Congenital malformations of the inner ear can affectany portion of the membranous or the bony labyrinth. Aprimary or secondary deficiency of the cochlear nervemay also present as a congenital anomaly. CT and MRIallow for a detailed analysis of each lesion and they canprovide guidance for the proper treatment of each pa-tient. Both CT and MR imaging can be used to detect in-ner ear malformations, yet the two techniques are often

complementary. CT is preferred in those cases whereassociated middle or external ear malformations mustbe excluded. MRI is preferred in the case of evaluatingsubtle changes in the membranous labyrinth or wherethere are abnormalities of the nerves in the internal au-ditory canal (1-5).

We describe here the CT and MRI findings for a vari-ety of deformities of the osseous labyrinth involving thecochlea, vestibule, semicircular canal, internal auditorycanal, and vestibular aqueduct in patients sufferingfrom congenital sensorineural hearing loss.

Embryology

Most temporal bone anomalies are caused by the pre-

J Korean Radiol Soc 2005;52:165-171

─ 165 ─

Inner Ear Anomalies Causing Congenital SensorineuralHearing Loss: CT and MR Imaging Findings1

Hyun Sook Hong, M.D., Sang Hyun Paik, M.D., Jang Gyu Cha, M.D.,Seong Jin Park, M.D., Joon Hee Joh, M.D., Jai Soung Park, M.D.,Dae Ho Kim, M.D., Hae Kyung Lee, M.D., Shi-Chan Kim, M.D.2

Many congenital dysplasias of the osseous labyrinth have been identified, and thedifferential diagnosis of these dysplasias is essential for delivering proper patient man-agement. We retrospectively reviewed the computed tomography (CT) and magneticresonance (MR) imaging findings of 20 children who had congenital sensorineuralhearing loss. The children included cases of enlarged vestibular aqueduct and en-dolymphatic sac (n=8), aplasia of the semicircular canal (n=4), lateral semicircularcanal-vestibule dysplasia (n=3), common cavity malformations with a large vestibule(n=1), cochlear hypoplasia (n=1), Mondini’s dysplasia with large vestibular aqueduct(n=1), Mondini’s dysplasia with a large vestibule (n=1), and small internal auditorycanal (n=1). Six cases were unilateral. Nine cases had combined deformities, and ninecases had cochlear implants. CT was performed with a 1.0-mm thickness in the directcoronal and axial sections with using bone algorithms. MR was performed with a tem-poral 3D T2 FSE 10-mm scan and with routine brain images. We describe here theimaging features for the anomalies of the inner ear in patients suffering from congeni-tal sensorineural hearing loss.

Index words : Ear abnormalitiesComputed tomography (CT)Magnetic resonance imaging (MR)

1Department of Radiology, Soonchunhyang University Bucheon Hospital2Department of Otorhinolaryngology, Soonchunhyang UniversityBucheon HospitalReceived February 16, 2004 ; Accepted March 8, 2005Address reprint requests to : Hyun Sook Hong, M.D., Department ofRadiology, Soonchunhyang University Bucheon Hospital, 1174 Jung-dong, Wonmi-gu, Bucheon-si, Gyeonggi-do, 420-021, Korea.Tel. 82-32-621-5846 Fax. 82-32-621-5874 E-mail: hshong@schbc.ac.kr

mature arrest of development or by the complete failureof formation (1, 6). Congenital malformations tend to in-volve either the inner ear or the middle and external ear.In some craniofacial syndromes or chromosomal disor-ders, anomalies of both regions do occasionally coin-cide. Embryopathies that are due to toxin exposure mayalso result in combined anomalies (1, 2, 4, 7-9).

The inner ear develops between the 4 th week and 8th week of gestation, it grows between the 8 th and 16 thweeks and it ossifies between 16 th and 24 th weeks.Malformation of the inner ear results from arrest duringthe various stages of embryogenesis. The cochlear ductdevelops first and cochlear malformations range fromcomplete aplasia, which generally develops at the 3 rdweek, to incomplete partition or a cochlea with incom-plete or no interscalar septa, and this generally developsat the 7 th week. Cochlear development is complete atthe 8th week. The saccule, endolymphatic duct and utri-cle are completed at 11 weeks and the semicircularcanals (SCC) develop between the 19th and 22nd weeks.The lateral SCC or duct is the last to form and thus, it ismost frequently affected (6-9).

Michel’s Anomaly

Michel’s anomaly, complete labyrinthine aplasia, iscaused by early arrest of differentiation of the otic pla-code during the 3rd gestational week (6). The diagnosiscan be made when the inner ear structures are absent.

Labyrinthitis ossificans (Fig. 1A, B) may have a similarappearance, but for this acquired disorder, the generalshape of the formed labyrinth is preserved, and the me-dial wall of the middle ear bulges over the lateral SCCand the cochlear promontory. In labyrinthine aplasia,the middle ear medial wall is flat and featureless.

Common Cavity Malformation

Developmental arrest between the 4 th and 5 th gesta-tional weeks results in a single labyrinthine structurethat is called a common cavity. This is seen as a singlefluid-filled space in the bony otic capsule, and it is with-out the internal cochlear or vestibular differentiation(Fig. 2A-C). The SCC or vestibule can be normal ormalformed. In these patients, the internal auditory canal(IAC) can be recognized, unlike the patients with com-plete labyrinthine aplasia. One fourth of all cochlearmalformations are common cavity malformations.

Cochlear Aplasia or Hypoplasia

Arrest of cochlear development during the 5-6 thweeks results in cochlear aplasia and hypoplasia (6). Incochlear aplasia, the cochlea is seen as a single cavitywithout seperation of the different turns and the cochleais also without distinguishable scala vestibuli/scala tym-pani. The vestibule and SCC can be normal, althoughthey are most often malformed or only their remnantsare seen. One turn or less is generally noted in cochlearhypoplasia (Fig. 3A). Cochlear hypoplasia represents15% of all cochlear malformations. These malforma-tions are often found in patients with brachio-oto-renalsyndrome. Cochlear aplasia and hypoplasia display as adysmorphic cochlear cavity with no discrete internalcochlear architecture, and there are often coexistingvestibular anomalies (Fig. 3B). Dysplastic changes of thevestibule may be seen as a bulbous enlargement.

Hyun Sook Hong, et al : Inner Ear Anomalies Causing Congenital Sensorineural Hearing Loss

─ 166 ─

A

BFig. 1. A. Labyrinthitis ossificans. Axial CT scan of the innerear in a 7-year-old boy with a history of bacterial meningitis,and he suffered from a progressive and profound sensorineur-al hearing loss. Near complete osseous obliteration of thecochlea is apparent and only a basal turn (arrows) remains.B. 3 D FSE MRI shows complete absence of a fluid signal (ar-row) in the expected location of the cochlea and the SCC.

Incomplete partition of the cochlea (Mondini malforma-

tion)

Incomplete partition of the cochlea (Mondini malfor-mation) occurs when cochlear development is arrestedduring the 7 th week of gestation. This malformation ac-counts for 55% of all cochlear malformations. In thesepatients, the cochlea has only 1.5 turns, and often thereis preservation of the basilar turn while the interscalarseptum and osseous spiral lamina are absent (Fig. 4A,B). Other features of mild dysplasia include a deficientmodiolus and an incomplete interscalar septum alongwith the asymmetric or undivided scalar chambers (4).

The interscalar septal defect and the absence of the os-seous spiral lamina of the middle ear and the apicalturns can best be demonstrated on heavily T2- weightedgradient -echo images or on the fast spin echo images.Incomplete partition is often associated with a large en-dolymphatic duct (ELD) and the sac and vestibularaqueduct.

Overall, the vestibule, SCC and ELD/sac malforma-tions are found in 20% of these patients (Fig. 5A, B). Dueto the variable development of the sensory neuroepithe-lium, there are various degrees of sensorineural hearingloss noted for these patients.

Vestibular Dysplasia

The saccule and utricle are completely formed at the11 th week of gestation. Isolated malformations of thevestibule are rare and these malformations are most of-ten associated with other inner ear malformations suchas SCC anomalies or cochlear anomalies (Fig. 2). TheSCC can be partially or completely assimilated in thevestibule, and the vestibule can be enlarged and irregu-larly shaped. There appears to be a reciprocal relation-ship between the size of the SCC, particularly the lateral

J Korean Radiol Soc 2005;52:165-171

─ 167 ─

A

BFig. 3. A. A 6-year-old boy with right cochlear hypoplasia. Theaxial 10-mm-thick T2-weighted 3 D FSE image shows only asmall basal turn (arrow) of the right cochlea.B. A short, broad lateral semicircular canal is confluent withthe vestibule, and together, they form a single fluid-filled cavi-ty (arrows).

B

A

CFig. 2. An 8-year-old boy with a left common cavity malforma-tion.A. (axial scan) and B (coronal CT scan). A single cavity (ar-rows) is found in the inner ear, and this represents the cochleaand the vestibule. This cavity is called a “common cavity”. TheIAC is visible.C. Axial 10-mm-thick 3 D FSE T2-weighted image at the levelof the cochlea (arrows).

canal, and the size of the vestibule. An enlargedvestibule is associated with an underdeveloped lateralSCC.

This malformation is the the second most commonlyobserved isolated deformity (Fig. 6A, B). In its mildestform, the lateral SCC, as a whole, is smaller than normaland the vestibule is slightly larger than normal. In itsmore severe forms, the vestibule extends further intothe lateral and superior aspects of the otic capsule. Theinternal diameter of the vestibule is measured at the lev-el of the lateral SCC and the width and length measure-ments are made at the mid-portion. The vestibule is con-sidered abnormally enlarged if the width is >3 mm andlength is >6 mm (4).

Semicircular canals/ducts

A malformation of a SCC that’s associated with a nor-mal cochlea is most likely to be due to a problem occur-ring between the 7 th and 22 nd week of gestation. Anopen pouch persists in the most common SCC anomaly,and lesser degrees of these SCC anomalies are represent-ed by segmental dilatation on parts of the canal. The lat-eral SCC develops last and is the most likely to be abnor-mal, and the superior SCC is the least likely to be mal-formed. Dilatation of the lateral SCC is often accompa-nied by dilatation of the vestibule (Fig. 6), and this is oc-casionally detected as an incidental finding. Isolate apla-sia of the posterior SCC has been described in patientswith Waardenburg and Alaagille’s syndromes (10). Thediagnosis of ‘CHARGE’ syndrome (abnormalities of thecoloboma and heart, choanal atresia, retarded growth,and abnormalities of the genitals and ear) is nearly cer-

Hyun Sook Hong, et al : Inner Ear Anomalies Causing Congenital Sensorineural Hearing Loss

─ 168 ─

A

BFig. 6. A 1-year-old boy with lateral SCC-vestibule dysplasia.The axial (A), and coronal (B) scans show the vestibule is en-larged and it extends into the region of the otic capsule that isnormally occupied by the lateral semicircular canal. The later-al SCC and vestibule form a single cavity (arrow). The normalposterior SCC (arrowhead) is seen.

A B

Fig. 4. A 2-year-old boy with bilateralMondini dysplasia and a largevestibule. The axial CT (A) and thecoronal (B) scans of the right ear showshortening of the cochlea (arrows)along its modiolar axis and the inter-scalar septum is not visualized.

A B

Fig. 5. A 3-year-old girl with bilateralMondini dysplasia and an enlargedvestibular aqueduct.A. The vestibular aqueduct (arrows) isenlarged, funnel shaped and widelyopened.B. In addition, insufficient cochlearturns (arrows) are seen.

tain when aplasia of all the SCCs/ducts is found (Fig. 7A,B).

A large endolymphatic duct and sac (LEDS)

A large endolymphatic duct and sac (LEDS) consti-tutes enlargement of the endolymphatic sac and ductand there is corresponding enlargement of the bonyvestibular aqueduct (VA) (Fig. 8) (8, 12). The VA or en-dolymphatic duct are considered enlarged when theirdiameters exceed that of the posterior SCC or when theyare more than 1.5 mm in diameter, as measuredhalfway between the common crus and the externalaperture of the VA (7).

The diameter of the VA in normal temporal bones is0.4-1.0 mm. LEDS is the most commonly identified ra-diographic anomaly of the inner ear (6, 13, 14). It hasbeen found that 1-1.5% of the cases referred for tomog-raphy of the inner ear structures have an abnormallylarge VA. Patients typically present with a progressive,severe sensorineural hearing loss in childhood or earlyadulthood, and this condition is often exacerbated byminor trauma (13, 15). The majority of patients have amixed sensorineural/conductive hearing loss. Patientswith a LEDS have an associated cochlear malformationin 76% of cases (Fig. 5) and there is vestibular malforma-tion in 40% of cases (5, 11). Vertigo is present in 30% ofcases. Any correlation between the severity of the radio-logical abnormality and the associated clinical symp-

toms is unclear. The mechanism by which LEDS causesprogressive SNHL is still unknown.

Several possible mechanisms of cochlear damage havebeen proposed, and these include injury caused by pres-sure effects, physiologic endolymphatic dysfunction andsusceptibility to minor trauma (5, 13). The high preva-lence of coexisting cochlear anomalies is probably amanifestation of a common underlying embryologic in-sult.

Small Internal Auditory Canal

The internal auditory canal (IAC) is usually normal,but it may be large or small in association with the innerear anomalies. Aplasia or severe narrowing of the IAC isassociated with sensorineural hearing loss (Fig. 9). Anenlarged IAC, due to dural ectasia, has been describedin neurofibromatosis.

Congenital stenosis of the IAC may exist as an isolatedcondition or it is noted along with a number of other os-seous anomalies of the temporal bone. Isolated narrow-ing of the IAC implies that there is an otherwise radi-ographically normal otic capsule and the absence of anyosseous condition predisposing the patient towards ac-quired stenosis (5). A history of significant head trauma

J Korean Radiol Soc 2005;52:165-171

─ 169 ─

A

BFig. 7. An 11 month-old boy with CHARGE syndrome. The ax-ial (A) and coronal (B) scans show aplasia of the entire SCC (ar-row).

Fig. 8. An 11-year-old boy with bilateral large endolymphaticsacs. The axial 7-mm thick, T2-weighted, 3 D FSE imageshows that the endolymphatic sacs (arrows) have larger diam-eters than the ascending segment of the posterior SCC (arrow-head). The vestibule and lateral SCC appear normal.

Fig. 9. A 1-year-old girl with a small internal auditory canal (ar-rows) and a large vestibule. The CT scan shows the decreaseddiameter of the internal auditory canals bilaterally.

should also be excluded. The development of the IAC isseparate from that of the labyrinth.

The normal range of IAC diameters has long beenquoted as being 2-8 mm with an average of 4 mm, andthese numbers are based on Valvassori’s series. An IACsmaller than 2 mm is considered stenotic. MRI is poten-tially sensitive enough to demonstrate the 4 distinctnerve bundles in the IAC (5). Aplasia of the cochlearnerve is manifested as a loss of the normal round fillingdefect in the antero-inferior IAC. Due to the concomi-tant embryologic development of the IAC and thenerves, congenital aplasia is also accompanied by astenotic IAC. A stenotic IAC is often associated with theabsence of the vestibulocochlear nerve, and this is acontraindication for cochlear implantation (5, 9, 16).Three types of aplasia or hypoplasia can be distin-guished (5). A stenotic IAC with the absence of theVIIIth cranial nerve is a ‘type 1’ malformation. In ‘type2’ malformations, a common vestibulocochlear nerve isfound with hypoplasia or aplasia of its cochlear branch.When this is associated with other inner ear malforma-tions, it is called a ‘type 2A’ malformation; it is called a‘type 2B’ malformation when the inner ear is normal. Inthese patients, the facial nerve often has an aberrantcourse.

Conclusion

Inner ear anomalies are a rare, but they are importantbecause they result in sensorineural hearing loss. Theinner ear dysplasias are best evaluated with a combina-tion of thin section CT to observe the bony labyrinth,and heavily T2-weighted gradient-echo or fast spin-echo3D T2-weighted MRI are the best choices to observe themembranous labyrinth or any abnormalities of thenerves in the internal auditory canal.

References

1. Swartz JD, Harnsberger HR. Imaging of the temporal bone. 3 rd ed.

New York: Thieme Medical Publishers, 1992:240-2822. Casselman JW, Kuhweide R, Ampe W, D’Hont G, Offeciers EF,

Faes WK, Pattyn G. Inner ear malformations in patients with sen-sorineural hearing loss: detection with gradient-echo (3DFT-CISS)MRI. Neuroradiology 1996;38:278-286

3. Casselman JW, Kuhweide R, Deimling M, Ampe W, Dehaene I,Meeus L. Constructive interference in steady state-3DFT MRimaging of the inner ear and cerebellopontine angle. AJNR Am JNeuroradiol 1993;14:47-57

4. Davison HC. Imaging evaluation of sensorineural hearing loss.Seminars in Ultrasound, CT, and MRI 2001;22:229-249

5. Casselman JW, Offeciers EF, Govaerts PJ, Kuhweide R, Geldof H,Somers T, D’Hont G. Aplasia and hypoplasia of the vestibulo-cochlear nerve: Diagnosis with MR imaging. Radiology 1997;202:773-781

6. Jackler RK, Luxford WM, House WF. Congenital malformations ofthe inner ear: a classification based on embryogenesis. Laryngo-scope 1987;97:2-14

7. Urman SM, Talbot JM. Otic capsule dysplasia: clinical and CTfindings. Radiographics 1990;10:823-838

8. Valvassori GE, Clemis JD. The large vestibular aqueduct syn-drome. Laryngoscope 1978;88:723-728

9. Eelkema EA, Curtin HD. Congenital anomalies of the temporalbone. Semin Ultrasound CT MR 1989;10:195-212

10. Okuno T, Takahashi H, Shibahara Y. Temporal bone histopatho-logic findings in Alagille’s syndrome. Arch Otolaryngol Head NeckSurg 1990;116:217-220

11. Davison HC, Harnsberger HR, Lemmerling MM, Mancuso AA,White DK, Tong KA, et al. MR evaluation of vestibulocochlearanomalies associated with large endolymphatic duct and sac.AJNR Am J Neuroradiol 1999;20:1435-1441

12. Yetiser S, Kertmen M, Ozkaptan Y. Vestibular disturbance in pa-tients with large vestibular aqueduct syndrome (LVAS). ActaOtolaryngol 1999;119:641-646

13. Jackler RK, De La Cruz A. The large vestibular aqueduct syn-drome. Laryngoscope 1989;99:1238-1242

14. Mafee MF, Charletta D, Kumar A, Belmont H. Large vestibularaqueduct and congenital sensorineural hearing loss. AJNR Am JNeuroradio 1992;13:805-819

15. Zalzal GH, Tomaski SM, Vezina LG. Enlarged vestibular aqueductand sensorineural hearing loss in childhood. Arch Otolaryngol HeadNeck Surg 1995;121:23-28

16. Shelton C, Luxford WM, Tonokawa LL. The narrow internal audi-tory canal in children: a contraindication to cochlear implants.Otolaryngol Head Neck Surg 1989;100:227-231

Hyun Sook Hong, et al : Inner Ear Anomalies Causing Congenital Sensorineural Hearing Loss

─ 170 ─

J Korean Radiol Soc 2005;52:165-171

─ 171 ─

대한영상의학회지 2005;52:165-171

선천성 감각신경성 난청 환아의 내이이상: CT와 MR 소견1

1순천향대학교부천병원영상의학과2순천향대학교부천병원이비인후과

홍현숙·백상현·차장규·박성진·조준희·박재성·김대호·이혜경·김시찬2

다양한 골성미로의 선천성 이상이 있으며, 이들의 감별진단은 환아의 적절한 치료에 중요하다. 저자들은 선천성 감각

신경성 난청을 보이는 20예 소아의 CT와 MR 소견을 후향적으로 분석하였다. 이중 큰 전정수관과 내 림프낭 8예, 세반

고리관 무형성증 4예, 측 세반고리관-전정형성이상 3예, 큰 전정과 동반된 common cavity 기형 1예, 와우 형성 부전

증 1예, 큰 전정수관과 동반된 몬디니 형성이상 1예, 큰 전정과 동반된 몬디니 이상 1예, 좁은 내이도 1예 등이다. 6예는

일측성이었고, 9예는 동반된 기형를 가지고 있었으며, 9예는 인공 와우 이식을 받았다. CT 스캔은 골 연산을 이용하여

1 mm의 절편두께로 관상면과 횡단면 영상을 얻었다. MR 스캔은 통상적인 뇌영상과 함께 측두골 3D FSE 10 mm 두

께로 얻었다. 저자들은 선천성 감각신경성 난청 환아에서 보이는 내이 병변의 방사선학적 소견을 CT와 MR 소견을 중

심으로 기술하고자 한다.