-30%) and only symptomatic if they grow large enough to affect surrounding structures. Tumors may therefore be symptomatic from abnormal hormone levels even at a small size. There are a variety of types of cells with special functions in the pituitary gland. The cell type of interest is known as a corticotroph and adenomas of this cell type represent approximately 10% of all adenomas. The most classic constellation of symptoms for functional adenomas of this type is called Cushing syndrome and is related to chronically elevated cortisol levels. This may lead to weight gain, deposition of fat (characteristically in the face, midsection, and upper back), purple stretch marks, easy bruising, fatigue, and weakness. The syndrome can be due to sources other than a pituitary adenoma, including steroid medications or other types of tumors throughout the body. If a pituitary tumor is the confirmed source of symptoms, this is then known as Cushing disease. If a pituitary source is suspected, sampling the veins associated with the pituitary gland and analyzing the hormone levels can help confirm and localize a pituitary adenoma for a surgeon to treat. This effectively rules out etiologies as the source of abnormal hormone secretion.
How is inferior petrosal sinus sampling performed?
Inferior petrosal sinus sampling (IPSS) is performed under conscious sedation under x-ray guidance. We access the femoral vein in each leg and advance a catheter through both access points to the inferior petrosal sinuses (IPS). The IPS is a primary draining vein for the pituitary system on either side of the skull base. A pituitary stimulant medication is administered intravenously (Corticotropin-Releasing Hormone (CRH)) and samples of venous blood are collected from the IPS and several additional locations at predetermined time points. All of these blood samples are then sent to the laboratory for detailed analysis and mapping out of the hormone levels. Collectively, this information allows us to determine if abnormal hormone levels are present and what the distribution is. By analyzing both, we are able to confirm the presence of a functional pituitary adenoma and the presumed side of the pituitary gland it is affecting.