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  • The Infralabyrinthine Route to the Petrous Apex: A Comparison of the Extradural Infralabyrinthine and Retrosigmoid Intradural Inframeatal Approaches

    Final Number:

    Marcus Acioly MD; Alexander I Evins MD; Philip E. Stieg MD, PhD; Antonio Bernardo MD

    Study Design:
    Laboratory Investigation

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2016 Annual Meeting

    Introduction: The extradural infralabyrinthine approach (ILA) is often preferred in patients with lesions of the petrous apex and serviceable hearing. Recently, the retrosigmoid intradural inframeatal approach (RIIA) was described as a viable alternative with successful results. Since the ILA and the RIIA share the same surgical corridor, we compare both techniques anatomically.

    Methods: Three adult cadaveric heads (6 sides) injected with colored latex underwent RIIA and ILA approaches to study the neurovascular structures and surgical landmarks. Dimension of the access window, area of exposure, angle of view, and depth of field were measured and analyzed.

    Results: The average vertical dimensions and areas of exposure for the ILA and RIIA were 6.56 mm and 7.07 mm, and 63.77 mm2 and 51.95 mm2, respectively. The horizontal dimensions were similar in both approaches. After detachment and slight retraction of the jugular bulb, the vertical dimensions of the ILA further increased to 10.86 mm (range: 7.49–14.23 mm) and the area of exposure increased to 86.40 mm2 (range: 58.81–114 mm2). The depth of the surgical field at the petrous apex in the RIIA (mean: 48 mm) was deeper than that of the ILA (mean: 41.7 mm) and the angle of view was directed toward the internal carotid artery.

    Conclusions: The extradural ILA provides a larger area of exposure compared to the RIIA in normal anatomical specimens. The ILA to the petrous apex is a time-consuming and technically demanding approach but the RIIA requires cerebellar retraction and places the endolymphatic sac at risk of injury.

    Patient Care: By helping surgeons select the most optimal approach for a given lesion in this region.

    Learning Objectives: By the conclusion of this session, participants should be able to understand the differences between the extradural infralabyrinthine approach and the retrosigmoid intradural inframeatal approach.


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