CT findings of the temporal bone in CHARGE syndrome: aspects of importance in cochlear implant surgery

Abstract

To provide an overview of anomalies of the temporal bone in CHARGE syndrome relevant to cochlear implantation (CI), anatomical structures of the temporal bone and the respective genotypes were analysed. In this retrospective study, 42 CTs of the temporal bone of 42 patients with CHARGE syndrome were reviewed in consensus by two head-and-neck radiologists and two otological surgeons. Anatomical structures of the temporal bone were evaluated and correlated with genetic data. Abnormalities that might affect CI surgery were seen, such as a vascular structure, a petrosquamosal sinus (13 %), an underdeveloped mastoid (8 %) and an aberrant course of the facial nerve crossing the round window (9 %) and/or the promontory (18 %). The appearance of the inner ear varied widely: in 77 % of patients all semicircular canals were absent and the cochlea varied from normal to hypoplastic. A stenotic cochlear aperture was observed in 37 %. The middle ear was often affected with a stenotic round (14 %) or oval window (71 %). More anomalies were observed in patients with truncating mutations than with non-truncating mutations. Temporal bone findings in CHARGE syndrome vary widely. Vascular variants, aberrant route of the facial nerve, an underdeveloped mastoid, aplasia of the semicircular canals, and stenotic round window may complicate cochlear implantation.

Keywords: Anatomy; CHARGE syndrome; Cochlear implant; Genetics; Temporal bone.

Fig. 1

Measurements in axial CT images. a Mastoid size A anterior-posterior (AP) size, measured in the middle of the external meatus (cranial/caudal) as the minimal distance from the external meatus to sigmoid sinus B lateral-medial (LM) size, distance between outer cortex and sigmoid sinus, measured perpendicular to A. b Angle cochlear basal turn. c Vestibulum size A longitudinal extension, B transversal diameter (right ear)

Fig. 2

Petrosquamosal sinus. Axial (a) and coronal (b) CT image of a right ear showing this emissary vein coursing along the lateral superior surface of the temporal bone. The petrosquamosal sinus originates at the transverse sinus and drains either into the retromandibular vein or the pterygoid venous plexus

Fig. 3

Examples of window stenosis. a Axial CT image showing stenosis of the round window niche (grey arrow) in a left ear. Note also dysplastic stapes on the promontory (white arrow). b–d Axial CT images showing atresia of the oval window (thin arrow), aberrant course of the facial nerve crossing the round window (arrowhead) and a dysplastic stapes positioned at the sinus tympani (thick arrow). Note aplasia of the semicircular canals

Fig. 4

Range of abnormalities of the cochlea seen in axial CT images. a Incomplete partitioning type II: normal development of the basal turn, but fusion of the second and apical turn seen in axial and coronal planes. b Hypoplasia type III: cochlea with less than 2 turns. c Cochlea type ‘IV’: the basal, second and apical turns are present, but the second turn seems shortened, giving the cochlea an asymmetric, flattened appearance

Fig. 5

Range of abnormalities of the vestibular system seen in axial CT images. a Aplasia of the semicircular canals in a right ear. b Dysplasia of the vestibule and semicircular canals in a left ear, with a malformed vestibule, shortened and dilated horizontal semicircular canal with small bony island, incomplete formation and dilatation of the posterior semicircular canal

Fig. 6

Cochlear aperture—axial CT image shows a lacking cochlear aperture

Fig. 7

Mastoid size—axial CT images of a small mastoid (a) and a wide mastoid (b); both ears had a grommet in situ