An Endoscopic Endonasal Nasopharyngectomy with Posterolateral Extension

Background Invasion depth influences the choice for extirpation of nasopharyngeal malignancies. This study aims to validate the feasibility of endoscopic endonasal resection of lesions with a posterolateral invasion. As a secondary goal, the study intends to propose a classification system of endoscopic endonasal nasopharyngectomy determined by the depth of posterolateral invasion. Methods Eight cadaveric specimens (16 sides) underwent progressive nasopharyngectomy using an endoscopic endonasal approach. Resection of the torus tubarius, Eustachian tube (ET), medial pterygoid plate and muscle, lateral nasal wall, and lateral pterygoid plate and muscle were sequentially performed to expose the fossa of Rosenmüller, petroclival region, parapharyngeal space (PPS), and jugular foramen, respectively. Results Technical feasibility of endonasal nasopharyngectomy toward a posterolateral direction was validated in all 16 sides. Nasopharyngectomy was classified into four types as follows: (1) type 1: resection restricted to the posterior or superior nasopharynx; (2) type 2: resection includes the torus tubarius which is suitable for lesions extended into the petroclival region; (3) type 3: resection includes the distal cartilaginous ET, medial pterygoid plate, and muscle, often required for lesions extending laterally into the PPS; And (4) type 4: resection includes the lateral nasal wall, pterygoid plates and muscles, and all the cartilaginous ET. This extensive resection is required for lesions involving the carotid artery or extending to the jugular foramen region. Conclusion Selected lesions with posterolateral invasion into the PPS or jugular foramen is amenable to a resection via expanded endonasal approach. Classification of nasopharyngectomy based on tumor depth of posterolateral invasion helps to plan a surgical approach.

Study of comparative surgical exposure to the petroclival region using patient-specific, petroclival meningioma virtual reality models

OBJECTIVE Despite advancement of surgical techniques, the attachments of petroclival meningiomas near the central clival depression (CCD) remain difficult to visualize. With existing methods, the amount of tumor near the CCD that is inaccessible through various approaches cannot be compared. Tumors distort the brainstem, changing the size of the operative corridor for some but not all approaches; therefore, using cadavers with normal posterior fossae makes it impossible to compare different approaches to the tumor. The authors used virtual reality (VR) models created from the imaging data of patients to compare various surgical approaches that have otherwise been incomparable in previous studies. METHODS CT and MRI data obtained in 15 patients with petroclival meningiomas were used to create anatomically accurate 3D VR models. For each model, various surgical approaches were performed, and the surgical freedom to 6 targets of the regions were measured. Furthermore, portions of the tumor that were visually blocked by the brainstem or bony structures were segmented and recorded as blinded volumes for comparison. RESULTS The extended retrosigmoid approach generated excellent exposure of the petroclival region, but for most specimens, there was inaccessible tumor volume adjacent to the brainstem (mean 641.3 mm3, SE 161.8). In contrast, the brainstem sides of the tumors were well-visualized by all the transpetrosal approaches. The blinded volume of the tumor was largest for the retrolabyrinthine approach, and this was statistically significant compared with all other approaches (mean 2381.3 mm3, SE 185.4). CONCLUSIONS The authors performed a novel laboratory study by using patient CT and MRI data to generate 3D virtual models to compare surgical approaches. Since it is impossible to perform various approaches in separate surgeries in patients for comparison, VR represents a viable alternative for such comparative investigations.

Use of Neuroanatomic Knowledge and Neuronavigation System for a Safe Anterior Petrosectomy

Introduction: The petroclival region is among the most challenging anatomical areas to deal with in skull base surgery. Drilling of the anterior part of the petrous bone during the anterior transpetrosal approach involves the risk of injury of the cochlea, superior semicircular canal, internal carotid artery, and internal auditory canal. A thorough understanding of the microneurosurgical anatomy of this region is mandatory to execute the transpetrosal approaches, decreasing the risk of complications. The aim of this study is to describe the anatomical structures of the petroclival region, highlighting the importance of neuronavigation for safe performance of the anterior transpetrosal approach. Methods: Three adult cadaveric human heads were formalin-fixed and injected with colored silicone. They underwent an axial 1 mm slab CT scan, which was used for neuronavigation during the surgical approaches. The anterior petrosectomy was performed with the aid of neuronavigation during the drilling of the petrous bone. The surgical management of a patient harboring a petroclival meningioma, operated on using an anterior transpetrosal approach, was reported as an illustrative case. Results: The anterior petrosectomy was completed accurately with wide exposure of the surgical target without injuring the cochlea and other structures in all three cadaveric specimens. In the surgical case, no approach-related complications occurred, and a gross total resection of the tumor was achieved. Conclusions: Deep knowledge of the location and relationships of the vital elements located within the temporal bone, along with the use of neuronavigation, are the key aspects to perform the anterior transpetrosal approach safely, reducing the risk of complications.

Morphometric Study of the Posterior Fossa: Identification of Practical Parameters for Tailored Selection of Surgical Routes to the Petroclival Region

Introduction The petroclival region is an integral part of the skull base. It can harbor different pathologies and provides access to the petroclival junction and cerebellopontine angle. We present the results of the morphometric analysis of the posterior fossa and a prediction model to enable skull base surgeons to choose an optimal surgical corridor considering patient's bony anatomy. Methods Ninety patients (14 to assess interobserver reliability) with temporal bone computed tomography were selected. Exclusion criteria included patients <18 years of age, radiographic evidence of trauma, infection, or previous surgery. The images were analyzed using OsiriX MD (Bernex, Switzerland). We recorded clival length, vertical angle, and surface area, and petroclival angle, petrous apex, and translabyrinthine corridors volume. Results The average age was 49.5 years (55%) for males. The mean clival length and surface areas were 44.2 mm (standard deviation [SD] ± 4.1) and 8.1 cm2 (SD ± 1.3). The mean petrous apex and translabyrinthine corridors volumes were 2.2 cm3 (SD ± 0.6) and 10.1 cm3 (SD ± 3.7). The mean petroclival angle at the internal auditory canal (IAC) was 154.9 degrees (SD ± 9). The clival length correlated positively with clival surface area (rho = 0.6, p <0.05), petrous apex volume (rho = 0.3, p < 0.05), and translabyrinthine volume (rho = 0.3, p < 0.05). Conclusion The petroclival region is complex and with high variability of surgical significance. The use of preoperative measurements of the clival length and petroclival angle as part of surgical planning that could help the surgeon to choose an optimal surgical corridor by overcoming the anatomical variability elements.

Anatomical Limits of the Endoscopic Contralateral Transmaxillary Approach to the Petrous Apex and Petroclival Region

Objectives This study aimed to establish the anatomical landmarks for performing a contralateral transmaxillary approach (CTM) to the petrous apex (PA) and petroclival region (PCR), and to compare CTM with a purely endoscopic endonasal approach (EEA). Design EEA and CTM to the PA and PCR were performed bilaterally in eight human anatomical specimens. Surgical techniques and anatomical landmarks were described, and EEA was compared with CTM with respect to ability to reach the contralateral internal acoustic canal (IAC). Computed tomographic scans of 25 cadaveric heads were analyzed and the “angle” and “reach” of CTM and EEA were measured. Results Entry to the PA via a medial approach was limited by (1) abducens nerve superiorly, (2) internal carotid artery (ICA) laterally, and (3) petroclival synchondrosis inferiorly (Gardner's triangle). With CTM, it was possible to reach the contralateral IAC bilaterally in all specimens dissected, without dissection of the ipsilateral ICAs, pterygopalatine fossae, and Eustachian tubes. Without CTM, reaching the contralateral IAC was possible only if: (1) angled endoscopes and instruments were employed or (2) the pterygopalatine fossa was dissected with mobilization of the ICA and resection of the Eustachian tube. The average “angle” and “reach” advantages for CTM were 25.6-degree greater angle of approach behind the petrous ICA and 1.4-cm more lateral reach. Conclusion The techniques and anatomical landmarks for CTM to the PA and PCR are described. Compared with a purely EEA, the CTM provides significant “angle” and “reach” advantages for the PA and PCR.

Tentorial Peeling: Surgical Extradural Navigation to Protect the Temporal Lobe in the Focused Combined Transpetrosal Approach

BACKGROUND Transpetrosal approaches have been used for treatment of tumors in the petroclival region for many years. Injury to the temporal lobe, however, has been a potential drawback of the techniques described to date. OBJECTIVE To describe modifications of the transpetrosal surgical technique, which allows extradural manipulation of the temporal lobe during the focused combined transpetrosal approach. This extra layer of protection avoids mechanical brain retraction, direct trauma to the temporal lobe and disruption of the local venous structures. METHODS The present manuscript describes an innovative technical nuance based on the combination of the focused combined transpetrosal approach, the peeling of the dural layers of the tentorium, and the reverse peeling of the middle fossa dura mater. Ample illustrative material is provided and illustrative cases are presented. CONCLUSION Peeling of the dural layers of the tentorium is a promising modification of the transpetrosal approach to increase the safety of the temporal lobe manipulation.