The Evaluation and Measurement of Anterior Ethmoidal Canal in Axial OMU CT / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The anterior ethmoid canal is the important surgical landmark in endoscopic sinus surgery, intranasal ethmoidectomy, and frontal sinus surgery. However it is not enough to evaluate the anterior ethmoid canal by coronal OMU CT, especially relating anterior to posterior relationship of the anterior ethmoid canal. The pulpose of this study is to evaluate the anterior ethmoid canal in 1 mm axial OMU CT and measure the five parameters relating the anterior ethmoid canal. MATERIALS AND METHODS: A prospective study was performed in 100 sinuses of 50 patients with chronic sinusitis who underwent endoscopic sinus surgery from May through July of 1998. RESULTS: The anterior ethmoid canal is well demonstrated by 1 mm axial OMU CT. The average of five parameters are 6.2+/-1.5 mm, 6.4+/-4.3 mm, 18.5+/-3.9 mm, 26.5+/-5.6 mm, 24.6+/-14.6degrees. However, there is no difference between the right and left side statistically. We observed that the anterior ethmoid canal is located just posterior to the frontal recess without anterior ethmoid air cell in front of the antirior ethmoid canal in 23%. CONCLUSION: The anterior ethmoid canal is well remarked by the 1 mm axial OMU CT. The length and directional angle of the anterior ethmoid canal is individually variable and there is no anterior ethmoid air cell in front of the anterior ethmoid canal in 23%. In these cases, the anterior ethmoid canal is more likely to be injured. So axial OMU CT may be useful in the radiologic evaluation for endoscopic sinus surgery in chronic sinusitis.

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

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.