Study of the Reliability of High Resolution CT Scan Evaluation of Eustachian Tube as Predictor of Predisposition for Chronic Otitis Media

Eustachian tube (ET) dysfunction is one of the predisposing factors for chronic otitis media (COM). This study looks at two parameters in High Resolution Computed Tomography of temporal bone namely tubotympanic angle (TTA) and pretympanic diameter (PTD) and its relationship with COM. The objectives of the study were to compare the tubotympanic angle and pretympanic diameter of the affected ear in patients with unilateral COM with that of healthy controls, and with contralateral non-COM ear. This was a retrospective study done at a tertiary referral hospital. Database of patients who underwent high resolution CT scan of temporal bone over a period of  three and half years, was studied. The TTA and PTD of ET were measured with the help of a senior radiologist well-versed in the imaging of temporal bone. Group A consisted of 45 patients with unilateral COM, while Group B comprised 50 patients without COM. Group A was further subgrouped as A1 (COM with cholesteatoma) and A2 (COM without cholesteatoma). The TTA and PTD in COM with cholesteatoma in the affected ear were 147.98 ± 5.89° and 2.84 ± 0.82 mm respectively, and in the unaffected ear, 144.81 ± 6.43° and 3.32 ± 1.19 mm respectively. In Group A, the TTA and PTD in the affected ear of unilateral COM were 146.17 ± 6.11°, 2.97 ± 0.87 mm and in Group B, it was 143.17 ± 6.01° and 3.48 ± 0.85 mm respectively. All these were statistically significant (p value < 0.05). Increased TTA and reduced PTD of ET may be a predisposing factor for the development of COM and cholesteatoma.