Effect of Sigmoid Sinus Position on the Difficulty and Approaches to Cochlear Implantation Surgery

Evaluation of the Sigmoid Sinus Morphology by Cone Beam Computed Tomography; Touchstone of the Posterior Cranial Fossa

OBJECTIVE

In this study, we aimed to analyze the relationship of the sigmoid sinus (SS) with the external auditory canal, facial nerve, and mastoid cells from an anatomic point of view, to define the position of the SS during transmastoid, translabyrinthine, retrosigmoid (lateral suboccipital) approaches, in tympanomastoidectomy and posterior cranial fossa surgery.

METHODS

In this study, the morphologic structures associated with the sigmoid sinus were evaluated in cone beam computed tomography images taken between 2015 and 2022. The images of 68 men and 106 women, aged 18-65 years, obtained from the archive of Ankara University Faculty of Dentistry, Department of Oral and Maxillofacial Radiology were analyzed.

RESULTS

The most common SS pattern was type II, with a rate of 60.8% (n = 209); the second was type III, with 20.6% (n = 71); and the least common was type I, with 18.6% (n = 64). Although the distance between the horizontal line passing through the external auditory canal and facial nerve and the anterior contour of the SS was highest in type I (right, 7.26 ± 1.62; left, 7.44 ± 0.97), it was lowest in type III (right, 4.40 ± 1.50; left, 4.84 ± 1.16) (P < 0.05).

CONCLUSIONS

This study highlights the importance of the SS position in surgery, with special reference to otologic, neurotologic, and posterior cranial fossa surgery. To avoid intraoperative complications, each patient should be evaluated preoperatively by appropriate radiologic methods.

An inter-observer assessment of mastoid pneumatization and degree classification using sigmoid sinus: comparing two levels of temporal bone computed tomograms

BACKGROUND

The degree of mastoid pneumatization of the temporal bone (TB) has been implicated in the pathogenesis of TB diseases and surgical implications, and planning of a few otologic surgeries. However, there is lack of consensus in the classification of the degree of pneumatization. This study aimed to suggest a simple, quick, and less-burden classification system for assessing and rating the degree of pneumatization by comparing two levels of TB computed tomographs (CTs) using the SS as a reference in an inter-observer assessment among otologists.

METHODS

This was a randomized pilot survey among otologists. A questionnaire consisting of different axial CTs of TB taken at two levels: the level of malleoincudal junction (MIJ) and the level of lateral semicircular canal (LSCC), with different pneumatization patterns, was used to assess participants' impressions of the degree of pneumatization. The terms "hypo-," "moderate," "good," and "hyper-" pneumatization were listed as options to rate their impressions on the degree of mastoid pneumatization of the TB images using the SS as a reference structure. Likert scale was used to assess their level of agreement or disagreement with using SS as a reference in evaluating mastoid pneumatization.

RESULTS

Participants who correctly rated images taken at the level of LSCC according to their respective degree of pneumatization were significantly higher (p < 0.05) regardless of their year of experience compared to those that correctly rated corresponding images taken at the level of MIJ. A 76% positivity in their level of agreement with the use of sigmoid sinus in evaluating mastoid pneumatization was observed on the Likert-scale chart.

CONCLUSION

Findings from this study suggest that evaluating air cells around the SS at the level of LSCC on CTs could be easier in assessing and classifying the degree of mastoid pneumatization.

Bilateral Anterior Displaced Sigmoid Sinus in Cochlear Implantation: A Proposed Solution

To assess the safety, time consumption and presumed postoperative complications of posterior repositioning in cases with bilateral anterior displaced sigmoid sinus (ADSS) having cochlear implant surgery. Cases with bilateral ADSS were included. A cortical bone chip was harvested. Sinus plate was drilled thin and removed, ADSS was repositioned posteriorly and secured by the bone chips. The procedure was completed using the standard posterior tympanotomy (PT) technique. Follow up was done both clinically and by computed tomography (CT). Out of 632 cases operated upon in more than 7 years, only 7 cases had Bilateral ADSS (1.1%) of which 5 were females (71.45%). The average age was 8.2 ± 12 (6 children and an adult). No intraoperative bleeding was encountered in any of the 7 cases. The average operative time was 103.6 ± 9.7 min. No minor nor major complications were detected in all 7 cases. To keep the advantages of PT, repositioning of ADSS in bilateral cases can be done safely with a reasonable increase in the average operative time.

Phenotypical variability of the sigmoid sinus in translabyrinthine and retrosigmoid surgeries

Introduction

We hypothesized that the cranial phenotype influences the shape of the posterior cranial fossa and the relative position of the sigmoid sinus.

Materials and methods

The topography of the sigmoid sinus was studied on 26 magnetic resonance venograms and 35 embalmed cadavers by morphometric analysis, dissection, and photo modeling techniques.

Results

The data show that the transverse diameter of the posterior cranial fossa correlates positively with the laterolateral diameter of the skull. The majority of cases with the low-anterior position of the sigmoid sinus were recorded in the brachycephalic group (82%), while the high-posterior localization of the sigmoid sinus was typical for the dolichocephalic patients (63%). The results of the ANOVA test confirm the significance of differences.

Conclusions

The shape of the skull reflects the morphology of the posterior cranial fossa and influences the topographic characteristics of the sigmoid sinus that must be considered in the selection of surgical approach to the inner ear and pontocerebellar angle.