Anatomical impact of C1 transverse process resection on inferior and inferolateral exposure at the craniocervical junction: a cadaveric study.

BACKGROUND: Surgical exposure of the craniocervical junction (CCJ) is challenging because of the narrow osseous corridor and complex neurovascular anatomy. Although the far lateral approach is well established, the relative anatomical contribution of sequential osseous modifications used in far lateral surgery remains incompletely understood. This study aimed to provide a stepwise anatomical comparison of retrosigmoid, far lateral, and extended far lateral approaches, focusing on neurovascular exposure before C1 transverse process resection. METHODS: Four formalin-fixed, silicone-injected adult human cadaveric heads (eight sides) were dissected. Retrosigmoid, far lateral, and extended far lateral approaches with C1 transverse process resection were sequentially performed. Exposure of the lower cranial nerves (CN), vertebral artery (VA), and inferior surgical corridor was qualitatively assessed under operative microscopy. RESULTS: The retrosigmoid approach provided limited inferior exposure due to the foramen magnum. Far lateral exposure with condylar drilling and C1 laminectomy provided greater inferior reach, allowing visualization of the VA V3 segment and extracranial portions of the lower CNs. Notably, substantial exposure of the jugular foramen-C1 interval was achieved before C1 transverse process resection. Additional C1 transverse process resection mainly enhanced inferolateral working space by permitting wider mobilization of the V3 segment and lower CNs, with only limited additional contribution to caudal exposure. CONCLUSION: C1 laminectomy is the key step for increasing inferior reach at the CCJ, whereas C1 transverse process resection primarily improves inferolateral maneuverability and VA mobilization. Because substantial exposure is already achieved after condylar drilling and C1 laminectomy, transverse process resection should be applied selectively rather than routinely, particularly in lesions requiring extensive VA mobilization or inferolateral exposure.