J Neurol Surg B Skull Base 2017; 78(S 01): S1-S156
DOI: 10.1055/s-0037-1600531
Oral Presentations
Georg Thieme Verlag KG Stuttgart · New York

The Ventral Perspective: Topographic Neurovascular Anatomy of the Cranial Base From an Endoscopic Endonasal Perspective: The Paramedian Region

Lior Gonen
1   Aurora Neuroscience Innovation Institute, Milwaukee, Wisconsin, United States
,
Srikant S. Chakravarthi
1   Aurora Neuroscience Innovation Institute, Milwaukee, Wisconsin, United States
,
Martin Corsten
1   Aurora Neuroscience Innovation Institute, Milwaukee, Wisconsin, United States
,
Amin B. Kassam
1   Aurora Neuroscience Innovation Institute, Milwaukee, Wisconsin, United States
› Author Affiliations
Further Information

Publication History

Publication Date:
02 March 2017 (online)

 

Introduction: There are two primary considerations in accessing targets within the central skull base:

1. The 360‐degree circumferential corridor (CC): anterior medial/lateral, lateral, and posterior lateral) (previously described) and

2. The Radial Corridor (RC): Outer‐Radial Corridor (ORC): osseous and soft‐tissue envelopes; Inner‐Radial (IRC): Neural (cranial nerves and parenchyma) and Vascular.

Endoscopic endonasal approaches (EEA) represent an anteromedial CC to the ventral cranial base, viable alternatives to conventional transfacial/transoral ORCs, thereby important to the armamentarium of contemporary skull base surgery. In this report we present a 3D model of the osseous, vascular (internal carotid [ICA]) and correlative cranial nerve (CN) framework. We add in relevant CN and soft‐tissue envelopes from the ventral perspective. For the paramedian plane, we focus on IRCs lateral to respective ICA segments and respective ORCs (transmaxillary corridor, pterygopalatine fossa, and lateral parapharyngeal space).

Methods: EEA dissections were performed in five cadaveric specimens. Topography of the neurovascular structures within the osseous framework of the cranial base was recorded in 3D and correlated with orthogonal and radially‐stacked views using a 3D rendering software (Synaptive Medical, Toronto, ON) with multimodality imaging. These 3D rendered views were then combined with EEA views using a template of ICA coursing through the respective osseous framework to create a anatomic background palate. On this platform, position of CN nerves were superimposed by individually dissecting them and correlating them with 3D rendering. Finally, a soft‐tissue envelope of relevant muscles were layered on top of the IRC to provide a comprehensive ventral perspective of EEA paramedian corridor selected. Each of the respective modules were assessed for viability based on preoperative 3D planning and ability to actually execute against this plan with a variety of pathology.

Results: Based on the ICA and relevant cranial nerves the IRCs for EEA to the paramedian ventral cranial base may be described as 2 distinct modules: (1) Zone IV – Inferior paramedian zone, extends from the medial pterygoid plate medially to the subtemporal fossa laterally, confined superiorly by the middle fossa floor (contains parapharyngeal and petrous ICA segments, medial: vidian nerve and canal, lateral: V3 and superomedial: V2 division of CN V as they enter into the infratemporal fossa; (2) Zone V – Superior paramedian zone, oblique line joining the Foramen rotundum and vidian inferior‐medially to the sagittal plane of the foramen ovale posterior‐laterally; includes the lateral recess of the sphenoid sinus and is confined inferiorly by the middle fossa floor (contains the paraclival and parasellar CA segments, CN III, IV and VI in the cavernous sinus, SOF, V1‐V3.

Conclusion: The paramedian ventral cranial base is directly accessible via anteromedial circumferential endonasal corridor. The proposed classification divides the paramedian region into 2 modules based on the correlative inner radial corridor bound by the position of the respective cranial nerves and the relationship with the ICA. This has proven to translate operatively independent of pathology subtypes. Therefore, this classification provides a practical algorithmic guide that further refines our previously described approaches to median cranial base lesions, respecting the plane of the cranial nerves as the defining anatomic determinant of the IRC.