Leonel, Luciano

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.

ABSTRACT Objective Sacrifice of pterygopalatine fossa (PPF) neurovascular structures during endoscopic endonasal transpterygoid approach (EETPA) may impact a patient's comorbidity. We present anatomical and surgical techniques for maximizing PPF transposition while preserving its neurovascular structures through orbito‐pterygo‐sphenoidal (OPS) ligament release and descending palatine canal (DPC) decompression. Methods The EETPA was performed on six specimens. Two measurements were obtained to assess PPF transposition: (1) Inferior transposition (distance between the superior margins of the base of the pterygoid process and PPF); (2) lateral transposition (distance from Eustachian tube lateral margin to PPF medial margin). Results After incising the OPS ligament, a mean gain of PPF inferior transposition of 7 mm (4–11 mm, p = 0.03) was observed, with a total inferior transposition of 12 mm (6–15 mm). Subsequently, the posterior half of the inferior turbinate was removed and the DPC was decompressed, with a mean gain of PPF lateral transposition of 12 mm (range 8–15 mm, p = 0.01). Conclusion The OPS ligament release offers a significant advantage for the PPF inferior transposition, allowing access to the inferolateral recess of the sphenoid sinus, cavernous sinus, and paramedian middle cranial fossa, while the DPC decompression provides a significant advantage for the PPF lateral transposition, granting access to the Eustachian tube and ITF. Level of Evidence N/A.

BACKGROUND AND OBJECTIVE: In skull base surgery, endoscopic endonasal approaches require precise evaluation of the area of exposure and the maneuverability provided by each approach. Current neuroanatomical methodologies for quantifying these parameters primarily rely on computed tomography (CT) scans and neuronavigation systems, which entail significant financial investment. The aim of this study was to develop and validate an innovative, cost-effective methodology using an endoscopic photogrammetric model to measure the exposure area and maneuverability in endoscopic endonasal approaches, offering an accessible alternative to existing techniques. METHODS: Six cadaveric specimens were used to validate the accuracy of endoscopic photogrammetric measurements by comparing them with direct measurements. Subsequently, the exposure area, angle of attack, and surgical freedom were analyzed for 3 endoscopic approaches to the parasellar region: contralateral transmaxillary, single-nostril, and double-nostril approaches. RESULTS: Photogrammetric measurements demonstrated a high level of concordance with direct cadaveric measurements, with a mean difference of 0.02 mm as shown in the Bland-Altman plot. In addition, measurements obtained in comparative analysis describing the exposure area and maneuverability of 3 endoscopic approaches were congruent with those reported in existing literature derived using CT scans and neuronavigation systems. CONCLUSION: To our knowledge, this study is the first to validate endoscopic photogrammetric models as a measurement tool in neuroanatomy. Performing direct measurements on 3D models might eliminate the necessity of expensive CT and neuronavigation systems for volumetric quantification. Our cost-effective methodology allows for the widespread democratization of anatomical quantification within skull base neuroanatomy.

Summary: Anatomy is a critical component of surgical training; however, traditional resources—such as Netter’s Surgical Anatomy , Gray’s Anatomy , and anatomy applications—often fall short in delivering surgically relevant, 3-dimensional (3D) perspectives of facial anatomy. Although cadaveric dissection remains a valuable teaching tool, its accessibility is limited by cost, ethical concerns, and the lack of structured curricula, making it less feasible for ongoing surgical education. To address these limitations, this article introduced a novel educational approach that integrates 3D photogrammetry and virtual reality technology into the surgical anatomy curriculum for craniofacial and aesthetic surgery. Six fresh cadaveric specimens were meticulously dissected by a plastic surgeon to illustrate the intricate layered anatomy of the face and neck. At each stage of the dissection, a photogrammetry technique was used to capture 360-degree images using 5 digital single-lens reflex cameras alongside a 3D handheld camera. This approach not only ensured high-quality imaging but also facilitated the creation of detailed, lifelike virtual 3D models, enhancing the understanding of facial and neck anatomy within a surgical context. Additionally, we present some technical refinements of the 3D volume renderings to capture precise anatomical details during our dissections. Preliminary results from the use of this technology in anatomy courses and workshops indicated trainee engagement, a clearer grasp of the spatial anatomical relationships, and greater confidence in applying this knowledge to hands-on surgical procedures.

BACKGROUND AND OBJECTIVES: Photogrammetry application is rapidly growing within the anatomical field as a new technique, underlining the need for the development of a comprehensive step-by-step methodology and guide to facilitate the pursuit of high-definition photogrammetry. Therefore, the aim of this study was to describe 2 photogrammetry techniques and their step-by-step from positioning and preparing the specimens for photodocumentation to the final 3-dimensional (3D) model displayed on online platforms. METHODS: Two dry skulls, 2 embalmed brains, and 30 embalmed and latex-injected heads were used for the study, rendering a total of 130 3D models. The specimens were placed on a turntable and photodocumented using a digital single-lens reflex camera or smartphone, and the key steps and notes were methodically described. RESULTS: The photogrammetry technique using either a digital single-lens reflex camera or smartphone required images captured in 3 different steps: overview images, close range photographs, and images of depth-located structures. All images were then upload to Agisoft Metashape software, postprocessed and rendered into the final 3D model and displayed using Sketchfab ® . CONCLUSION: This article provided a detailed description of a high-resolution photogrammetry scanning technique, highlighting the advantages and relevance of acquiring 3D models through mobile devices to demystify and clarify the technique to enhance the experience in clinical and neuroanatomical application.

Abstract Cadaveric dissections, which are considered the most realistic model to study neuroanatomy, are expensive and not readily available in all centers. Given the surge of technological advances, incorporation of three‐dimensional (3D) scanning technologies and 3D models has gained popularity, both in the educational and clinical settings. We present our institutional experience in creating high‐fidelity neuroanatomical 3D models using three 3D scanning techniques: structured light 3D scanning, “manual” photogrammetry with a single DSLR camera, and “automatic” photogrammetry using a scanner equipped with five vertically arranged DSLR cameras and an automatic turntable within a square box. A survey study was conducted with 20 neurosurgical residents to assess the quality of the three resulting 3D models. In the study, “manual” photogrammetry was determined to be the most cost‐effective technique, while “automatic” photogrammetry was the most time‐effective and user‐friendly technique. The best visual quality was obtained using “manual” photogrammetry, as determined from survey results of 20 neurosurgical residents. While structured light 3D scanning had the lowest quality of resolution of the texture map, this technique was the most accurate to use for determining measurements, with a fixed accuracy of 0.05 mm. Overall, “manual” photogrammetry can allow for the most detailed 3D models and is the most cost‐effective strategy, while structured light 3D scanning is most suitable for obtaining clinically relevant measurements given the high degree of structural accuracy. Alternatively, “automatic” photogrammetry can serve as a hybrid between obtaining relatively high‐quality models in a time‐effective and user‐friendly manner.

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.