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  • Maximizing the Sub-Temporal Window: Tailored Modular Exposure of Middle Fossa, Posterior Fossa, and Combined Lesions

    Final Number:

    BEATRICE BOIDO MD; Alejandro Mercado Santori MD; Christopher Patrick Carroll MD MA; Norberto O. Andaluz MD; Ravi MD Samy; Paolo Cappabianca MD; Mario Zuccarello MD

    Study Design:
    Laboratory Investigation

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2017 Annual Meeting

    Introduction: The optimal surgical approach to complex petroclival lesions is strongly debated. These lesions are deep, intimately associated with critical neurovascular structures, and demand surgical approaches tailored to lesion’s unique anatomic relationships to minimize surgical morbidity. We evaluated the volume of bony removal required for and surgical working area developed by modular transpetrous expansion of the standard sub-temporal window.

    Methods: Cadaveric heads (N=5) were fixed in formaldehyde prior to undergoing high resolution computed tomography (CT) scan. A sub-temporal craniotomy was performed followed by sequential, modular transpetrous extensions [anterior petrosectomy; partial-posterior petrosectomy; internal acoustic canal (IAC) exposure; and translabyrinthine extension]. A high-resolution CT scan was obtained after each modular expansion; overlapped to the preoperative CT; and bone removal volume was calculated. BrainLab image-guidance was used to measure the working area created by each modular expansion.

    Results: A Kawase approach was performed without opening the IAC, requiring mean bony removal of 1.3cm3 to produce a mean working area of 24.2mm2. Unroofing the IAC required mean bony removal of 0.3cm3 [0.2-0.4cm3] and yielded an increased working area of 32.8mm2. Next, a modified posterior petrosectomy was performed (drilling of Trautmann’s Triangle) with mean bony removal of 4.3cm3; the working area increased to 67.0mm2. Finally, a translabyrinthine extension was performed requiring mean bony removal of 7.1cm3 to create a final working area of 81.7cm2. Each modular transpetrous extension of the sub-temporal window resulted in statistically significant increases in surgical working area (p<0.05).

    Conclusions: Each modular expansion of the sub-temporal craniotomy window resulted in progressively increased surgical working area (p<0.05). The combination of an anterior and partial-posterior petrosectomy provided the greatest increases in middle and posterior fossa exposure. By utilizing modular transpetrous extensions, skull-base surgeons can maximize the sub-temporal window to tailor exposure of petroclival lesions of the lateral skull base from CN-III to CN-IX while preserving hearing.

    Patient Care: Our cadaveric study demonstrates the feasibility of addressing a variety of complex petroclival regions via modular expansions of the familiar extradural sub-temporal approach. This can be performed to access lesions from the level of the oculomotor nerve superiorly to the glossopharyngeal and vagal nerves inferiorly with preservation of hearing.

    Learning Objectives: By the conclusion of this session, participants should be able to: (1) Describe principles and pertinent operative anatomy of the sub-temporal window and its transpetrous modular extensions. (2) Discuss, in small groups, how the different modular extensions of the sub-temporal window can be used to expand the surgical exposure to lateral skull base lesions from the petroclival junction to the cerebellopontine angle. (3) Identify an effective modular expansion of the sub-temporal window to effectively address sample case presentations.

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