Inferior petrosal sinus sampling (or IPSS), is a diagnostic medical procedure used to determine whether excess
adrenocorticotropic hormone (ACTH) is coming from the
pituitary gland (usually a
pituitary adenoma causing
Cushing's disease) or from a source outside the pituitary (a rare tumor causing
ectopic ACTH syndrome). The procedure is usually reserved for patients with consistent ACTH-dependent Cushing's syndrome without a clear cut lesion on pituitary MRI.[1]
Procedure
The procedure is typically performed in large medical centers by an experienced
interventional radiologist,
neurologist or
neurosurgeon and guided using
fluoroscopy. Catheters are inserted through the
jugular or
femoral veins into both inferior petrosal veins which drain blood from the pituitary gland. To maximize and stabilize the pulsatile ACTH secretion, a dose of intravenous
corticotropin-releasing hormone (CRH) is usually given. ACTH levels are measured in the petrosal (central) and peripheral venous plasma before and within 10-12 minutes after administration of CRH. Where CRH is unavailable some centers use
desmopressin.[2] Measurement of the central-to-peripheral
prolactin ratio can assist in verifying the correct placement of the catheters as well as in normalization of ACTH levels. In experienced centers, successful bilateral catheterization is reported in up to 90% of cases with very rare major complications.[3][4]
Interpretation
In patients with true
hypercortisolism, a central-to-peripheral ACTH gradient of ≥2 before, or ≥3 after CRH administration, is considered diagnostic for a pituitary source of ACTH.[5] Some studies have shown that if catheters were appropriately placed, a gradient of ≥1.4 for ACTH concentrations between the two sinuses predicted the side of the tumor with ~70% accuracy.[6]