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Image-guided, microsurgical topographic anatomy of the endolymphatic sac and vestibular aqueduct via a suboccipital retrosigmoid approach

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Abstract

The endolymphatic sac (ES) and the vestibular aqueduct (VA) are often in the surgical field when posterior fossa lesions are targeted using retrosigmoid approaches. The purpose of this work is to validate neuronavigator accuracy in predicting VA location as well as to give guidelines to preserve the ES and VA. A retrosigmoid approach was performed bilaterally in six specimens in the semisitting position. Preoperatively, we registered in the CT scans the position of the VA genu (virtual genu). After the approach execution, ES and VA genu topographic relationships with evident posterolateral cranial base structures were measured using neuronavigation. Next, we exposed the VA genu: its position coincided with the virtual VA genu in all the specimens. On the average, the ES was 17.93 mm posterosuperolateral to the XI nerve in the jugular foramen, 12.26 mm posterolateral to the internal acoustic meatus, 20.13 mm anteromedial to the petro-sigmoid intersection at a point 13.30 mm inferior to the petrous ridge. The VA genu was located 7.23 mm posterolateral to the internal acoustic meatus, 18.11 mm superolateral to the XI nerve in the jugular foramen, 10.27 mm inferior to the petrous ridge, and 6.28 mm anterolateral to the endolymphatic ledge at a depth of 3.46 mm from the posterior pyramidal wall. Our study demonstrates that is possible to use neuronavigation to reliably predict the location of the VA genu. In addition, neuronavigation may be effectively used to create a topographical framework that may help maintaining the integrity of the ES/VA during retrosigmoid approaches.

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Conflict of interest

The authors report no conflict of interest.

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Authors and Affiliations

  1. Dardinger Microneurosurgical Skull Base Laboratory, Department of Neurological Surgery, Wexner Medical Center, The Ohio State University, N1025 Doan Hall, 410 West 10th Avenue, Columbus, OH, 43210, USA

    Roberto Colasanti, Al-Rahim Abbasali Tailor & Mario Ammirati

  2. Department of Neurosurgery, Umberto I General Hospital, Università Politecnica delle Marche, Ancona, Italy

    Roberto Colasanti

  3. Department of Radiology and Wright Center of Innovation in Biomedical Imaging, Wexner Medical Center, The Ohio State University, Columbus, OH, USA

    Jun Zhang

Authors
  1. Roberto Colasanti
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  2. Al-Rahim Abbasali Tailor
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  3. Jun Zhang
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  4. Mario Ammirati
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Correspondence to Mario Ammirati.

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Comments

Nicholas C. Bambakidis, Cleveland, USA

This is an anatomic paper investigating the usefulness of neuronavigation in aiding identification of and preservation of the endolymphatic sac (ES) and vestibular aquaduct (VA). The authors have produced a nice set of data from their cadaveric dissections; as with all such papers, the actual utility of the data is dubious. Nevertheless, we have found that careful study of the anatomic relationships between these landmarks can be of use in many surgical procedures around the internal auditory canal and cerebellopontine angle.

Atul Goel, Mumbai, India

The endolymphatic sac and duct are important structures that innocuously occupy a position in the petrous bone limited anteriorly by the 7th to 11th nerve complexes, superiorly by the petrous ridge and posteriorly and inferiorly by the sigmoid sinus. Though the retrosigmoid suboccipital approach is a very commonly used approach, the anatomy and preservation of the endolymphatic sac and duct is not a common subject of discussion. The authors have elaborately discussed the anatomy of the endolymphatic system and have elegantly showed the use of neuronavigation to identify and preserve these structures.

The significance of endolymphatic sac and vestibular aqueduct is unclear even to an otolaryngologist. The exact role this anatomical structure plays in hearing and in ‘vertigo’ is more of speculation and individual conjectures. Translabyrinthine approaches will certainly sacrifice the ES and VA. Retrosigmoid operations have the advantage that endolymphatic sac and VA can be preserved. Currently, my surgical strategy in vestibular schwannomas is to avoid drilling of the internal acoustic meatus in most cases. In general, drilling of the internal acoustic meatus should be minimized to 5–6 mm posterolaterally. This avoids injury to the vestibular apparatus, the endolymphatic structures, and a high-riding jugular bulb and avoids opening of the air cells.

Ammirati et al. present a cadaveric study and show the advantages of using navigation system to identify the structure and preserve it. Although technological assistance is always welcome, the well-defined anatomic landmarks and parameters that are the basis of all temporal bone surgery can be foolproof. Essentially, while technology is helpful, the importance of anatomical understanding cannot be ignored.

Despite this, the endolymphatic sac is a well-defined anatomical entity and should be preserved wherever and whenever possible.

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Colasanti, R., Tailor, AR.A., Zhang, J. et al. Image-guided, microsurgical topographic anatomy of the endolymphatic sac and vestibular aqueduct via a suboccipital retrosigmoid approach. Neurosurg Rev 38, 715–721 (2015). https://doi.org/10.1007/s10143-015-0634-2

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  • DOI: https://doi.org/10.1007/s10143-015-0634-2

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