Redefining the Surgical Approaches to the Anterior Cranial Base: The Anterior Radial Corridor

Introduction: Many surgical approaches to the anterior skull base have been described; however, its evolution has led to confusing nomenclature and there is little consensus on their indications. In this review, we aim to describe a simple and clear methodology for classifying the anterior radial corridor at the cranial base. We here introduce the term “vector” to better organize our revised surgical corridors.

Objective: To organize access to the anterior skull base using a novel circumferential-radial coordinate 3-vector system in selecting the most appropriate surgical corridor.

Methods: A detailed literature search using MEDLINE and SCOPUS databases was performed, using nomenclature of both dorsal and ventral conventional skull base approaches as keywords. Cadaveric dissections were performed to show the relevant anatomic landmarks of the anterior corridor. Three vectors were defined: (1) Vector 1—corresponds to a dorsal or ventral corridor depending on the relative position of the lesion in relation to the cranial nerves. (2) Vector 2—created by outer and inner circumferences; the outer circumference (OC) is formed by the osseous and soft tissue anatomy and the inner circumference (IC) contains the neurovascular elements; (3) Vector 3—corresponds to the Radius (target), which is a key determinant in deciding selection of the appropriate radial corridor. The radius is defined by the Neural Network and vascular elements. Based on these principles, a decision-making algorithm will be presented.

Result: Cadaveric dissections revealed the following anatomical landmarks: (1) Dorsal anterior corridor: The OC extends from the orbital notch and the nasion, to the contralateral orbital notch; this region contains the frontalis muscle and glabella. The IC is formed by the orbital gyri, olfactory cistern, optic chiasm and sellar and suprasellar regions; the Radius is the dorsal chiasm. (2) Ventral anterior corridor (extends from optic nerve to optic nerve): The OC is formed by the frontal sinus, anterior ethmoidal canal, frontoethmoidal suture, cribriform plate, posterior ethmoidal canal, planum, limbus, tuberculum sellae. The medial plane represents the perpendicular plate, and superior and middle turbinate. The IC contains elements of the olfactory, interhemispheric cistern, and chiasmatic cistern. The radius represents the ventral olfactory tract and chiasm. Two clinical cases were reviewed to assess the impact of multimodal imaging and correlate it with anatomy in selecting and executing the appropriate corridor.

Conclusion: We here introduce a novel radial-coordinate system in an effort to reduce the noise-to-signal ratio of surgical approaches to the anterior skull base. A decision-making algorithm has been created to better organize access to this region. Each dorsal and ventral radial corridor has a precise indication according to the position of the pathology relative to the neurovascular elements.

No conflict of interest has been declared by the author(s).