Endolymphatic Duct Violation During Retrosigmoid Dissection of the Internal Auditory Canal: A Human Temporal Bone Radiographic Study

Operational Analysis of Trautman's Triangle in Petroclival Region Approaches: Cone-Beam Computed Tomography Study

OBJECTIVE

This study was conducted to evaluate the anatomical and clinical features of Trautman's triangle (TT) and to better understand the possible surgical corridor for other surgical approaches involving the petroclival region, especially the presigmoid retrolabyrinthine approach.

METHODS

In this study, morphological analysis of structures related to TT was performed from cone beam computed tomography images of 134 female and 206 male individuals aged 18-65 years.

RESULTS

The TT area was observed as 5.6% (n = 19) type I, 63.2% (n = 215) type II, and 31.2% (n = 106) type III. It was determined that 87.6% of the sigmoid sinus (SS) was lateral to the posterior semicircular canal and 12.4% was medial. It was determined that the TT area showed a positive correlation with petrous slope and a negative correlation with mastoid aeration. In other words, as the TT area increased, the petrous inclination angle also increased, but the mastoid aeration decreased. It was also found that the TT area was associated with the location of the SS and the largest TT area (164.84 ± 42.29 mm2) was observed in the posteriorly located SS.

CONCLUSIONS

The relationship between TT and SS, petroclival angle, mastoid aeration, and subarcuate fossa has a very dynamic structure. Understanding the variations and clinical significance of these structures in the petroclival region is critical in determining the surgical approaches to be applied and understanding the etiology of vestibular system diseases.

Arachnoid and dural reflections

The dura mater is the major gateway for accessing most extra-axial lesions and all intra-axial lesions of the central nervous system. It provides a protective barrier against external trauma, infections, and the spread of malignant cells. Knowledge of the anatomical details of dural reflections around various corners of the skull bases provides the neurosurgeon with confidence during transdural approaches. Such knowledge is indispensable for protection of neurovascular structures in the vicinity of these dural reflections. The same concept is applicable to arachnoid folds and reflections during intradural excursions to expose intra- and extra-axial lesions of the brain. Without a detailed understanding of arachnoid membranes and cisterns, the neurosurgeon cannot confidently navigate the deep corridors of the skull base while safely protecting neurovascular structures. This chapter covers the surgical anatomy of dural and arachnoid reflections applicable to microneurosurgical approaches to various regions of the skull base.

Usefulness of the radiological planning for hearing preservation surgery in vestibular schwannoma

Purpose

During vestibular schwannoma surgery there is a risk of endolymphatic duct and sac injury, which may cause a loss or a deterioration of hearing. The goal of the study was to evaluate the empirical utility of presurgical planning using CT with the bone window for the hearing preservation surgery.

Methods

The study was performed on 14 human temporal bones. CT scans with the bone window were obtained in the standard position. Safe drilling line was evaluated and after that drilling distances were analysed: the lateral drilling distance, total length of internal acoustic meatus, drilled length of internal acoustic meatus. After this, a surgical exposure was performed, using size of a drill tip as measuring scale. The dura was excised and endolymphatic duct was injected with a latex. Revision of the internal acoustic meatus was performed with the use of a microscope.

Results

Mean results of safe drilling coefficients were: lateral drilling distance: 10 ± 2 mm, total length of internal acoustic meatus: 9 ± 2 mm, drilled length of internal acoustic meatus: 7 ± 2 mm. In all cases, no endolymphatic duct injury was observed.

Conclusions

Preoperative radiological planning using the safe drilling coefficients is of value for the hearing preservation surgery in vestibular schwannoma. The size of the drilling tip may be used as an intraoperative measuring scale during this procedure. However, CT with a bone window is a necessary tool for the purposes of this procedure.

Surgical exposure of the internal auditory canal through the retrosigmoid approach with semicircular canals anatomical preservation

OBJECTIVE

Evaluate the feasibility of an adequate exposure with anatomical preservation of labyrinth structures through retrosigmoid transmeatal approach (RSA) in surgeries for resection of acoustic neuromas/vestibular schwannomas (VS).

METHOD

Thirty patients underwent surgical resection and were preoperatively evaluated with fine slice high definition CT scans and 3D-MRI volumetric reconstructions. Extension of internal auditory canal (IAC) opening during surgery was measured using 3 mm right-angle calibrated hook and neuronavigation parameters. Postoperatively, the extension of IAC opening and integrity of the labyrinth were confirmed through preoperatively images procedures.

RESULTS

The preoperative length of IACs varied between 7.8 and 12.0 mm (mean 9.3 mm, SD 0.98, 95%CI 8.9 to 9.6, and median 9.0 mm). Postoperative images demonstrated adequate opening of the IAC and semicircular channels integrity.

CONCLUSION

A complete drilling of the posterior wall of IAC through the RSA is feasible and allows direct visualization of the IAC-fundus without damaging the semicircular canals.

Endolymphatic duct blockage: a randomized controlled trial of a novel surgical technique for Ménière's disease treatment

OBJECTIVES

To compare the effectiveness of the endolymphatic duct blockage (EDB) and the endolymphatic sac decompression (ESD) to control Ménière's disease symptoms and to evaluate their effect on hearing level.

STUDY DESIGN

Prospective nonblinded randomized study.

SETTING

Tertiary medical center.

SUBJECTS AND METHODS

Fifty-seven patients affected by a refractory Ménière's disease were included out of which 22 underwent an ESD and 35 underwent an EDB. Five periods of follow-up were considered: 0 to 1 week, 1 week to 6 months, 6 to 12 months, 12 to 18 months, and 18 to 24 months. Mean outcome measurements consisted of vertigo control, tinnitus, aural fullness, instability, and hearing level. Hearing level was evaluated using pure-tone average (PTA) and speech discrimination score (SDS).

RESULTS

There was no significant difference between the 2 groups in the number of vertigo spells per months preoperatively (P = .153). Twenty-four months postoperatively, 96.5% of the EDB group had achieved a complete control of vertigo spells against 37.5% of the ESD group with a statistically significant difference (P = .002). There was a better control of tinnitus and aural fullness with EDB (P = .021 and P = .014, respectively). There was no statistically significant difference in hearing level preoperatively (P = .976) and 24 months postoperatively (P = .287) between the 2 groups. Hearing level was preserved in each group with no significant difference between the preoperative and the postoperative levels (P > .05).

CONCLUSION

EDB is more effective than the traditional ESD in controlling the symptoms of Ménière's disease. It is a novel surgical technique with promising results for a complete treatment of Ménière's disease. There are no significant complications or adverse effect.

Topographic Changes in Petrous Bone Anatomy in the Presence of a Vestibular Schwannoma and Implications for the Retrosigmoid Transmeatal Approach

BACKGROUND:

The maneuver of transmeatal drilling carries the risk of injuring inner ear structures, which may cause immediate or delayed hearing loss.

OBJECTIVE:

To describe the changes in petrous bone anatomy caused by the tumor and to analyze both the incidence and the risk pattern for violation of the endolymphatic system in a surgical series.

METHODS:

One hundred patients operated on for vestibular schwannoma were included in this prospective study. Thin-slice computed tomography was performed before and after surgery. We assessed topographic measurements on both the pathological and healthy sides. Postoperatively, we evaluated anatomic and functional values.

RESULTS:

The diameter of the internal auditory canal was significantly larger (P < .001) in the petrous bones of the affected sides than in the contralateral healthy sides. An average of 5.6 ± 1.8 mm of the internal auditory canal was drilled, and the distance from the medial border of the sigmoid sinus to the drilling line (tangential to the drilled surface of the posterior lip of the internal auditory canal) was 9.8 ± 2.9 mm. A postoperative violation of the vestibular aqueduct (VA) was detected in 41 cases; the VA was intact in 55 cases; and the VA could not be clearly defined in 4 cases. The incidence of VA injury increased with increasing tumor size. In the patient group with good preoperative and postoperative hearing function, a VA injury occurred in 26% of cases, whereas the incidence increased to 67% in preoperatively deaf patients.

CONCLUSION:

Vestibular schwannomas cause significant distortion of the petrous bone anatomy. Detailed preoperative knowledge of the topography is necessary for the preservation of function.

Controversies in building a management algorithm for vestibular schwannomas

PURPOSE OF REVIEW

The present review examines the various mainstream treatment options, benefits and risks, and controversies involved in developing a management algorithm for treatment of vestibular schwannoma.

RECENT FINDINGS

Advances in microsurgery and radiosurgery have made tremendous contributions to management of vestibular schwannoma; however, considerable controversy still exists. The auditory and facial nerve functional outcomes have improved with use of intraoperative monitoring for vestibular schwannoma removal and with lower radiosurgery doses; however, risks to the facial and auditory nerves still exist. Observing vestibular schwannomas for growth with serial magnetic resonance imaging is an increasingly popular option for small vestibular schwannomas that allows patients to enjoy hearing and facial function.

SUMMARY

The risks and benefits of each treatment option must be weighed for each patient, and management decisions regarding vestibular schwannomas should be individualized for each patient depending on tumor anatomy, patient preferences, and symptoms.

Endolymphatic Duct Status During Middle Fossa Dissection of the Internal Auditory Canal: A Human Temporal Bone Radiographic Study

OBJECTIVE

Successful hearing preservation after acoustic neuroma resection is sometimes complicated by delayed hearing deterioration. The middle fossa approach appears to offer superior long-term hearing results when compared to the retrosigmoid surgical approach. The goal of this study is to investigate the hypothesis that internal auditory canal (IAC) drilling during middle fossa acoustic neuroma removal is associated with a lower incidence of endolymphatic duct (ELD) injury, a potential cause of delayed hearing loss (HL) known to accompany retrosigmoid hearing preservation dissection techniques.

STUDY DESIGN

A human temporal bone anatomic and radiographic study complemented with a literature review.

METHODS

Twenty human temporal bones were analyzed with high-resolution multislice computed tomography (HRMCT) and subjected to standard extended middle fossa IAC dissection with labyrinthine preservation and follow-up HRMCT for analyses of the ELD.

RESULTS

Zero of 20 (0%) temporal bones were found to have violation of the ELD with preservation of the labyrinthine structures and the endolymphatic sac. Reviews of human and animal studies indicate that injury to the ELD may create endolymphatic hydrops, a known cause of hearing deterioration.

CONCLUSION

The ELD is not vulnerable to injury during IAC dissection using the middle fossa approach. A previous radiographic study has shown that the ELD is violated in 24% of temporal bones during retrosigmoid dissection of the IAC. These findings support and may help explain other outcome studies that show that long-term hearing results are superior with the use of the middle fossa approach when compared to results following retrosigmoid dissection.