Knosp Classification (Pituitary Adenoma)

The Knosp classification (1993), revised by Micko and colleagues (2015), stratifies cavernous sinus involvement by pituitary adenomas. On coronal post-contrast T1-weighted images, three reference lines are drawn through the intracavernous and supracavernous internal carotid artery segments: the medial tangent, the intercarotid line connecting the vessel centers, and the lateral tangent. Tumor medial to the medial tangent is grade 0; progression across each line raises the grade to 1, 2, or 3; complete encasement of the intracavernous ICA is grade 4. The revision splits grade 3 into 3A (extension above the ICA into the superior cavernous sinus compartment) and 3B (below the ICA into the inferior compartment), a distinction with major prognostic weight: endoscopic series found true invasion in roughly a quarter of 3A tumors but about two-thirds or more of 3B tumors, with corresponding differences in resectability and endocrine remission.