High-resolution CT findings in children with a normal pinna or grade I microtia and unilateral mild stenosis of the external auditory canal

Congenital Aural Atresia: What the Radiologist Needs to Know?

Congenital aural atresia (CAA) is characterized by hypoplasia or aplasia of external auditory canal associated with auricular deformity. It also embodies a spectrum of temporal bone abnormalities including anomalies of middle ear, ossicles, facial nerve, oval window, round window, mastoid pneumatization, temporomandibular joint and occasionally inner ear and vascular anomalies. The management in such patients is variable and consists of rehabilitative hearing aids or surgical correction depending on various patient factors like associated temporal bone abnormalities, degree of hearing impairment and laterality. Surgical management if planned, depends on the extent of associated temporal bone anomalies and hence necessitates comprehensive knowledge about the normal and abnormal anatomy of these structures. High resolution computed tomography (HRCT) is the optimal investigation which provides required anatomical information and plays a pivotal role in deciding the management strategy. This pictorial review aims to review the spectrum of anomalies involving critical structures in CAA on HRCT along with their clinical significance.

Prevalence of middle ear malformation and outcomes of tympanoplasty and/or canalplasty in patients with and without congenital external auditory canal stenosis

OBJECTIVE

To compare the prevalence of middle ear malformations between patients with and without congenital external auditory canal stenosis (CEACS) and to investigate the outcomes of tympanoplasty and/or canalplasty in terms of tympanic membrane (TM) size and external auditory canal (EAC) stenosis in patients with middle ear malformation.

METHODS

Twenty-five patients who underwent primary tympanoplasty and/or canalplasty for middle ear malformation at a tertiary academic medical center were retrospectively reviewed. CEACS was defined as an EAC diameter of 4 mm or less. Intraoperative findings, including irregularity of the ossicles, facial nerve, or chorda tympani; size of the TM and EAC on computed tomography; and pre- and postoperative hearing level, were collected.

RESULTS

We included 7 and 18 patients with and without CEACS, respectively. The malleus handle defect, anterior deviation of the chorda tympani, and small TM (≤7 mm) (p-values 0.015, <0.001, and 0.003, respectively; Fisher's exact test) had significantly higher prevalence in patients with CEACS than in those without. The mean postoperative air-bone gap (ABG) in patients with CEACS was not significantly different from that in patients with normal-sized EAC (20.6 dB and 19.5 dB, respectively; p-value, 0.121; Mann-Whitney U test). No difference was observed in mean postoperative ABG between patients with small TM and those with normal-sized TM (19.2 dB and 20.0 dB, respectively; p-value, 0.469; Mann-Whitney U test).

CONCLUSION

Patients with CEACS were more likely to have malleus handle defect, anterior deviation of the chorda tympani, and small TM than those without CEACS. Hearing outcome of patients with CEACS and a malformed malleus and/or incus might be equivalent to that of patients without CEACS following tympanoplasty and/or canalplasty, regardless of the EAC or TM size.

Measurement method for external auditory canal and clinical application in congenital aural stenosis

OBJECTIVE

To describe a measurement method for external auditory canal (EAC), especially in congenital aural stenosis (CAS).

METHODS

High-resolution CT (HRCT) datasets of CAS were imported into the MIMICS 15.0 software for image processing. We used two methods to evaluate the degree of CAS. One is sagittal reconstruction measurement method, the minor axis of the bony ear canal was measured in each layer using sagittal reconstruction. The other is Matlab procedure calculation, we calculated the midpoint axis values of the EAC in each Frankfurt plane. Finally, we compared the minimum value of each method, and verified the sagittal reconstruction measurement method retrospectively in the CAS cases without cholesteatoma who had undergone meatoplasty.

RESULTS

Twenty CAS cases were selected using the sagittal reconstruction measurement method and Matlab procedure calculation to evaluate the degree of CAS. The mean age was 9.55 ± 2.85 years old (range: 6-15). The mean degree of CAS was 2.09 ± 0.50 mm by sagittal reconstruction measurement method and 2.03 ± 0.58 mm by Matlab procedure calculation. There were no significant differences in the two groups (t = -1.371, p = 0.186). A total of 94 HRCT datasets were imported into MIMICS for verification. The mean age was 11.66 ± 6.56 years old (range: 6-39). Mean stenosis of EAC at surgery was 2.88 ± 0.93 mm (range: 1-4) by using sagittal reconstruction measurement method.

CONCLUSIONS

Matlab procedure calculation is precise but relatively complicated and is only for scientific research. The sagittal reconstruction measurement method to calculate the most stenotic part of the bony ear canal is relatively simple and accurate to evaluate the degree of CAS. In cases of CAS without cholesteatoma, the precise measurement was critical for the next consultation.

High-resolution computed tomography evaluation of congenital aural atresia - how useful is this?

OBJECTIVE

To depict various temporal bone abnormalities on high-resolution computed tomography in congenital aural atresia patients, and correlate these findings with auditory function test results and microtia subgroup.

METHODS

Forty patients (56 ears) with congenital malformation of the auricle and/or external auditory canal were evaluated. Auricles were graded according to Marx's classification, divided into subgroups of minor (grades I and II) and major (III and IV) microtia. Other associated anomalies of the external auditory canal, tympanic cavity, ossicular status, oval and round windows, facial nerve, and inner ear were evaluated.

RESULTS

Minor and major microtia were observed in 53.6 and 46.4 per cent of ears respectively. Mean hearing levels were 62.47 and 62.37 dB respectively (p = 0.98). The malleus was the most commonly dysplastic ossicle (73.3 vs 80.8 per cent of ears respectively, p = 0.53). Facial nerve (mastoid segment) abnormalities were associated (p = 0.04) with microtia subgroup (80 vs 100 per cent in minor vs major subgroups).

CONCLUSION

Microtia grade was not significantly associated with mean hearing levels or other ear malformations, except for external auditory canal and facial nerve (mastoid segment) anomalies. High-resolution computed tomography is essential in congenital aural atresia, before management strategy is decided.

Anatomical measurement of the ossicles in patients with congenital aural atresia and stenosis

OBJECTIVES

Our aims were to measure and compare anatomical parameters of the ossicles in normal, congenital aural stenosis (CAS), and congenital aural atresia (CAA) ears.

METHODS

This retrospective study was performed using three-dimensional reconstructed images derived from computed tomography scans of 20 normal subjects, 20 CAS patients, and 20 CAA patients.

RESULTS

The lengths of the malleus handle and long process of the incus were greater in normal ears than in CAS and CAA ears (all P < 0.05). The angles of the incudostapedial joint and between the short and long processes of the incus were smaller in normal ears than in CAS and CAA ears (all P < 0.05). There were no significant differences in the positions of the malleus head and incudomalleolar joint, the size of the malleus head, the length of the short process of the incus, or the angle of the incudomalleolar joint (P > 0.05).

CONCLUSIONS

Anatomical parameters of the lower part, but not of the upper part, of the ossicular chain in CAS and CAA ears differed from those in normal ears. Different branchial arch origins of the upper and lower parts of the ossicular chain may explain these findings. Dysplasia of the second arch, which develops into the lower part of the ossicular chain, may contribute to ossicular malformation in CAA and CAS. Accurate radiographic measurement of malformed ossicles may be useful for reconstructive surgery of CAA and CAS using the patient's native ossicular chain and for choosing an appropriate place for active middle ear implants.