Anatomical Relationship of the Anterior Ethmoid Canal to the Anterior Skull Base: A Computed Tomographic Analysis on the Types of the Fovea Ethmoidalis

Hong, Soon Kwan; Eum, Jun Hyung; Byun, Sung Wan; Kim, Chong Nahm; Kim, Chun Dong; Chung, Seung Yong; Chang, Ju Ae; Choi, Hae Young

Abstract

BACKGROUND AND OBJECTIVES: As the anterior ethmoid canal (AEC) provides a good surgical landmark and its injury may result in serious complications, the anatomical relationship of the AEC to the anterior skull base (ASB) should be evaluated preoperatively. Despite some studies on the ASB, studies analyzing this anatomical relationship and the types of the fovea ethmoidalis (FE) on computed tomography (CT) are rare. The aim of this study is to better understand this anatomical relationship by determining the frequency of each type of the FE and distances between anatomical structures on the CT scans with our new classification. MATERIALS AND METHOD: Four hundred sides of the FE were analyzed from the preoperative coronal CT scans of 200 chronic sinusitis patients (100 males and 100 females, aged 20 to 59 years). The FE was classified into 4 types (I: non-separated type, II: partially separated type, III: completely separated type, IV: unidentifiable type) and 2 subtypes (A: developed medial cranial wall, B: undeveloped medial cranial wall). Heights of the medial cranial wall (a), the AEC (b), and the ethmoid roof (c) were measured on the CT image.
RESULTS
Frequencies of the types I-IV were 48.0% (IA: 25.2%, IB: 22.8%), 19.3% (IIA: 4.3%, IIB: 15.0%), 29.5% (IIIA: 29.5%, IIIB: 0%), and 3.2%, respectively. The medial cranial wall of type IIIA was significantly longer than those of the other types, and the AEC of type IIIA was in a significantly lower position than those of the other types.
CONCLUSION
On the CT scans, we found the AEC in 96.8% and type IIIA in nearly 30% of all types of the FE. Sinus surgery should be performed only after preoperative evaluation of these anatomical relationship on the CT scans under close scrutiny. For the type IIIA, surgery should be performed with utmost care due to high risk of injury to the AEC and the medial cranial wall.