CBCT Assessment of Ethmoid Roof Variations through Keros, Gera, and TMS Classifications

Abstract

Background. This study is designed to assess the variations of the ethmoid roof through the Keros, Gera, and Thailand-Malaysia-Singapore (TMS) classifications by means of Cone-Beam Computed Tomography (CBCT). Materials and Methods. 372 CBCT scans were reviewed. The depth of the olfactory fossa (OF) was defined by the height of the lateral lamella (LL). The degree of the angle formed by the LL and the continuation of the horizontal plane passing through the cribriform plate was calculated. The risk of injury to the skull base was assessed by TMS classification. Results. The distribution of Keros types 1, 2, and 3 was 20.43%, 66.26%, and 13.31%, respectively. No significant difference was seen in the Keros classification among males and females, and asymmetry in the depth of the cribriform plate was seen in 33.3% of patients. 29.57% of the cases had type I, 61.42% had type II, and 9.01% had type III of Gera classification. 33.9% of the patients had asymmetry in the Gera classification. There was not significant difference in the Gera classification among males and females. 95.43%, 4.17%, and 0.40% of patients were of types 1, 2, and 3 of TMS classification, respectively. Conclusion. The most prevalent variations of the ethmoid roof were Keros type II, Gera type II, and TMS type 1. Although the prevalence of the dangerous types (Keros type 3, Gera type III, and TMS type 3) was low, preoperative assessment is essential in reducing surgical complications. CBCT is beneficial in evaluating these variations due to its low radiation dose.

Risk Factors for Anterior Skull Base Injury in Endoscopic Sinus Surgery

“…The present study showed that Gera Class II was the most common, followed by Classes I and III in Japanese patients, consistent with other studies in the Iranian, Turkish, Malaysian, and Italian populations (Table 5) [6,7,9,23,24]. The reason for the consistency in the proportion of Gera classes may be that the classification itself is new, and there are few reports from various countries.…”

“…Such variations in the distribution of Keros types may be attributed to several factors, including ethnic differences, genetic predisposition, environmental influences, prior chronic infections, and sample size. Patients classified under Keros Type III are notably more susceptible to iatrogenic injuries to the skull base due to the increased depth of the cribriform cleft [23,24].…”