Prolactinoma localization by inferior petrosal sinus sampling: illustrative case.

backgroundInferior petrosal sinus sampling (IPSS) is an established diagnostic technique used to distinguish between ectopic adrenocorticotropic hormone (ACTH) production and Cushing disease. The utility of IPSS outside of the differential diagnosis of ACTH-dependent hypercortisolism, however, is rarely reported. In this study, the authors describe the use of IPSS to lateralize a prolactin (PRL)-secreting adenoma in a patient with hyperprolactinemia and two distinct pituitary lesions. OBSERVATIONS: A 37-year-old female presented with symptomatic hyperprolactinemia that was refractory to escalating dopaminergic therapy. Sellar MRI demonstrated an 8-mm right-sided pituitary lesion and a distinct 5-mm left-sided pituitary lesion. IPSS was performed with PRL and ACTH measurements. Lateralization was assessed using both absolute PRL levels and PRL levels normalized to ACTH, and these data indicated right-sided PRL hypersecretion. The patient underwent successful endonasal endoscopic resection of the right-sided lesion, which was immunohistochemically positive for PRL, without removal of the left-sided lesion. She remained in remission 2.5 years after surgery, without evidence of hypopituitarism. LESSONS: This case highlights the potential utility of IPSS in selected patients with hyperprolactinemia and bilateral pituitary tumors. This technique may be helpful in guiding surgical decision-making in prolactinoma patients with multiple sellar masses. https://thejns.org/doi/10.3171/CASE25511.