To propose a subclassification of KG4PA by analyzing the different characteristics between KG4PAs with a focus on the tumor growth pathway and its relationship to the cavernous segment of internal carotid artery.

A subclassification scheme was proposed based on the tumor growth pathway and its relevant features. Clinical data from 129 patients with KG4PAs who underwent endoscopic endonasal surgery were reviewed.

The KG4PAs were classified into 3 types based on the tumor growth pathway and its relevant features: groups A, B, and AB. The type A KG4PA invaded the CS through the breach of medial wall of cavernous sinus (MWCS) above the horizontal segment of ICA (hsICA); the type B KG4PA invaded the CS through the breach of MWCS below hsICA; and the type 4AB Kg4PA invaded the CS through the breaches both below and above hsICA. The gross total resection rate in group A (51.2%) was much lower than that in group B (87.5%) and AB (87%) with a significant difference between the 3 groups (P=.0004). 

The subclassification strengthens our understanding of KG4PAs on tumor

growth corridors and topographic relations of tumor and cavernous segment of internal

carotid artery.