Anatomical study in exposed area and operating space of extended endonasal approach to the ventral region of cranio-cervical junction

Abstract

Objective To explore the scope, feasibility and indications of extended neuroendoscopic endonasal approach to reveal the region of cranial-cervical junction. Methods Ten (20 sides) intact frozen adult cadaveric heads were used to simulate the extended neuroendoscopic endonasal approach to remove the anterior tubercle of atlas, part of the atlas anterior arch, odontoid and part of the slope. In the cranial-cervical junction area, we observed the exposed range and measured the distance from the nostril to the anterior tubercle of atlas, the height and width of the anterior arch of the atlas, the distance of bilateral medial margin of occipital condyle, the distance of bilateral medial margin of the foramen lacerum, the vertical distance from the occipital condyle to the homolateral foramen lacerum, and the height, anteroposterior diameter and transverse diameter of the odontoid. Results The exposed range of the extended neuroendoscopic endonasal approach was as follows: when the lesion was located at the foramen magnum, the medial margin of the occipital condyle was the boundary of both sides, the root of the odontoid was the lower boundary, and the lower edge of the occipital bone was the upper boundary. When the lesion was located at the region of cranial-cervical junction, the upper edge of the foramen lacerum on both sides was the upper boundary, and the foramen lacerum and the outer edge of the occipital condyle were the boundaries of both sides of the bone window. By measurement, the distance from the nostril to the anterior tubercle of atlas was 8.9-9.7 cm, with an average of 9.3±0.3 cm. The height of the anterior arch of the atlas was 2.3-3.0 cm, with an average of 2.7±0.3 cm; the width was 1.5-2.0 cm, with an average of 1.8±0.2 cm; the distance of bilateral medial margin of occipital condyle was 1.5-2.0 cm, with an average of 1.8±0.2 cm; the distance of bilateral medial margin of the foramen lacerum was 2.1-2.9 cm, with an average of 2.4 ±0.3 cm; the vertical distance from the occipital condyle to the homolateral foramen lacerum was 1.6-2.2 cm, with an average of 1.9±0.3 cm; the height of the odontoid was 0.9-1.3 cm, with an average of 1.1±0.2 cm, its length was 0.8-1.3 cm, with an average of 1.1±0.2 cm; the transverse diameter of the dentate was 0.9-1.2 cm, with an average of 1.0±0.1 cm.The maximum exposed area of cranio-cervical junction was 6.4-9.8 cm2, with an average of 8.6±1.6 cm2. Conclusion The extended neuroendoscopic endonasal approach with removal of the anterior tubercle of atlas and part of the atlas anterior arch could effectively reveal the cranial-cervical junction area which is suitable for the treatment of odontoid deformity, skull base depression and atlantoaxial joint dislocation as well as resection of epidural tumors in the cranial-cervical junction and ventral and ventral midline tumors. Key words: Natural orifice endoscopic surgery; Anatomy; Cranio-cervical junction; Extended endonasal approach