Anatomic Variants on Computed Tomography in Congenital Aural Atresia

Abstract

A large obstructing MIC increases difficulty of atresiaplasty. Awareness of the presence of these anatomic variants is an aid in teaching temporal bone anatomy and may possibly influence the decision regarding atresiaplasty.

High-Resolution CT Findings in Children with a Normal Pinna or Grade I Microtia and Unilateral Mild Stenosis of the External Auditory Canal

“…Only 1 patient in this series had a mild anteriorly positioned mastoid segment. The obstruction of access to the oval window by the anterolateral displacement of the vertical segment of the facial canal was reported in 41% of patients with atresia in the series by Dedhia et al 11 The abnormal position of the facial nerve could potentially increase the risk of injury to the nerve. There were no anomalies of the tympanic segment of the facial nerve canal in this series, which would have precluded surgical access to the oval window.…”

“…8 HRCT of the temporal bone was evaluated for findings based on the criteria developed by Jahrsdoerfer et al 9 for identifying suitable candidates with congenital aural atresia for surgery. 10,11 The presence of ossicular anomalies, including fixation, abnormal position, and abnormal shape or size, was noted. Fixation was defined as the presence of an osseous bar between the ossicles and the margins of the middle ear cavity or when the ossicles were not separable from the walls of the middle ear cavity.…”

The extent of inferior displacement of the mastoid tegmen is related to the severity of congenital aural atresia

“…Straight mastoid drilling is used during atresiaplasty to access the middle ear cavity and the malleus-incus (MI) complex [6]. The most important obstacle to straight mastoid drilling is inferior displacement of the mastoid tegmen [7]. The extent of inferior displacement of the mastoid tegmen rises in proportion to the severity of CAA.…”

“…High-resolution temporal bone computed tomography (TBCT) analysis is currently the most important radiological test for standard preoperative evaluation before atresiaplasty [7][8][9][10][11][12]. TBCT analysis is based on the grading system developed by Jahrsdoerfer et al [13].…”

“…The grading system consists of nine factors of surgical importance: presence of stapes, open oval window (OW), open round window (RW), aerated middle ear space, presence of the MI complex, pneumatization of the mastoid, continuity of the incudostapedial (IS) joint, normalcy of the course of the facial nerve, and normal appearance of the external ear [13]. However, some studies suggest that other factors such as the extent of inferior displacement of the mastoid tegmen and the size of the IS joint angle have an additional and considerable bearing on the surgical outcome after atresiaplasty [7,14]. In view of these findings, a modification of the Jahrsdoerfer grading system has been published with 2 points awarded to the inferior displacement of the mastoid tegmen; more than 25% of middle ear height displaced tegmen was observed on the TBCT scan in 17% of CAA cases [7].…”