The morphometric characteristics of the MEC have been widely studied, focusing on its prevalence, size, and clinical significance. While previous studies have reported the prevalence of MEC to range from 88.1% to 91.7% [3, 6, 9], it has been observed more frequently on the right side [3,4,5]. In our study, we observed at least one MEF in 92.15% of cases, which represents the highest prevalence reported in the literature. Additionally, we identified a unique case with six MEFs on the left side, which surpasses previous reports of up to four MEFs. Louis et al. (2009) classified the number of MEFs from 0 to 4 into five types (Type I: single, Type II: double, Type III: triple, Type IV: quadruple, and Type V: absent) [10]. In our study, most cases fell between Types I-III, with one case classified as Type IV, and the exceptional case with six MEFs remaining unclassified. Yurdabakan et al. (2023) reported that a single MEF was observed in 69.4% of cases, double in 10.3%, and triple in 1.6%, with no MEF present in 18.6% of cases. Quadruple MEFs were rare, appearing in only one case on the right side [11].

The clinical importance of accurately identifying and examining the MEF preoperatively cannot be overstated, given the significant variations in size, location, and course [1, 4, 6]. Enlarged MEFs have been associated with symptoms such as tinnitus [4, 12, 13], compressive scalp masses [14], thrombophlebitis [15], and facial swelling [16]. Also, a study by Ozen and Sahin [8] reported significantly larger MEF diameters in patients with chronic otitis media compared to controls, which is important for surgical planning.

In cases where the morphometric structure of the MEC is poorly understood, particularly when its diameter exceeds 3.5 mm, unexpected complications can arise during procedures such as mastoidectomy, epitympanectomy, and suboccipital craniotomy. These complications may include epidural and subdural hematomas resulting from unexpected bleeding [1]. In our study, six patients had at least one MEF with a diameter greater than 3.5 mm, a clinically significant threshold. According to the literature, the largest reported MEF diameters range from 4.5 mm to 8.9 mm [4, 10, 11, 17, 18]. In our sample, two patients had MEFs with diameters of 5 mm. Generally, an MEF with a diameter of 3.5 mm or greater is considered large [19]. Furthermore, the MEV canal is classified as prominent if its width exceeds 1 mm [20].

The variation in the number, size, and diameters of MEFs between individuals, and even between the right and left sides of the same patient, showed considerable standard deviations in our study. However, no statistical significance was found for these variations. Previous studies have reported varying average diameters of MEFs. Louis et al. (2009) evaluated cadaver heads and dried human skulls, reporting a mean MEF diameter of 3.5 mm, with a range of 1.1 to 5.6 mm [10]. Yurdabakan et al. (2023) analyzed 472 Cone-beam computed tomography (CBCT) images and found mean diameters of 3.39 ± 1.48 mm for the MEF and 2.05 ± 1.06 mm for the MEC, with males having larger mean diameters than females [11]. Similarly, Temiz et al. (2023) reported mean diameters of 2.4 ± 0.9 mm for the MEF and 2.1 ± 0.8 mm for the MEC, again noting significantly larger diameters in males [6]. In our study, we found a mean MEF diameter of 2.22 ± 0.80 mm on the right side in males and 2.17 ± 0.82 mm in females. On the left side, the mean MEF diameter was 2.18 ± 0.80 mm in males and 2.29 ± 0.78 mm in females. However, we did not observe significant differences in MEF diameters based on sex.

The morphology of the MEC has been explored using various imaging modalities, including MDCT [2, 7, 8], CBCT [6, 11], and magnetic resonance imaging [5, 21]. A study by de Oliveira-Neto et al. (2021) proposed a new classification system for MEF and MEV based on their three-dimensional morphology using MDCT [7]. The importance of using high-resolution imaging techniques such as MDCT or CBCT, prior to surgery has been highlighted due to the clinical implications of MEC variations and potential complications during surgical procedures [3, 6]. Roser et al. (2014) compared helical CT scans reconstructed using standard techniques (4.5-mm slices) with high-resolution techniques (1 mm) and found that the latter significantly improved the detection rate of emissary veins [22]. This difference in imaging techniques may explain some discrepancies between studies. In our study, the use of MDCT with a 1 mm voxel size enhanced the visualization of smaller anatomical structures. For example, Zhou et al. (2023) reported detecting MEFs in only 49.0% of patients using conventional CT scans, which had lower sensitivity [23]. In contrast, the high-resolution imaging in our study allowed us to identify a patient with six MEFs, surpassing previously reported maximums and highlighting the value of enhanced imaging techniques for detecting anatomical variations.

The strength of our study lies in the use of MDCT with a 1 mm voxel size and the employment of two experienced radiologists for measurements, which ensured reliability. However, as this was a retrospective observational study, it did not allow for the analysis of clinical outcomes related to the morphological and dimensional variations of MEFs. Further research is needed to explore recently proposed morphological classifications and to examine the relationship between MEF morphology and surgical complications.