The Anterior Olfactory Cleft: An Area of Weakness Caused by the Ethmoidal Fissure

Objective: The olfactory cleft (OC) has gained some interest since the advent of endoscopic skull base surgery. However, its precise anatomy is still partially unknown. In the early 20th century an “ethmoidal fissure (EF)” has been described by Rouvière and Gray but without enough details to help surgery. According to the authors, the EF would be located at the anteromedial part of the OC and would contain a process of dura. More laterally a second foramen, the “anterior ethmoidal slit (AES),” would contain the anterior ethmoidal nerve. The aim of this study was to verify the existence of those elements and to establish landmarks for endoscopic surgery. Study Design and Methods: An anatomic study was conducted. We performed an anatomical and histological study of eight OC in three males and one female fresh cadavers, respectively, using superior endocranial and endoscopic dissection. Results: An EF and an AES were found in 100 and 75%, respectively, of the OC analyzed. They measured 4 mm (±1.22) and 1.75 mm (±0.55)in their higher length, respectively. The EF and AES were located at 5.25 mm (±1.49) and 5.8 mm (±1.17), respectively, from the anterior ethmoidal artery (AEA), which appeared to be the most constant landmark. This allowed us to describe a risk area located 2.8mm anterior to the AEA. Histological analysis of the EF found a connective tissue lacking specific characteristics to identify dura. Conclusions: Our anatomical study demonstrates the existence of both foramina. The EF clearly represents an area of weakness at the anterior part of the olfactory cleft, which could predispose to anterior skull base CSF leaks and meningoceles.