Inferior petrosal sinus sampling

Inferior petrosal sinus sampling is the diagnostic gold standard for localizing the source of adrenocorticotropic hormone dependent Cushing syndrome when pituitary imaging is non diagnostic or discordant. The procedure relies on comparing simultaneous central venous hormone concentrations from each petrosal sinus against peripheral levels, both at baseline and following administration of a secretagogue such as desmopressin or corticotropin releasing hormone. A central to peripheral gradient confirms a pituitary corticotroph source, whereas a flat gradient points toward ectopic secretion. Concomitant measurement of prolactin validates successful catheterization of the pituitary venous effluent and assists in interpreting borderline or discordant adrenocorticotropic hormone ratios.