Objective: To compare the development of temporal bone in normal and atretic ears and to assess some radiological landmarks that could be important in the hearing restoration interventions in such patients.
Material and methods: Thirty-five patients with 40 atretic external ears were evaluated with temporal bone CT and compared to a control group of 40 normal ears retrospectively. Using comparable slice levels in all patients, the course and the caliper of the facial canal, the surface area of the incus and malleus, the level of mastoid aeration, the location and anteroposterior diameters of the jugular bulb and sigmoid sinus, the direction and the caliber of the tympanic bony part of the Eustachian tube, area of the middle ear cavity, distance from facial nerve to incudomalleolar joint, to the vestibule and to the jugular bulb were included in the assessment. Non-parametric and parametric statistical tests were used for comparison.
Results: In atretic ears middle ear sectional area was found to be smaller at the equivalent plane as compared to control subjects (mean area index: 19.3mm(2) versus 47.4mm(2)). Mastoid aeration was low in general and the ossicles in the atretic ears were hypoplastic (mean ossicular sectional area: 8.3mm(2) versus 11 mm(2)). The distance from the jugular bulb to the facial nerve was significantly lower (mean: 6.2mm versus 6.8mm) (p<0.05) in the atretic ears. Facial canal caliber, distance from the facial canal to the incudomalleolar joint and distance from the facial canal to the vestibule in the atretic ears (means: 1.49, 2.93 and 1.82, respectively) did not show statistically significant difference from the control subjects (means: 1.44, 2.91 and 1.83, respectively) (p>0.05 for all).
Conclusion: External ear atresia is significantly associated with middle ear and mastoid abnormalities. The ossicles were underdeveloped which always have to be considered during reconstructive surgery. Radiologically, in the atretic ears anterior-posterior length of the temporal bone was more influenced as compared to superior-inferior portion, which justifies abnormal route of the facial nerve canal. However, there is no abnormality in the development of the facial nerve as the caliper is similar to the control subjects.