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AJR:194, March 2010 WS3

Congenital Sensorineal Hearing Loss

(but not larger than) the bone width between the lateral

vestibular wall and the inner wall of the lateral semicircular

canal. The internal auditory canal should be larger than 2

mm; a smaller diameter has been shown to adversely impact

the long-term outcome with cochlear implantation. A small

internal auditory canal can indicate absence or small size of 

the cochlear nerve, which is best further evaluated with

MRI [4, 5] (Fig. 4).

Some controversy exists about the classication of coch-

leovestibular malformations [6]. Especially the widespread

use of the term “Mondini malformation” has been subjectto scientic debate and has been differentiated into two

types of incomplete partitioning (IP), IP-I and IP-II. The

following classication and denitions have been proposed

by Sennaroglu and Saatci [6], listed here in descending or-

der of severity: labyrinthine aplasia, “Michel deformity,”

no inner ear structures have formed; cochlear aplasia, ab-

sence of cochlea; common cavity, single cavity of cochlea

and vestibule; IP-I, cystic cochlea and cystic vestibule; co-

chlear hypoplasia and cochlea with less than 2.5 turns (Fig.

5); and IP-II, Mondini deformity, incomplete partition be-

tween the middle and apical turns of the cochlea forming a

cystic apex, normal basal turn, large vestibular aqueduct,

and enlarged vestibule (Fig. 1).The correct identication of inner ear pathology helps

assessment for contraindications to cochlear implantation

A

Fig. 5—Companion case in 2-year-old girl withhypoplastic cochlea.A, High-resolution CT image reormatted in coronalplane at level o cochlea shows hypoplastic rightbasal turn o cochlea (arrow ); middle and apical turnshave not ormed.B, High-resolution CT image reormatted in coronalplane at level o cochlea in healthy 3 -year-old boy isshown or comparison.

B

A

Fig. 4—Companion case in 5-year-old girl withhypoplastic internal auditory canal.A–C, Axial FIESTA (ast imaging employing steady-state acquisition) MR image (A) and sagittalreormations perpendicular to long axis o internalauditory canal (B and C). In axial FIESTA MR image,note abnormally small size o right internal auditorycanal compared with let (1.8 vs 3.2 mm). Sagittalreormation on right (B) shows absence o cochlear

nerve in expected anterior inerior location (arrow, B) as seen on contralateral side (long arrow, C). Notecranial nerve 7 normally visualized on let side inanterior superior portion o internal auditory canal(arrowhead, C) and normal superior and ineriorvestibular nerves posteriorly (small arrows, C).

CB

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Kadom and Sze

WS4 AJR:194, March 2010

and improves surgical planning. Successful cochlear implant

function requires functionality of the cochlear nerve and at

least some residual auditory cells. A small internal auditory

canal seen on CT can be an indirect sign of cochlear nerve

absence or hypoplasia, as conrmed by Glastonbury et al.

[7] by MRI correlation. However, deciency of the cochlear

nerve can exist in the setting of a normal size internal audi-tory canal, probably due to an insult that occurs after for-

mation is complete [7]. Some authors prefer high-resolution

MRI over high-resolution CT because it simultaneously

provides information about cochlear patency and presence

and size of the cochlear nerve [4]. Absence of the cochlea

and labyrinthine (Michel) aplasia are contraindications for

cochlear implant surgery. Cochlear dysplasia, although it

limits full insertion of the implant electrodes, still will yield

benet to the patient because of the residual auditory cells

present. Precise radiologic information also affects surgical

planning. For example, in the presence of a dysplastic co-

chlea there may also be a thinner barrier between the co-

chlea and subarachnoid space, which increases the risk of CSF leak, intracranial electrode insertion, and meningitis.

However, this can be surgically addressed by choosing an

appropriate electrode and imaging conrmation of correct

placement. CSF leak requires packing of the cochleostomy

site. Description of facial nerve position is important be-

cause an aberrant position may pose an increased risk of 

facial nerve injury and requires more careful surgical tech-

nique and facial nerve monitoring [8].

Clinical ManagementThe audiology assessment showed bilateral moderate to

profound sensorineural hearing loss, left worse than right. The

patient received bilateral temporary hearing aids to bridge thetime to cochlear implantation. Extensive speech and language

testing was performed preoperatively and showed the patient

had a good foundation for auditory skills. The patient received

a left cochlear implant and postoperative follow-up implant

mapping showed excellent acoustic benet.

CommentaryThe incidence of sensorineural hearing loss in children is

about one in 1,000. Today, screening tests as part of new-

born evaluations facilitate the early detection of congenital

hearing impairment [9]. Cochlear implants bypass inner ear

dysfunction from structural abnormalities by direct elec-

trode activation of auditory nerve bers that reside in thecochlea with an electrode, thus improving hearing and sub-

sequent speech development [9]. There is emerging knowl-

edge that bilateral cochlear implants are benecial for de-

velopment of 3D sound localization when implanted within

the rst 3 years of life [9].

High-resolution CT plays a vital role in the diagnosis of 

congenital sensorineural hearing loss and helps with surgical

decision making and planning, as discussed earlier. However,

additional imaging techniques are used in the pre- and post-operative evaluation of cochlear implant patients, and there

are additional applications for CT of the temporal bones in

this patient group. For example, it has been shown that pre-

operative functional studies of auditory response with MRI,

PET, or SPECT can provide useful information on brain ac-

tivity response to auditory stimuli. This, in turn, can help in

deciding the side of a single cochlear implant and help pre-

dict functional outcome after implantation [4]. Given that

most implant devices are not compatible with magnetic eld

exposure, the preferred methods for postoperative functional

auditory assessment are PET and SPECT [4]. CT can play an

additional role in postoperative assessment of the electrode

position [10]. Modern imaging protocols, such as BrainLab(BrainLAB), can be used for 3D planning of minimally inva-

sive surgery, using the imaging data to plan a drill path. Fur-

ther studies using this technique are under way at the Na-

tional Institutes of Health [11].

References1. St. Martin MB, Hirsch BE. Imaging o hearing loss. Otolaryngol Clin North

 Am 2008; 41:157–178 [vi-vii]

2. Lowe LH, Vézina LG. Sensorineural hearing loss in children. RadioGraphics  

1997; 17:1079–1093

3. Som PM, Curtin HD. Head and neck imaging, 4th ed. St Louis, MO: Mosby,

2003

4. Pappas DG Jr, Curé JK. Diagnostic imaging. Otolaryngol Clin North Am 2002;

35:1317–1363 [ix]

5. Wu CC, Lee YC, Chen PJ, Hsu CJ. Predominance o genetic diagnosis and

imaging results as predictors in determining the speech perception perormance

outcome ater cochlear implantation in children.   Arch Pediatr Adolesc Med  

2008; 162:269–276

6. Sennaroglu L, Saatci I. A new classifcation or cochleovestibular malorma-

tions. Laryngoscope 2002; 112:2230–2241

7. Glastonbury CM, Davidson HC, Harnsberger HR, Butler J, Kertesz TR, Shel-

ton C. Imaging fndings o cochlear nerve defciency. AJNR 2002; 23:635–643

8. Francis HW, Niparko JK. Cochlear implantation update. Pediatr Clin North Am 

2003; 50:341–361 [viii]

9. O’Leary S, Chang A. Hearing impairment: technological advances and in-

sights. Aust Fam Physician 2008; 37:322–327

10. Verbist BM, Frijns JH, Geleijns J, van Buchem MA. Multisection CT as a valu-

able tool in the postoperative assessment o cochlear implant patients.  AJNR 

2005; 26:424–429

11. Labadie RF, Noble JH, Dawant BM, Balachandran R, Majdani O, Fitzpatrick JM. Clinical validation o percutaneous cochlear implant surgery: initial report.

 Laryngoscope 2008; 118:1031–1039

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