The inferior petrosal sinus runs along the inferior border of the petrous temporal bone in the petrous-occipital fissure, connecting the cavernous sinus anteriorly to the internal jugular vein at the jugular foramen posteriorly. It drains the cavernous sinus, the anterior brainstem, and the inferior cerebellum. The abducens nerve (CN VI) crosses between the two inferior petrosal sinuses at the clivus.
Bilateral inferior petrosal sinus sampling (BIPSS) is the gold standard diagnostic test for Cushing disease, performed by sampling ACTH from both inferior petrosal sinuses simultaneously before and after CRH stimulation. A central-to-peripheral ACTH gradient greater than 2:1 (or 3:1 after CRH) confirms pituitary ACTH secretion, and lateralisation of the gradient toward one sinus helps predict which side of the pituitary gland contains the adenoma. The technique is performed by interventional radiologists via femoral vein catheterisation.
Bilateral inferior petrosal sinus sampling with CRH stimulation differentiates pituitary Cushing disease from ectopic ACTH secretion with near 100% sensitivity, providing lateralisation information that guides the pituitary surgeon toward the side more likely to contain the microadenoma.
Rare thrombosis of the inferior petrosal sinus, extending from cavernous sinus thrombosis or occurring de novo, can compress the abducens nerve in the sinus canal producing lateral gaze palsy as part of the broader cavernous sinus syndrome.
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