Combinatorial perisphenoidal anatomy on CBCT: internal carotid artery, optic nerve, foramen rotundum, vidian canal, and intersphenoid sinus septum.

OBJECTIVE: To assess individual and combined cone-beam CT (CBCT) relationships of the internal carotid artery (ICA), foramen rotundum (FR), optic nerve (ON), vidian canal (VC) and intersphenoid sinus septum (ISS), and to characterise bilateral symmetry across increasing anatomical dimensionality in a single patient sample. METHODS: CBCT studies from 153 patients (306 sides) were analysed. Coding was distributed between two primary observers, each coding a non-overlapping portion of the sample, and a senior anatomist re-coded all sides; agreement with the senior anatomist was assessed for each categorical variable. ICA, ON, FR, and VC types, as well as ISS pattern and termination, were coded using published categorical schemes. Categorical associations were tested with chi-square or Fisher's exact tests. RESULTS: Across 306 sides, the most frequent categories were ICA type 1 (36.6%), type 3 (36.3%), FR type II (70.3%), ON DeLano type 1 (54.2%), and VC type 2 (51.0%). The number of distinct configurations rose with dimensionality, reaching 41 four-variable phenotypes. Bilateral symmetry declined with increasing dimensionality (single-variable symmetry 63.4-80.4%; all-four symmetry 27.5%), and the ISS pattern was single in most patients (75.2%). ICA-involving posterior septal termination occurred in 43.1% of patients. CONCLUSIONS: In this CBCT sample, perisphenoidal categorical anatomy was heterogeneous, and the proportion of patients with matching right and left configurations decreased as more variables were combined, as expected for exact categorical agreement. Agreement between each primary observer and the senior anatomist supported the reliability of the coding, and bilateral ICA-attached septal termination was uncommon (5/153, 3.3%).