Peris‐Celda, Maria

BACKGROUND AND OBJECTIVES: Contralateral transfalcine approaches are widely used for interhemispheric/mesial cortical pathologies, even those extending beyond 2 cm lateral from the midline. Nevertheless, the superior limit of contralateral exposure through this approach is not defined. This anatomic study aims to characterize the maximal superior and lateral limits of contralateral exposure using a contralateral transfalcine approach. METHODS: Interhemispheric approaches in the anterior, middle, and posterior-thirds of the interhemispheric fissure were performed in 10 cadaveric head specimens. Rectangular falcine incisions were made and carried maximally superiorly. The contralateral hemisphere was maximally laterally resected from the superior point of visualization down to the level of the corpus callosum. Distances between the most superior point of visualization of the contralateral hemisphere and the superficial point of its cortex and between the midline and the most lateral point of visualization at the level of the corpus callosum were measured and are reported as averages. RESULTS: At the anterior-third of the interhemispheric fissure, the superior point of visualization was 4.8 mm inferior to the cortex. The lateral distance of visualization at the genu of the corpus callosum was 22.9 mm. At the middle-third, the superior point of visualization was 9.7 mm inferior to the cortex. The lateral distance visualized at the body of the corpus callosum was 22.4 mm. At the posterior-third, the superior point visualization of the mesial contralateral hemisphere was 12.6 mm inferior to the cortex. The lateral distance visualized at the splenium of the corpus callosum was 21.3 mm. CONCLUSION: Using the contralateral transfalcine approach, the superior limit of contralateral exposure progressively decreases more posteriorly along the interhemispheric corridor—ranging from 4.8 mm inferior to the cortex in the anterior-third to 12.6 mm inferior to the cortex in the posterior-third. The contralateral optimal view of exposure increases deeper along the interhemispheric corridor.

BACKGROUND AND OBJECTIVES: Contemporary skull base surgeons must understand transcranial and endoscopic endonasal approaches to the petrous apex (PA). We provide an anatomic overview and comparison of main approaches to the PA through illustrative anatomic dissections. METHODS: On 10 sides of 5 specimens, transcranial approaches to the PA including the anterior petrosal, transcochlear, and retrosigmoid with suprameatal extension were performed. For endoscopic endonasal approaches, the transclival approach was performed in the midline of 5 specimens and its contralateral transmaxillary extension was performed on 10 sides. RESULTS: The anterior petrosal approach offers an anterolateral view of the PA bounded by petrous ridge posteromedially, internal auditory canal posterolaterally, greater superficial petrosal nerve anterolaterally, and lateral boundary of cranial nerve V, the Gasserian ganglion, and V3 anteromedially; it exposes the middle fossa and, once the PA is removed, the superomedial cerebellopontine angle. The transcochlear approach affords a lateral view of the PA defined medially and inferiorly by inferior petrosal sinus, posteriorly by posterior fossa dura, anteriorly by the petrous internal carotid artery, and superiorly by the superior petrosal sinus and middle fossa dura. Through a retrosigmoid approach, the PA is bounded by the superior petrosal sinus superiorly, the sagittal plane of cranial nerve VI medially, and the axial and sagittal plane of the internal auditory canal porus inferiorly and laterally, respectively. It affords a panoramic view of the posterior fossa and access to Meckel's cave after PA drilling. Endoscopic endonasal approaches target the anteromedial PA, and it is demarcated by a triangle consisting of cranial nerve VI posterolaterally, the paraclival segment of the internal carotid artery anteriorly, and the petroclival synchondrosis inferiorly and medially. The addition of the contralateral transmaxillary approach enhances lateral access up to the internal auditory canal. CONCLUSION: We provide a comprehensive overview of the main approaches to the PA through illustrative anatomic dissections and representative cases.