Systematic anatomical validation of the endoscopic mononostril transethmoid-paraseptal approach to the central skull base.

Introduction: The endoscopic transsphenoidal approach is the standard technique to remove central skull base lesions; however, binostril modifications often require extensive intranasal dissection resulting in sinonasal morbidity. Research question: The transethmoid-paraseptal approach (TPA) is a mononostril alternative designed to preserve sinonasal function while maintaining adequate surgical exposure. Its systematic anatomical and radiological validation is lacking. Materials and methods: The TPA was performed on 19 cadaveric specimens to identify anatomical landmarks and assess reproducibility. Based on the dissections, a surgical checklist was developed. Cone-beam CT scans of 43 patients and 9 further cadaveric heads (total: 104 sides) were analyzed using the 3D-Slicer software to identify anatomical variants influencing the approach. Results: The TPA corridor was successfully established in all cadaveric cases. Consistent identification of key landmarks-e.g. uncinate process, ethmoid bulla, sphenoid rostrum, and sphenoid sinus-was achieved in 100% of specimens, except for one undeveloped ethmoid bulla. Relevant anatomical variants included: fusion of the ethmoid bulla with the basal lamella of the middle turbinate (62.6%), nasal septal deviation (36.6%), posterosuperior ethmoid (Ónodi-) cell (12.2%), conchal type sphenoid sinus (2.8%), maxillary sinus hypoplasia (0.8%). All variants were detectable on preoperative imaging and did not preclude the approach. A conversion to binostril surgery was not required. Discussion and conclusion: The TPA is a reproducible, anatomically reliable mononostril corridor to the central skull base. Preoperative CT analysis allows identification of anatomical variants that may influence surgical orientation. Further clinical studies are required to compare the surgical outcomes and different transnasal techniques.