The Anatomical Research Of The Extended Endoscopic Endonasal Approach To The Clivus Region

Objective: To study the anatomy of the clivus and adjacent structures by cadaveric specimens and dry skulls, and provide the anatomical parameters and morphological basis for clinical surgeons in the endoscopic surgery via the extended endoscopic endonasal approach.Methods: Ten cadaveric heads and 20 dry skulls were dissected using the surgical microscope, endoscope and measurement of the key anatomical landmark on the clivus of osseous skull base.(1) 5 cadaveric specimens were sectioned in the coronal plane perpendicular to the hard palate, dissected under the surgical microscope to observe anatomical feature of the endonasal approach to the clivus region.(2) The extended endoscopic endonasal approach was performed on 5 cadaveric specimens to understand anatomical relationship and feature around the clivus region under the endoscopic view.(3)20 dry skulls were used to measure the distance from paired structures of skull base to the median line: vidian canal, jugular foramen, external orifice of the hypoglossal canal,occipital condyle, external orifice of the carotid canal, as well as the distance from the dorsum sella to the anterior margin of the foramen magnum, distance from spheno-occipital synchondrosis to the anterior margin of the foramen magnum, distance from the spheno-occipital synchondrosis to the pharyngeal tubercle, and distance from the pharyngeal tubercle to the anterior margin of the foramen magnum.Results:(1) Through the cadaveric study with microsurgical and endoscopic approach to the clivus region, The posterior opening of the vidian nerve located at the floor of the sphenoid sinus wall and pharyngeal tubercle were determined to be the important extracranial anatomical landmarks for extended endoscopic endonasal approach to the clivus.(2) With the extended endoscopic endonasal approach, we can expose the ventral side of brain stem from interpeduncal fossa to the foramen magnum and upper, middle, and lower neurovascular complexes.(3) The clivus region, formed by the sphenoid body and the clival part of occipital bone, was situated between the dorsum sellae and the anteriormargin of the foramen magnum. The petroclival fissure, which lies along the lateral edge of the clivus, separates the occipital bone and the petrous part of the temporal bone. The distance between the dorsum sellae and the anterior margin of the foramen magnum was46.50 ± 4.05 mm. The distance between the spheno-occipital synchondrosis and the anterior margin of the foramen magnum was 26.26±4.00 mm. The distance between the spheno-occipital synchondrosis and the pharyngeal tubercle was 20.01 ± 0.50 mm. The distance between the pharyngeal tubercle and the anterior margin of the foramen magnum was 14.41±0.73 mm. The distance between paired structures and the median line was as follows: vidian canal was 13.14±0.37 mm on the left and 13.05±0.33 mm on the right,jugular foramen was 28.26 ± 0.40 mm on the left and 28.08 ± 0.35 mm on the right;external orifice of the hypoglossal canal was 18.44±0.68 mm on the left and 18.30±0.60 mm on the right; occipital condyle was 8.74±0.11 mm on the left and 8.66±0.15 mm on the right; external orifice of the carotid canal: 28.80±0.69 mm on the left and 29.15±0.78 mm on the right.Conclusions:(1) The clivus is divided into upper, middle, and lower thirds by two intracranial landmarks: the dural pori of the abducens nerves and the dural meati of the glossopharyngeal nerves. The classification method of the clivus fits with the concept of upper, middle, and lower neurovascular complexes in the posterior cranial fossa.(2) The extended endoscopic endonasal approach can be tailored to deal with the local lesions involving the clivus and adjacent posterior cranial fossa structures.(3) The posterior opening of the vidian nerve located at the floor of the sphenoid sinus wall and pharyngeal tubercle were determined to be the important extracranial anatomical landmarks for extended endoscopic endonasal approach to the clivus.