Cog – A Radiological Indicator in Identifying Dysventilation Syndrome

Background: Anterior epitympanic recess (AER) is a small anatomical space in the epitympanum anterior to level of the head of malleus. This space has received lot of attention because of its role in cholesteatoma. Dysventilation of AER can lead to retraction pockets and cholesteatomas. Due to the advent of endoscopic middle ear surgeries the visualization of the mucosal folds and spaces have been possible for the past 2 decades. Mucosal folds and spaces play an important role in middle ear ventilation and pathologies obstructing these ventilation pathways can lead to dysventilation resulting in retraction pockets / cholesteatoma. In our study we have analysed the importance of cog with respect to dysventilation syndrome. Materials and methods: This prospective radiological study was conducted at Apollo Hospitals, BG road, Bangalore for a study period of 1 year (January 2021-January 2022). All patients who underwent high resolution CT scan (HRCT) of temporal bone were included in this study. They were divided into 2 groups (Group I & II). For group I HRCT temporal bone of 200 normal scans were included and scans with chronic otitis media, congenital anomaly, temporal bone fractures and tumors were excluded from the study. 50 HRCT temporal bone scans of chronic otitis media with squamous disease were included in group II. Results: 200 HRCT scans were included in the normative data analysis of the temporal bone. Out of 200, 133 had complete cog, 54 had incomplete cog and 13 had absent cog (Table 2). We also calculated the mean diameters of the AER, AP diameter- 4.24 ± 1.3, TD – 3.36 ± 1.05 and VD – 5.3 ± 1.94 (Table 3). Similarly, we analyzed 50 HRCT temporal bone with squamous disease 32 out of 50 had absent cog (Table 4). We also calculated the dimension of AER in diseased temporal bones (Table 5). A paired T test was conducted in order to analyze these values. Conclusion: In our study we performed a radiological evaluation of AER and cog and found that incidence of absent cog is more among individuals with squamous disease than normal individuals. Hence we advocate that absent cog can lead to horizontally oriented tensor tympani that in turn results in dysventilation.