Stability of computed tomography densitometry in patients with otosclerosis:a two-year follow-up

Abstract

Objectives: To quantify the progression of otosclerosis in the unoperated ear between two stapedotomy procedures for patients with bilateral otosclerosis which can help to determine whether a HRCT scan should be re-performed before the second surgery for patients who already received HRCT imaging before the initial surgery.

Methods: 35 patients who underwent bilateral stapedotomy were included. Two rounds of HRCT examination and audiometry were performed at the time of the first surgery and second surgery on the ear that was not operated on during the initial surgery. The relationship between the changes in HRCT densitometry and audiometry over time was analyzed.

Results: The second round of HRCT did not add significant information about the changes to the otosclerosis lesions in either the imaging diagnosis or the HRCT density values except for small changes in the HRCT densitometry readings at the area anterior to the inner auditory (P = 0.01). While the changes in HRCT manifestation are small, changes near the fissula ante fenestram (FAF) were still positively correlated with the air bone gap (ABG) of patients (p = 0.031, r = 0.388).

Conclusions: The progression of lesions in otosclerosis is slow resulting in small and insignificant changes to the HRCT features. Therefore, a repeat HRCT evaluations prior to surgery is not necessary for patients who have had a previous HRCT evaluation within 2 years of the operation. The small changes in HRCT manifestation near the FAF were still correlated with negative effects on the ABG which could cause worsened hearing thresholds over this timeframe.

Keywords: Auditory; CT densitometry; Fissula ante fenestram (FAF); High reconstruction-computed tomography (HRCT); Otosclerosis.

Fig. 1

Example of the ROI setting. In the low axial section, 11 ROIs are manually placed. ROI 12 was located on the layer in which the niche of the round window was best shown. Mean CT values in each ROI could be measured automatically using the tool in the CT working station after selecting a 1mm2 ROI area.

Fig. 2

Presents the initial and final hearing levels in the cases of the normal group, the FAF group, and the cochlea group, respectively. The pre- and postoperative pure tone audiograms of the ears that underwent the initial surgery for these same patients is also presented. In figure a1, a patient from the normal group had a decrease in the BC threshold of 7.5 dB while the AC threshold was unchanged over the 3 years between audiograms. In figure b1, a patient from the FAF group showed an increase of 2.5 dB in their AC threshold while their BC threshold remain the same over the same time period. Lastly, in Figure c1, a patient in the cochlea group had an increase of 3.75 dB in both AC and BC hearing thresholds over a slightly shorter period of 2 years. L: left, R: right, pre-op: preoperative, post-op: postoperative.