360º To the Petrous Apex: Comprehensive Surgical Anatomy and Limitations of Open and Endoscopic Endonasal Approaches to the Petrous Apex

Introduction: The contemporary skull base surgeon must understand both transcranial and expanded endonasal approaches (EEAs) to the petrous apex. We provide a comprehensive anatomical overview and comparison of the main approaches to the petrous apex through illustrative anatomical dissections.

Methods: Transcranial approaches were performed under microscopic magnification and EEAs were performed using 0-degree, 30-degree, and 45-degree endoscopes. Dissections were performed until maximal surgical exposure was obtained. 3D macroscopic and endoscopic images were taken for each key step. Each approach was performed on eight sides of four specimens.

Results: The transcranial approaches performed were the anterior petrosectomy with transcavernous extension, the transcochlear approach with mobilization of the facial nerve, and the retrosigmoid approach with suprameatal extension. Endoscopic approaches performed were the transclival-transcavernous approach, the transmaxillary-transpterygoid approach, and the contralateral transmaxillary approach. From the retrosigmoid perspective, the posterior surface of the petrous apex is identified, and its boundaries are the superior petrosal sinus (SPS) superiorly, the sagittal plane of CN VI medially, and the axial and sagittal plane of the porus of the internal auditory canal (IAC) inferiorly and laterally, respectively. Its main advantage is the panoramic exposure that it affords to the posterior fossa and the access it affords to Meckel’s cave once the petrous apex is drilled. The transcochlear approach affords a lateral view of the petrous apex that is bounded medially and inferiorly by the inferior petrosal sinus (IPS), posteriorly by the posterior fossa dura, anteriorly by the petrous portion of the internal carotid artery (ICA), and superiorly by the SPS. The anterior surface of the petrous apex is reached either through the subtemporal or pretemporal route. The boundaries of the petrous apex from the classic subtemporal approach are the petrous ridge posteriorly, the projection of the IAC laterally, the greater superficial petrosal nerve anteriorly, and the lateral boundary of V3 medially. With the pretemporal/transcavernous extension, the main advantage is identifying the medial-most portion of the petrous apex in Parkinson’s triangle (between CN IV superiorly and V1 inferiorly). Benefits of the anterolateral approaches are the wide exposure of the middle fossa and cavernous sinus, and exposure of the posterior fossa once the petrous apex is removed. The EEAs approach the petrous apex from an anteroinferior perspective. The petrous apex from the transclival-transcavernous approach is demarcated by a triangle that consists of CN VI posteromedially, the cavernous ICA anterolaterally, and the pterygosphenoidal fissure inferiorly. To extend exposure of the transclival-transcavernous approach lateral to the cavernous ICA, the contralateral transmaxillary approach can be added. The transmaxillary-transpterygoid approach affords access to the petrous apex in a window between the Gasserian ganglion laterally and the cavernous ICA medially. The benefits of the transclival-transcavernous and the transmaxillary-transpterygoid are the exposure they afford to the posterior and middle fossae, respectively ([Figs. 1]–[3]).

Conclusion: Through anatomical dissections, we describe the different exposures of the petrous apex and related structures as afforded through open approaches and EEAs.

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Artikel online veröffentlicht:
05. Februar 2024