The “suprasellar notch,” or the tuberculum sellae as seen from below: definition, features, and clinical implications from an endoscopic endonasal perspective

Abstract

The tuberculum sellae is a bony elevation ridge that lines up the anterior aspect of the sella, dividing it from the chiasmatic groove. The recent use of the endoscopic endonasal transtuberculum approach has provided surgeons with a method to reach the suprasellar area, offering a new surgical point of view somehow "opposite" of this area. The authors of this study aimed to define the tuberculum sellae as seen from the endoscopic endonasal view while also providing CT-based systematic measurements to objectively detail the anatomical features of such a structure, which was renamed the "suprasellar notch." The authors analyzed routine skull CT scans from 24 patients with no brain pathology or fractures and measured the interoptic distance at the level of the limbus sphenoidale, the chiasmatic groove sulcal length and width, and the angle of the suprasellar notch. Indeed, the suprasellar notch was defined as the angle between 2 lines, the first passing through the tuberculum sellae midpoint and perpendicular to the cribriform plate, and a second line passing between 2 points, the midpoints of the limbus sphenoidale and the tuberculum sellae. Moreover, the authors performed on 15 cadaveric heads an endoscopic endonasal transplanum transtuberculum approach with the aid of a neuronavigator to achieve a step-by-step comparison with the radiological data. The whole CT scanning set was statistically analyzed to determine the statistical interdependency of the suprasellar notch angle with the other 3 measurements, that is, the sulcal length at the midline, the interoptic distance at the optic canal entrance, and the interoptic distance at the limbus. Based on the endoscopic endonasal view and CT imaging analysis, the authors identified a certain anatomical variability and thus introduced a new classification of the suprasellar notch: Type I, angle < 118°; Type II, angle of 118°-138°; and Type III, angle > 138°. They then analyzed the surgical implications of the endoscopic endonasal approach to the suprasellar area, which could be affected by each of these structural types. The new classification identifies 3 different types of suprasellar notch and, accordingly, their surgical relevance. Above all, the authors found that the different types of suprasellar notch can affect the osteodural defect reconstruction technique, namely the positioning/wedging of the buttress in the extradural space. A precise endoscopic anatomical knowledge of the neurovascular and bony relationships--especially in cases of a less pneumatized sphenoid sinus--is crucial when approaching the anterior skull base via a transtuberculum transplanum route.