Anatomical investigation of the contribution of anterior petrosectomy to ventral brain stem access with cadaver dissections in the combined transpetrosal approach

OBJECTIVE: Surgical access to the ventral part of the brainstem is technically very difficult and anatomically complex due to the important neural and vascular structures involved in and around the corridor opened to reach the region. Combined transpetrosal approach is a surgical approach performed by combining retrolabyrinthine mastoidectomy, supra-infratentorial craniotomy and anterior petrosectomy, and tentorium resection to access the petroclival region and brainstem. Combined transpetrosal approach provides ventrolateral access to brainstem regions between the n. oculomotorius and the foramen jugulare; however, there are some factors that limit ventral vision. By adding various modifications to the approach, access to the ventral brainstem and medial clivus can be increased. In this study, we aimed to examine the anatomical basis of the contribution of various modifications added to the combined transpetrosal approach to access to the ventral brainstem. MATERIAL AND METHODS: In this study, which was performed on a total of 6 (12 sides) human cadavers at Istanbul University - Cerrahpasa, Cerrahpasa Medical Faculty, Department of Anatomy, Cadaver Dissection Laboratory and Istanbul University - Cerrahpasa, Cerrahpasa Medical Faculty, Department of Neurosurgery, Microsurgery Neuroanatomy Laboratory, the cadavers were positioned appropriately and then combined transpetrosal approach and additional modifications were carried out step by step. Each stage applied was photographed and the data of each stage was recorded. The contributions obtained through additional modifications were evaluated. RESULTS: The addition of a combined transpetrosal approach, partial and total labyrinthectomy, contributed to the exposure of the fossa cranii posterior. Both transcochlear and preauricular subtemporal infratemporal fossa approach modifications provided access to the canalis caroticus and contributed to additional pars petrosa resection anterior to the meatus acusticus internus and access to the clivus. CONCLUSION: By adding partial or total labyrinthectomy modifications and trancochlear modification to the combined transpetrosal approach, an additional posterior petrosectomy can be performed to increase ventral access to the fossa cranii posterior, especially the sulcus pontomedullaris, superior part of the medulla oblongata, and the vertebrobasilar junction. Additional anterior petrosectomy performed by accessing the canalis caroticus, either through transcochlear modification or by modification of the preauricular subtemporal infratemporal fossa approach, can increase access to both the ventral brainstem and the medial clivus. In addition, these modifications provide the opportunity for partial clivectomy, thus increasing ventral exposure. Additional petrosectomy and clivectomy increase ventral exposure to the brainstem. March 2024, 76 pages. Keywords: os temporale, pars petrosa, anterior petrosectomy, posterior petrosectomy, combined transpetrosal approach