Grasso, Giovanni

OBJECTIVE Lesions of the cerebellopontine angle (CPA) and petroclival region represent a challenging surgical target due to the complex anatomy of the involved neurovascular structures. In this scenario, cranial nerve (CN) VI is particularly exposed to potential injuries due to its deep-seated location and absence of a bony foramen that serves as a reference of its most distal cisternal point, especially when it is encased or displaced by large lesions. This study aimed to provide reliable operative guidance for preventing injuries to CN VI during the retrosigmoid approach to address CPA and petrotentorial lesions. METHODS Four formalin-fixed, latex-injected anatomical specimens were dissected to highlight and investigate the relevant anatomy of the CPA and petroclival region during the retrosigmoid approach. Additionally, 50 sides of noninjected formalin-fixed specimens were dissected for morphometric evaluation. Correlations between the petrotentorial junction (PTJ), porus acusticus (PA), and trigeminal impression (TI) with the entry point of CN VI into Dorello’s canal were evaluated. An illustrative clinical case and a 3D anatomical model generated through the photogrammetry scanning technique were described. RESULTS In the sagittal plane, CN VI entrance into Dorello’s canal was found in a trajectory parallel to the PTJ, passing through the inferior aspect of the PA and 21.5 ± 1.3 mm anteriorly. In the coronal plane, the entry point of CN VI into Dorello’s canal was estimated at 6.2 ± 1.2 mm from the anterior edge of the TI in a trajectory perpendicular to the PTJ in 47 (81%) specimens. CONCLUSIONS The obtained results demonstrated two surgical strategies to locate Dorello’s canal within the retrosigmoid route: 1) approximately 20 mm anterior along the inferior edge of the PA parallel to the PTJ; and 2) approximately 6 mm inferior to the anterior edge of the TI, perpendicular to the PTJ. The defined operative strategies provide reliable anatomical guidance to locate the entrance of CN VI into Dorello’s canal within the retrosigmoid route, potentially reducing the risk of abducens nerve palsy and improving patient outcomes.

BACKGROUND AND OBJECTIVES: The lateral transorbital approach (LTOA) has gained increased recognition, but there is still a paucity of data on its effectiveness and advantages compared with the LTOA with lateral orbitotomy, herein denoted as the lateral orbital wall approach (LOWA). The aim of this study was to provide an anatomical reappraisal and the authors' clinical experience to compare the 2 approaches to the orbit and middle cranial fossa (MCF). METHODS: Eight latex-injected cadaveric specimens were used to perform LTOA and LOWA. The operative depth of each approach to key anatomical landmarks was measured. Fifty high-resolution computed tomography studies were reviewed to calculate the operative angles. We reviewed 40 consecutive cases treated with LTOA and LOWA at our institution. RESULTS: Compared with the LTOA, the LOWA provided shorter operative depths to the optic foramen ( P < .05), foramen ovale ( P < .05), and to the junction eyeball-cranial nerve II ( P = .13). It also offered better access to the anterior aspect of the orbit with less orbital content retraction. The LTOA and LOWA provided different operative angles to key anatomical landmarks in the orbit and MCF ( P < .05). In our chart review, 31 patients underwent the LTOA, whereas 9 underwent the LOWA to treat orbital and MCF lesions. Patients undergoing LOWA experienced postoperative complications related to periorbital nerves, such as frontalis palsy (n = 1) and supraorbital neuralgia (n = 1). Patients undergoing LTOA were more prone to complications associated with intraorbital manipulation (n = 4), including diplopia and ptosis. CONCLUSION: Our data suggest that the LTOA can be an effective surgical strategy for addressing orbital apex and MCF lesions. Although the LOWA provides access to the aforementioned areas, it may be more suitable for anterior orbital lesions that require direct access with wider entry exposure and extensive orbital content manipulation.

OBJECTIVE Advances in surgical technology and microneurosurgery have led to increased utilization of so-called minimally invasive approaches, including the supraorbital eyebrow (SE) and minipterional (MPT) approaches for lesions involving the interpeduncular region. This study aimed to describe and compare anatomical landmarks, along with highlighting the advantages and disadvantages of the SE and MPT approaches to the interpeduncular region. METHODS Ten formalin-fixed, latex-injected cadaveric specimens were used to perform bilateral SE and MPT approaches to the interpeduncular region. The operative depth of each approach to key anatomical landmarks was measured. Forty-five axial thin-slice computed tomography studies were reviewed to calculate the operative angles, with consideration of the midline as a reference. A 3D interactive anatomical model generated through the photogrammetry scanning technique was described. RESULTS The depths of the operative corridors of the SE and MPT approaches to the interpeduncular fossa were 83.4 ± 1.8 mm and 67.7 ± 3.2 mm, respectively (p < 0.001). The mean angle of the MPT approach to the interpeduncular fossa was significantly wider than the one provided by the SE approach (39.9° ± 5.1° vs 28.4° ± 3.6°, p < 0.001). The interpeduncular region can consistently be accessed through the carotid-oculomotor triangle with the SE approach, as well as with the MPT approach. Furthermore, the SE route offered adequate access to the interpeduncular fossa through the opticocarotid triangle. The MPT route provided direct access to the upper prepontine cistern and anterior mesencephalic zone (AMZ). CONCLUSIONS The MPT approach provides a wider and shorter operative corridor and can be employed for lesions in the interpeduncular region with extension to the prepontine cistern and ventrolateral midbrain lesions requiring access through the AMZ. The SE approach is better suited for ventromedial midbrain lesions requiring access via the interpeduncular fossa safe entry zone. Additional studies analyzing these approaches in a clinical setting will help to delineate their reliability and efficacy.