A Modular Approach for Accessing Skull Base Pathology Using Subcortical White Matter Tracts as a Framework: The Ventral Anteromedial Approach

Background Selecting a favorable corridor is a critical consideration in skull base surgery, and relies heavily upon the location of neurovascular structures. The role of DTI-based white matter tractography in improving surgical planning and clinical outcomes in resection of intra-axial lesions has been recently established. However, its applicability in corridor-based skull base surgery has not yet been evaluated. In this report we establish a radial framework for ventral anteromedial approach, consisting of osseous, soft-tissue, vascular and neural frameworks, while using DTI as the primary imaging modality.

Methods Five formalin-fixed cadavers were studied using five endoscopic endonasal approaches (EEAs) to identify surgical landmarks and anatomical barriers of the median ventral skull base. 3D imaging and correlative CT-guided navigation using novel planning software (Bright Matter Vision, Toronto, Canada) was performed, paying particular attention to the orthogonal plane of each approach. Clinical cases showing each EEA corridor are shown.

Results Cadaveric dissections allowed us to construct a radial framework for the anteromedial corridor to the ventral median skull base plane, as follows:

Approach: EEA (transcribriform, transplanum, transsellar, transclival).

1. Outer radial corridor:

a. Osseous envelope: frontal base, sphenoid, sella, clivus.

b. Soft tissue envelope: nasal space, frontal, ethmoid, sphenoid sinuses.

2. Inner radial corridor:

a. CN: II, V2, VI

b. White matter tracts: UF, Cingulum, IFOF, olfactory tracts.

c. Vessel: internal carotid artery segments (intradural, paraclinoid, parasellar, paraclival).

Conclusion The ventral anteromedial corridor is critically bounded by the relative position of the optic nerve and superior orbital fissure that represent the relative lateral boundaries. These structures are visible and demonstrable in a 3D rendering software platform using multimodality imaging. The presented module presents the radial architecture of the ventral anteromedial corridor.