Olfactory Grove Meningiomas: Endoscopic Endonasal Corridors Based on Anatomical Landmarks for Olfaction Revised

Background: Olfactory Groove meningiomas (OGMs) originate at the cribriform plate and the frontosphenoidal suture region, and represents 10% of all intracranial meningiomas. They tend to grow to a large size; often extending from the crista Galli anteriorly to the tuberculum sellae posteriorly. A significant proportion of these patients have impaired olfaction. The olfactory function can decline after surgery; hence, the quality of life (QOL) is affected. Based on previously studied relationship between the ethmoidal arteries (EAs) and the olfactory mucosa, disruption of these arteries during the surgery, and destruction of the fimbria while creating the surgical corridor, can have a negative impact on olfaction.

Objective: To divide the anterior cranial fossa floor into surgical corridors, from an endoscopic endonasal perspective, and to mitigate against loss of olfaction. We propose dividing the anterior skull base into five surgical corridors based on the ethmoidal arteries and the midline.

Materials and Methods: In 20 fresh latex-injected cadaver heads, we exposed the anterior cranial fossa via an endoscopic endonasal approach (EEA). The mucosa of the roof of the nasal cavity medially was dissected, an anterior and posterior ethmoidectomies were performed, the crista Galli and cribriform plate were removed, and the medial wall of the orbit was exposed to identify the anterior and posterior EAs. Draf III approach was performed as well to provide access to the most anterior aspect of the region. Anterior and posterior EAs were preserved bilaterally, and the fimbria was spared on the medialized mucosa. We divided the region into five corridors based on the ethmoidal arteries and the midline: two corridors are anterior to the anterior EA, two corridors are between the anterior and posterior EAs, and the fifth corridor corresponds to the planum sphenoidale. To have an objective data, we measured each corridor as if it was rectangular in shape, to calculate the approximate surface area of each one. With a tumor model made of polyurethane insulating foam less than 4 cm inserted via supraciliary or bifrontal craniotomies, we analyzed the feasibility of surgical removal of the tumor model.

Preliminary Results: In all 20 specimens, we were able to readily identify these corridors, as they are based on easily identifiable anatomic structures. The surface area of each corridor was, as expected, much smaller than the classical approach area (798 mm average). By using these corridors, we were able to fully expose and remove the tumor model from each specimen.

Preliminary Conclusion: For small tumors, these corridors offer a feasible approach to remove them without affecting the olfaction. For large tumors, the classical approach is better, especially that large tumors often manifest with preoperative anosmia. We still need to know how many corridors can be combined without affecting the olfaction.