Anatomical study of presigmoid-retrolabyrinthine approach based on temporal bone high-resolution CT

Anatomical significance of the vestibular aqueduct in posterior wall of the internal auditory canal drilling through the retrosigmoid approach: a study utilizing 3D reconstruction technology

The anatomical importance of the vestibular aqueduct and posterior semicircular canal is explored in this study, which utilizes three-dimensional(3D) image reconstruction and registration fusion technology through the retrosigmoid approach for drilling the posterior wall of the internal auditory canal. A total of 200 temporal bone high-resolution computed tomography (HRCT) scans were collected from 100 patients without inner ear diseases at the Central Hospital of the PLA's Neurosurgery and Radiology Department between 2016 and 2024. Additionally, temporal bone HRCT and brain MRI imaging data were also collected concurrently from 32 patients diagnosed with vestibular schwannomas. The primary focus of this research is on 3D reconstruction and fusion registration of temporal bone HRCT and brain MRI images to accurately display and measure the anatomical structures as well as provide spatial positioning data in 3D dimensions for important structures such as the vestibular aqueduct, posterior semicircular canal, tumors, among others. Several important anatomical measurements were obtained using the 3D Reconstruction and fusion Technology. In non-tumor patients, the internal auditory canal measures (8.408 ± 1.078 mm), with P-1 (defined as the pole located near the posterior region on the long axis of an elliptical opening in the inner auditory canal) to vestibular aqueduct being (9.450 ± 1.522 mm) and to posterior semicircular canal being (10.348 ± 1.542 mm). In vestibular schwannoma patients, these dimensions change to (7.977 ± 0.903) mm, (7.598 ± 1.223 mm), and (8.687 ± 1.061 mm) respectively. Statistical analysis shows significant differences (p = 5.7416e-10 < 0.05, p = 5.8961e-9 < 0.05, p = 6.0e-6 < 0.05). ROC analysis sets a threshold of 8.438 mm from the internal auditory canal to the vestibular aqueduct, warning of caution near 8 mm during surgery to prevent vestibular aqueduct damage. In patients with vestibular schwannoma, the distance from the posterior internal auditory canal to the vestibular aqueduct is shorter compared to that of the posterior semicircular canal, implying a higher likelihood of damaging the vestibular aqueduct when eroding the posterior internal auditory canal during surgery.

Retrolabyrinthine approach to the lateral skull base: The value of preoperative temporal bone CT analysis

PURPOSE

The most used neurosurgical approach to reach cerebellar-pontine angle is the retrosigmoid route. This article describes the presigmoid approach which requires excellent knowledge of the labyrinthine block together with quantitative analysis of temporal bone CT.

METHODS

CT-based quantitative measurements were obtained in patients undergoing vestibular neurectomy with a presigmoid approach. Eighteen patients were enrolled, and five measures were taken: Trautmann's area, the petro-clival angle, presigmoid dura length and its angle. The relationship between these measurements and hospitalization days, operating times, and complications was explored.

RESULTS

The posterior semicircilar canal (PSC)-sigmoid sinus (SS) distance, presigmoid dura- internal auditory canal (IAC)-PSC angle, and duration of surgery are predictors of complications. Specifically, a PSC-sigmoid sinus distance <11 mm, a dura presig-IAC-PSC angle <14 are associated with the highest risk of complications.

CONCLUSION

Preoperative temporal bone CT scan can guide the surgeon through the narrowest areas of the surgical approach. Trautmann's triangle area and petro-clival angle reduction are challenging and can be faced with combined microscopic-endoscopic technique, and with optics angulation-rotation. The retrolabyrinthine approach can enable hearing preservation and minimal cerebellar retraction.

Clinical correlation research of 3D reconstruction of retrolabyrinthine space based on HRCT of temporal bone

Background: The retrolabyrinthine approach helps clinicians perform complex surgeries such as vestibular neurectomy, resection of petrous apex cholesteatoma, or use this space to complete endoscopic combined with microscope surgical operations in a relatively safe buffer space. Some of our current studies using 3D reconstruction in the clinic have also helped us perform some complex surgical procedures.Objective: This study aims to reveal the relationship between important structures in retrolabyrinthine space through objective parameters. These measurement data help clinicians locate intraoperatively and provide a reference for clinical surgery. Also, we are intended to help improve surgical techniques and expand the operating space to increase reachable anatomic structure.Material and Methods: The inner structures of the temporal bone from HRCT (High-resolution computed tomography) images which were taken at the Eye & ENT Hospital of Fudan University were reconstructed. Precise measurement of the structures was accomplished by using the software 3D-Slicer (3D Slicer, https://www.slicer.org/; version 4.8.0, Massachusetts, USA).Results: 3D model of temporal bone structures, including the cochlea, semicircular canals (SCCs), the internal auditory canal (IAC), facial nerve (FN), jugular bulb(JB), and carotid artery was reconstructed. The combination of HRCT and 3D models is utilized to analyze the Quantitative data of the retrolabyrinthine space and its adjacent structures.Conclusions and Significance: 3D reconstruction of CT images clearly displayed the detailed structures of the temporal bone. Surgical adaptability of the retrolabyrinthine approach can be assessed preoperatively by image and other methods, and anatomical parameters play an important role in the retrolabyrinthine space. Therefore, this study helps to skeleton the bone as much as possible to expand the surgical space, so that the surgeon can contact the anatomical structure more diversified to expand the surgical indications.

Feasibility Analysis and Surgical Details of Vestibular Schwannoma Resection via Retrolabyrinthine Approach With Preservation of Endolymphatic Sac

Objectives: To study the feasibility of reserving the endolymphatic sac in the cerebellopontine angle (CPA) and the fundus of the internal auditory canal (IAC) by the retrolabyrinthine approach. Design: Single-center retrospective study. Methods: Through 3-dimensional preoperative computed tomography reconstruction, vestibular schwannoma (VS) resection was performed using a retrolabyrinthine approach with preservation of the endolymphatic sac in selected patients, and hearing and facial nerve functions were followed to assess the feasibility of this operation and the effectiveness of function preservation. Results: VS was completely removed in all cases and the postoperative detectable hearing retention rate (AAO-HNS hearing rating grade A, B, and C) was 80% (4/5). Postoperative facial nerve function was well preserved (HB grade I), no leakage of cerebrospinal fluid or other cranial complications was observed in all patients, and no recurrence was observed during follow-up. Conclusions: With less trauma and a promising route for hearing preservation and facial nerve functions, the retrolabyrinthine approach is a potential choice for the treatment of VS located in the IAC-CPA.

Long-Term Hearing Stability at Different Frequencies after Lower Intact Bridge Tympanomastoidectomy and Possible Theoretical Basis

Objective: We aimed to review the long-term hearing outcomes of intact bridge tympanomastoidectomy (IBM) to discuss hearing preservation and combine the theory of "modified miniature lung," middle ear ventilation, and gas pressure balance theory to explore the possible reasons for long-term stable hearing. Study Design: We designed a collection of patients with chronic suppurative otitis media (CSOM) who underwent IBM and divided them into 2 groups to compare long-term and short-term hearing level. Setting: From April 2007 to July 2017, 102 patients received IBM for CSOM treatment in Eye & ENT Hospital of Fudan University. Methods: We divided the patients into 2 groups according to whether the follow-up period was longer than 6 months. We used the numerical value of the air-bone gap difference as an index to evaluate the degree of hearing recovery. Results: We found that 99/102 (97.1%) of the hearings were improved to more than 3 frequencies. There was no significant difference between long-term hearing level and short-term hearing level, which means IBM could get long-term hearing stability. Conclusion: Intact bridge tympanomastoidectomy could provide significant hearing recovery and long-term hearing stability.