Inner Ear Malformations: a Practical Diagnostic Approachଝ

Home , Modiolus (cochlea)

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Radiología. 2017;59(4):297---305

www.elsevier.es/rx

RADIOLOGY THROUGH IMAGES

Inner ear malformations: A practical diagnostic approachଝ

a,∗ b a a a

M. Mazón , E. Pont , A. Montoya-Filardi , J. Carreres-Polo , F. Más-Estellés

Área Clínica de Imagen Médica, Hospital Universitario y Politécnico La Fe, Valencia, Spain

Servicio de Otorrinolaringología, Hospital General de Onteniente, Valencia, Spain

Received 20 July 2016; accepted 27 September 2016

KEYWORDS Abstract Pediatric sensorineural hearing loss is a major cause of disability; although inner ear

Diagnostic imaging; malformations account for only 20---40% of all cases, recognition and characterization will be

Ear inner; vital for the proper management of these patients. In this article relevant anatomy and devel-

Abnormalities; opment of inner ear are surveyed. The role of neuroimaging in pediatric sensorineural hearing

Cochlear displasia; loss and cochlear preimplantation study are assessed. The need for a universal system of classi-

Cochlear aplasia; ﬁcation of inner ear malformations with therapeutic and prognostic implications is highlighted.

Incomplete partition And ﬁnally, the radiological ﬁndings of each type of malformation are concisely described and

depicted. Computed tomography and magnetic resonance imaging play a crucial role in the char-

acterization of inner ear malformations and allow the assessment of the anatomical structures

that enable the selection of appropriate treatment and surgical approach.

PALABRAS CLAVE

Malformaciones del oído interno: una aproximación diagnóstica práctica

Imagen diagnóstica;

Oído interno; Resumen La hipoacusia neurosensorial pediátrica es una causa mayor de discapacidad. Pese a

Anormalidades; que solo en el 20-40% de los casos se identiﬁca una malformación del oído interno, su detección

Displasia coclear; es de vital importancia para el tratamiento de estos pacientes. En este artículo se repasan la

Aplasia coclear; anatomía y la embriogénesis del oído interno. Se valora el papel de la neuroimagen en la hipoa-

Partición incompleta cusia neurosensorial pediátrica y en el estudio preimplante coclear. Se destaca la necesidad de

la utilización de un sistema universal de clasiﬁcación de las malformaciones del oído interno con

ଝ

Please cite this article as: Mazón M, Pont E, Montoya-Filardi A, Carreres-Polo J, Más-Estellés F. Malformaciones del oído interno: una

aproximación diagnóstica práctica. Radiología. 2017;59:297---305. ∗

Corresponding author.

E-mail address: [email protected] (M. Mazón).

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298 M. Mazón et al.

implicaciones pronósticas y terapéuticas. Por último, se describen e ilustran de forma concisa

los hallazgos radiológicos clave de cada tipo de malformación. La tomografía computarizada y

la resonancia magnética desempenan˜ un papel crucial en la caracterización de las malforma-

ciones del oído interno y permiten la valoración de las estructuras anatómicas que posibilitan

la selección del tratamiento y del abordaje quirúrgico idóneos.

Introduction Through the cochlear opening the cochlea meets the fun-

dus of the internal acoustic canal (IAC) the cochlear nerve

passes through. The vestibular system is made up of the

Sensorineural hearing loss in children is a major cause of

vestibule and three semicircular ducts: superior, lateral, and

disability. Its early diagnosis is very important since delayed

posterior.

diagnoses may affect the development of language, the

Both the duct and the endolymphatic sac are contained

academic skills and social and emotional development. It

by the vestibular aqueduct reaching out from the labyrinth

can be due to congenital or acquired anomalies; at least

toward the posterior fossa epidural space.

half of them have a genetic origin and among the acquired

The IAC runs through the petrous part of the temporal

ones the infection due to cytomegalovirus is the most com-

1 bone and communicates the cerebellopontine angle cistern

mon cause. The prevalence of detectable cochleovestibular

2 with the labyrinth through which the cranial nerves VII and

malformations is around 20---40%.

VIII pass. In an oblique sagittal plane perpendicular to the

The cochlear implant is the standard therapeutic

IAC we can see the facial nerve in the anterior-superior

proceeding of mild to profound sensorineural hearing loss

3 quadrant, the cochlear nerve in the anterior-inferior quad-

in children. Previously inner ear (IE) malformations were

rant and the upper and lower vestibular nerves in the

one counter indication for cochlear implants but advances

posterior quadrants.

in surgical techniques and cochlear devices have made it

The IE stems from the otic placode that starts develop-

possible to implant cochleas with malformations.

ing during the 3rd week of pregnancy. The development of

Image modalities are crucial when it comes to doing

the cochlea is completed in the 8th week of pregnancy, the

preoperative assessments of inner ear malformations since

vestibule in the 11th week and semicircular ducts between

they allow us to detect and evaluate the cochlear nerve

the 19th and 22nd weeks of pregnancy. The ﬁrst semicircular

and identify any anatomic variants and all potential surgical

complications.1 duct to develop is the superior one followed by the posterior

one and the last one to develop is the lateral one.

There are several categorization schemes for IE malfor-

mations and yet despite the fact that no scheme is perfect

we should make the effort of trying to adopt a universal

The role of neuroimaging in inner ear

system that would allow us to share our results with the

scientiﬁc community. malformations

In this paper we will take a brief look into the anatomy

and embryogenesis of the IE. We will also be evaluating the Most candidates for a cochlear implant do not show anoma-

role of neuroimages in pediatric sensorineural hearing loss lies in their temporal bone that can be identiﬁed through

and in the cochlear preimplant study. We will be paying spe- images, but if they show such anomalies ﬁnding them is very

cial attention to the use of a somehow universal system to important. Both computed tomography (CT) and magnetic

categorize IE malformations with therapeutic and prognostic resonance imaging (MRI) give us an excellent representa-

implications. Finally we will be describing the most widely tion of IE malformations and they are used in the systematic

accepted categorization while illustrating and detailing in practice of the study of pediatric sensorineural hearing loss

a concise way the key radiologic ﬁndings of each type of and cochlear pre-implants. Because of their complementary

malformation. role the use of both image modalities is recommended since

the rate of malformation detection increases dramatically.

CT allows us to detect bone malformations, also the facial

Anatomy and embryology of inner ear nerve possible aberrant trajectory (more common in this

population ), vascular structure malformations and assess

The IE is made up of the membranous labyrinth that in coexisting anomalies of both the inner and middle ears.

turn surrounds the osseous labyrinth. The cochlea-organ When it comes to the MRI it allows us to assess ﬂuid-ﬁlled

responsible for hearing is a conical structure consisting of spaces of the IE and assess the cranial nerve VII and any other

a duct that makes between 2.5 and 2.75 turns around a possible intracranial anomalies.

central core called modiolus (Fig. 1). From the modiolus Combined they provide the surgeon with the necessary

a thinned-osseous spiral layer reaches out to divide the presurgical information that will allow him/her to make a

duct into vestibular duct (upper) and tympanic duct (lower). therapeutic decision, give advise for parents and give the

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Inner ear malformations: A practical diagnostic approach 299

Figure 1 Chart showing the EI made up of the cochlea (co), the vestibule (v) and the semicircular ducts (csc). The modiolus (m)

is the base of the cochlea at the fundus of the internal acoustic canal (IAC). The cochlear coils are separated by the interscalar

septum (ti); the coil is split into vestibular duct (rv) and tympanic duct (rt) by the spiral lamina (le) that stems from the modiolus.

The vestibular aqueduct (av) stems from the vestibule toward the epidural espace of the posterior fossa with a trajectory across the

petrous part of the temporal bone and perpendicular to the IAC. (B) Representation of anatomical structures in a transverse image

using computed tomography in bone window. (C) Representation of anatomical structures in a transverse image using a T2-weighted,

echo-gradient, high-resolution, steady-state MRI sequence. (D) Oblique, sagittal reconstruction perpendicular to the IAC of the MRI

sequence showing the facial nerve (nf) in the superior-anterior quadrant, the cochlear nerve (nc) in the inferior-anterior quadrant,

the superior vestibular nerve (nvs) in the superior-posterior quadrant, ant the inferior vestibular nerve (nvi) in the inferior-posterior

quadrant. In this image the anterior part is marked with an A and the posterior one with a P.

most likely prognosis for the cochlear implant, choose the surgical complications we will ﬁnd and worse the outcome

2,3,5,6

surgical approach and the appropriate implants and warn of cochlear implant will be.

about anatomic variants and any other possible surgical In our radiologic report on top of classifying mal-

complications. formations we also give detailed information on three

anatomic structures involved in the cochlear implant:

cochlear lumen---where the electroded will be placed: the

Classiﬁcation

modiolus---target of electrostimulation; and the cochlear

nerve---the route through which the stimulus travels.

There are many classiﬁcations when it comes to IE malforma-

Now let us take a look at the different types of malfor-

tions and it is precisely the absence of a common language

mations we can see (table available online).

that makes understanding hard for the scientiﬁc commu-

nity. We need a universal classiﬁcation system that allows

us to determine the link among the different types of mal- Complete labyrinthine aplasia

formations and clinical prognosis. The most widely accepted

categorization is Sennaroglu classiﬁcation ---the classiﬁca- Also known as Michel aplasia it is the result of the interrup-

tion this paper is based on. It is based on embryogenesis. tion of the otic placode development before the 3rd week

Every malformation is the consequence of an interruption in of pregnancy. It amounts to 1% of IE malformations only. It

development at one time or another. Generally speaking it counter indicates cochlear implantation and the best ther-

is useful and the more serious the malformation, the more apeutic option is the brainstem implant.

Figure 2 Complete labyrinthine aplasia. (A) Transverse image using computed tomography in bone window with identiﬁable total

absence of inner ear elements (asterisk). We can see hypoplasia in the petrous part of the temporal bone (white arrow), the atresic

internal acoustic canal (IAC) with a reduced caliber (black arrow), and the ﬂattening of the inner ear medial side (arrowhead). (B)

Transverse image using T2-weighted, echo-gradient, steady-state MRI sequence where the aforementioned ﬁndings can be seen as

well as the cranial pairs; in this case there is an absolute deﬁcit of the vestibulocochlear nerve and only the facial nerve (arrowhead)

can be seen in the cerebellopontine angle cistern and the IAC.

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300 M. Mazón et al.

Figure 3 Cochlear aplasia. (A) The chart shows the total absence of the cochlea (asterisk) and the normalcy of the inner ear

remaining structures. (B and C) Transverse image using computed tomography sequence in bone window---superior and inferior,

respectively, where we can easily identify the absence of the cochlea (black asterisk). The vestibule is dysplasic (black arrow) and

the facial nerve shows an aberrant itinerary with a widening of its labyrinthic part (white arrow). In C we can see the ﬂattening

of the inner ear medial side (arrowhead)---with this ﬁnding we can distinguish this malformation from labyrinthitis ossiﬁcans. This

patient also showed chronic otitis media and inﬂammatory erosion of the ossicular chain; the occupation of the middle ear and

mastoid air cells by a soft dentistry tissue/material and almost total erosion of the ossicular chain (white asterisk).

It is characterized by a total absence of IE struc-

tures (Fig. 2). The IAC is atresic, there is aplasia of the

cochleovestibular nerve and the facial nerve trajectory is

aberrant. It is associated with multiple anomalies of the

temporal lobe among which the following ones are the most

common of all: petrous apex hypoplasia, absence of round

and oval windows and ﬂattening of the middle ear medial

4,9

wall due to absence of promotorium.

Cochlear aplasia

It is due to developmental interruption at the end of

the 3rd week of pregnancy and it amounts to 3% of all

IE malformations. It is a counterindication for cochlear

implantation.

The cochlea is absent and the vestibular system can be

normal, dysplasic, distinguishable from the cochlea due to

its posterior location with respect to the IAC (Fig. 3). The

labyrinthic segment of the facial nerve has an aberrant tra-

Figure 4 Online Labyrinthitis ossiﬁcans Transverse image

jectory and the inner ear medial wall is ﬂattened.

using computed tomography sequence showing an almost com-

plete cochlear ossiﬁcation (black arrow). The inner ear medial

side is not ﬂattened and the promontorium can be easily iden-

We should remember that: in labyrinthine apla- tiﬁed (white arrow) --- ﬁndings that will allow us to distinguish

sia and cochlear aplasia there is ﬂattening of the it from labyrinthine and cochlear aplasias.

inner ear medial wall---useful ﬁnding to distinguish them

from labyrinthitis ossiﬁcans (Fig. 4 available online).

architecture (Fig. 5). There is a total absence of modio-

This differentiation is clinically relevant since in the

lus and a large communication between the cavity and the

labyrinthitis ossiﬁcans the cochear implant is possible 12

IAC. Semicircular ducts are usually dysplasic though there

hard to accomplish. 4

are times that they may look normal.

Incomplete partition type I

Common cavity Also known as cystic cochleovestibular malformation it is

due to developmental interruption during the 5th week of

It is the result of developmental interruption during pregnancy.

the 4th week of pregnancy and amounts to 25% of all The cochlea shows a total absence of the modiolus

4,10

malformations. Cochlear implant is possible though hard and cystic appearance without internal architecture; the

to accomplish and the rate of complications is higher. vestibule is dilated. The labyrinth as a whole has the appear-

It is characterized to be the conﬂuence of the cochlea ance of the ﬁgure eight (Fig. 6). In this malformation we

and the vestibule in one only cystic cavity without internal can see the cochlea and the vestibule which in turn allows

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Inner ear malformations: A practical diagnostic approach 301

Figure 5 Common cavity. (A) The chart shows common cystic cavity without internal architecture made up by rudimentary

cochlea and vestibule. (B and C) Transverse image and coronal multiplanar reconstruction using computed tomography in window

bone, respectively showing the common cavity (white arrows) and slightly dysplasic, widened and short semicircular ducts (black

arrows). The fundus of the IAC showing cribiform plate deﬁcits (arrowhead) enters the center of the common cavity; ﬁnding that

allows us to distinguish this malformation from cochlear aplasia with dysplasic dilated vestibule in which the fundus of the IAC

location is anterior to the cavity that is more posterior in the normal situation of the vestibule.

us to distinguish it from the common cavity. The cribiform Incomplete partition type III

region located between the cochlea and the IAC is usually

11,13

defective. It is a recessive genetically inherited disease linked to

chromosome X and it is not due to the developmental

interruption of the otic placode. It usually affects males and

Incomplete partition type II

mixed hearing loss of rapid progression.

There is a total absence of the modiolus though the inter-

It is due to developmental interruption during the 7th week

scalar septum is present (Fig. 8). The cochlea is located

of pregnancy and it is the most common dysplasia of all

4 laterally to the IAC that is in turn widened and both widely

(present in 50% of all malformations).

communicated due to a complete deﬁcit of the cribose

It shows fusion of the middle and apical turns and a cys-

layer.15,16

tic appearance due to a defect in the apical segment of the

modiolus, the interscalar septum and the osseus spiral lam-

ina (Fig. 7). The modiolus basal coil and the basal segment

look normal.

It is usually associated with an enlarged vestibular aque- We should remember that: malformations with crib-

duct (due to duct and endolymphatic sac dilation) and with iform plate deﬁcits and a wide communication between

a minimal vestibular dilation which makes up the Mondini the IAC and the cochlea (common cavity, incom-

deformity triad. plete partitions types I and III) predispose to a higher

risk of recurrent meningitis, perilymphatic ﬁstula and

complications during surgery.

We should remember that: it is not right to deﬁne

incomplete partition as a cochlea consisting of 1.5 turns

since that is reserved for cochlear hypoplasia.

Figure 6 Incomplete partition type I. (A) The chart shows the cochlea with a total absence of modiolus and interscalar septum

without internal architecture. The vestibule is dysplasic, slightly dilated and the labyrinth as a whole shows the shape of ﬁgure eight.

(B) Transverses image using computed tomography in bone window. (C) Maximum intensity projection reconstruction of transverse

image using T2-weighted, steady-state, echo gradient MRI sequence. In B and C we can see the following ﬁndings: cochlea without

internal architecture (white arrow) and slightly dilated vestibule (black arrow) making up an eight shaped-labyrinth. Cribiform

plate deﬁcit (arrowhead) with wide communication between the IAC and the cochlea can be identiﬁed here. In C the cochlear nerve

deﬁcit can be seen (black asterisk in the theoretical location of the nerve). The patient shows chronic otitis media; in B we can see

the occupation of the middle ear (white asterisk).

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302 M. Mazón et al.

Figure 7 Incomplete partition type II. (A) The chart shows the conﬂuence of the middle and apical cochlear coil due to the absence

of the apical part of the modiolus and interscalar septum that gives the apex a cystic appearance (arrows). The vestibular aqueduct

is usually widened due to duct and endolymphatic sac dilation (arrowhead). (B) Transverse image using computed tomography (CT)

in bone window. (C) Transverse image using T2-weighted, steady-state, echo-gradient MRI sequence. In B and C we can identify the

following ﬁndings: cystic apex due to fusion of middle and apical coils (white arrows), and dilated vestibular aqueduct in the CT,

and duct and endolymphatic sac dilation in the MRI (arrowhead). (D) Oblique sagittal reconstruction perpendicular to the IAC of

the T2-weighted, steady-state, echo-gradient sequence where a normal size cochlear nerve (arrow) can be seen. The upper part is

marked with an A and the posterior one with a P. The patient showed chronic otitis media; in B and C we can see the occupation of

the middle ear (asterisk).

Figure 8 Incomplete partition type III. (A) The chart shows rotated cochlea located directly in the lateral edge of the IAC with a

total absence of the modiolus but with the interscalar septum. There is cribiform plate deﬁcit with wide communication between the

IAC and the cochlea. (B) Transverse image using computed tomography in bone window. (C) Transverse image using T2-weighted,

steady-state, echo-gradient MRI sequence. In B and C we can see rotation of the cochlea (the curved arrow shows the rotation

direction) directly lateral to the IAC showing a total absence of the modiolus (asterisk) but the interscalar septum (arrowhead). In

C we can see a cochlear nerve of normal thickness (arrow).

Cochlear hypoplasia communication with the IAC that predisposes to a higher

risk of complications during surgery. The vestibular aque-

It is due to developmental interruption during the 6th week duct is usually widened and the vestibule is slightly

4 7

of pregnancy. The dimensions of the cochlea are smaller dilated.

but there is a well-established differentiation between Type III, cochlea with less than two turns: the cochlea

the cochlea and the vestibule. When in lack of expe- shows less than two turns, the modiolus is smaller and

rience measurements should be taken to facilitate its the interscalar septum is shorter but both its internal and

detection. internal architectures are normal. The vestibule and the

It is a generic term and three subtypes should be taken semicircular ducts are usually hypoplasic.

into consideration here (Fig. 9):

Type I, ‘‘yolk sac’’ of the cochlea: the cochlea is a small Widened vestibular aqueduct syndrome

excrescence stemming from the vestibule with no internal

architecture and a total absence of modiolus and inter- Its etiology is controversial; it could be due to postna-

scalar septum. tal developmental disorders. It consists of an isolated

Type II, cystic hypoplasic cochlea: the cochlea shows vestibular aqueduct widening due to the duct and endolym-

reduced dimensions, no mediolus or interscalar sep- phatic sac abnormal developments being the remainder of

tum but its external structure is normal. It shows wide the labyrinth normal (Fig. 10). The aqueduct is said to be

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Inner ear malformations: A practical diagnostic approach 303

Figure 9 Cochlear hypoplasia. (A) The chart shows the existing three types of cochlear hypoplasia: type I ‘‘yolk sac’’, like a small

excrescence stemming from the vestibule; type II, cystic hypoplasic of normal external architecture but small dimensions and no

internal architecture due to the absence of modiolus and interscalar septum; type III, less turns with normal external and internal

architecture but shorter modiolus and interscalar septum which conditions the cochlea with less than two turns. (B) Transverse

image using computed tomography (CT) in bone window showing hypoplasic ‘‘yolk sac’’-like cochlea stemming from the vestibule

like a small excrescence (type I). (C) Transverse image using CT in bone window showing one hypoplasic cystic cochlea of normal

external architecture but reduced dimensions and no internal architecture (type II). (D) Transverse image using CT in window bone

showing one hypoplasic cochlea with less than two turns (type III).

Figure 10 Dilated vestibular aqueduct syndrome. (A) Transverse image using computed tomography in bone window showing

vestibular aqueduct widening (white arrow); it is useful to use the caliber of the superior semicircular duct as a reference of

the upper threshold of normalcy (arrowhead). (B) Transverse image using T2-weighted, steady-state, echo-gradient MRI sequence

showing duct and endolymphatic dilation (white arrow) and the posterior semicircular duct as a reference (arrowhead). Both the

cochlea and the rest of the inner ear are normal (black arrow in A and B).

widened when its caliber is larger than 0.8 mm in its central with a strong association with other IE malformations and

◦ 19

point in an oblique plane at 45 (plane of Pöschl). certain syndromes. The vestibule and the lateral semicircu-

lar duct dysplasia is one of the strongest ones and consists

of a short and wide lateral semicircular duct fused or sepa-

Vestibular system malformations

rated through a small bony islet to the vestibule of globular

appearance (Fig. 11). There is a strong correlation between

It is due to developmental disorders between the 6th and 20

the aplasia of semicircular ducts and CHARGE syndrome

22nd weeks of pregnancy. In isolation it is not relevant for

(Fig. 12).

the cochlear pre-implant study; its importance has to do

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304 M. Mazón et al.

malformation and illustrate and give precise details on key

radiological ﬁndings.

Ethical responsibilities

Protection of people and animals. The authors declare that

the proceedings followed fully abide by the ethical rules and

regulations from the human experimentation committee and

are in full compliance with the World Health Organization

(WHO) and the Declaration of Helsinki.

Conﬁdentiality of data. The authors conﬁrm that they have

followed their centers protocols on the publication and dis-

closure of data from patients.

Right to privacy and informed consent. The authors con-

ﬁrm that they have received written informed consent from

the patients and/or individuals referred to in this paper. This

Figure 11 Vestibular malformation. Transverse image using

manuscript belongs to the corresponding author.

MRI in bone window showing the vestibule of globular appear-

ance fused into the lateral semicircular duct (arrow).

Authors

1. Manager of the integrity of the study: MM and EP.

2. Study Idea: MM, EP, AMF, JCP and FME.

3. Study Design: MM and EP.

4. Data Mining: MM, EP, AMF, JCP and FME.

5. Data Analysis and Interpretation: N/A.

6. Statistical Analysis: N/A.

7. Reference: MM, EP, AMF, JCP and FME.

8. Writing: MM and EP.

9. Critical review of the manuscript with intellectually rel-

evant remarks: MM, EP, AMF, JCP and FME.

10. Approval of ﬁnal version: MM, EP, AMF, JCP and FME.

Conﬂicts of interests

The authors declare no conﬂict of interests associated with

this article whatsoever.

Figure 12 Vestibular malformation. Transverse image using

Appendix A. Supplementary data

MRI in bone window in patient with CHARGE syndrome showing

vestibular hypoplasia (black arrow) and semicircular ducts apla-

sia (asterisk). It shows cochlear hypoplasia type II (arrowhead) Supplementary material related to this article can be found,

and fused ossicular chain dysplasia (white arrow). The CHARGE in the online version, at http://dx.doi.org/10.1016/j.rx.

syndrome is a genetic poliformative disease whose abbrevia- 2016.09.009.

tion stands for Coloboma of the eye, heart defects, atresia of

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