Measuring the density of the fissula antefenestram and the section of the basal turn of the cochlea: Are they useful in the radiological diagnosis of otosclerosis?

Abstract

Introduction: The role of objective parameters in terms of improvement of the accuracy of high-resolution computed tomography (HRCT) of the temporal bone in the diagnosis of otosclerosis remains unclear.

Objectives: To investigate the relationship between the density of the fissula antefenestram (FAF) and of the width of the transversal section of the basal turn of the cochlea (BTC), and the diagnosis of otosclerosis.

Methods: This is a retrospective study in which preoperative HRCT data from ears of patients submitted to stapedotomy due to otosclerosis (case group) were evaluated. For the control group, normal hearing ears having undergone HRCT for other purposes were included. Case and control HRCT images were objectively assessed by an experienced blinded radiologist. During this evaluation, measurements of the relative radiological density of the FAF and of the transversal section of the BTC were obtained. The results were compared between the groups. Also, a receiver operating characteristic curve was created and the area under the curve (AUC) was calculated for each variable. Significance level was set at .05.

Results: 40 ears were included in each group. Case ears presented reduced values for the relative radiological density on the FAF (p-value<0.0001). Moreover, ears with otosclerosis (p-value: 0.022) presented lower transversal section of the BTC. The AUC for these variables reached 0.929 and 0.646, respectively.

Conclusions: Otosclerotic ears present reduced radiological density on the FAF and narrower BTC. The relative density of the FAF also shows a great diagnostic power in the context of this disease.

Keywords: Computed tomography; Imaging diagnosis; Otosclerosis.

Fig. 1

HRCT scan images of the right temporal bone showing the measurements of the radiological density of a region of interest of 0.01 cm² (black arrows). A: in the plane of the oval window, for the antefenestral measurement. B: in the plane of the zigomatic arch, for the most posterior high-density area of this bone.

Fig. 2

Axial section of a HRCT scan of the temporal bone showing the measurement of the transversal basal turn of the cochlea (black arrow).

Fig. 3

Study flow chart. Legend: n: number; HRCT: high-resolution computed tomography; CT: computed tomography; FAF: fissula antefenestram.

Fig. 4

Distribution of the results obtained for each variable of the study, according to the allocation group. A: relative density of the fissula antefenestram. B: Transversal section of the basal turn of the cochlea. Legend: mm: millimeters; FAF: fissula antefenestram.

Fig. 5

ROC curves showing the diagnostic ability of the transversal section of the basal turn of the cochlea and for the relative density of the FAF to discriminate individuals with otosclerosis using HRCT scans. Legend: FAF: fissula antefenestram.