Diagnostic and Operative Utility of Bilateral Inferior Petrosal Sinus Sampling in ACTH-Dependent Cushing Syndrome...

Accurate localization of adrenocorticotropic hormone (ACTH) secretion is crucial for the surgical management of ACTH-dependent Cushing's syndrome. While magnetic resonance imaging (MRI) and biochemical testing aid diagnosis, bilateral inferior petrosal sinus sampling (BIPSS) remains a reference standard in diagnostically challenging cases. In the absence of corticotropin-releasing hormone (CRH), vasopressin may serve as an effective alternative corticotroph stimulant during BIPSS; however, its additional benefit in lateralizing corticotroph adenomas remains uncertain.

To evaluate the diagnostic utility of BIPSS using vasopressin in selected patients with ACTH-dependent Cushing's syndrome and compare its accuracy with the high-dose dexamethasone suppression test (HDDST) and MRI in localization and lateralization.

Fourteen patients with biochemically confirmed ACTH-dependent Cushing's syndrome underwent HDDST, pituitary MRI, and BIPSS with Vasopressin as a corticotroph stimulant. BIPSS was performed to confirm a central source of ACTH secretion and assess lateralization. Transsphenoidal surgery (TSS) was performed in selected patients based primarily on MRI findings.

Of 14 patients, 13 were diagnosed with Cushing's disease (CD) and one with ectopic ACTH secretion. BIPSS correctly identified a pituitary source in all Cushing's disease cases, while HDDST yielded false negatives in three cases (sensitivity 76.9%). Concordance lateralization between BIPSS and MRI was observed in eight of 13 CD cases (61.5%). Among nine patients who underwent TSS, five achieved remissions; four of these had concordant BIPSS and MRI lateralization.

BIPSS is a valuable adjunct and remains a diagnostic tool for confirming pituitary origin in ACTH-dependent Cushing's syndrome, particularly when MRI and HDDST findings are inconclusive. Although vasopressin-stimulated BIPSS did not improve lateralization in this cohort, a higher proportion of patients achieving remission demonstrated concordant MRI and BIPSS findings; however, this observation should be interpreted cautiously due to the small sample size. BIPSS should not be used routinely but should be reserved for carefully selected cases with persistent diagnostic uncertainty.