MAJOR AND MINOR TEMPORAL
BONE ABNORMALITIES
H.RIAHI, B.SOUISSI, I.OMRI, K.BOUAZIZ, O.AZAIZ, M.BEN
MESSAOUD, R.ALLANI, Gh.Bébés, H.MIZOUNI, E.MENIF
Radiology departement. La Rabta university hospital 1007
Jebbari Tunis. Tunisia.
MK 15
INTRODUCTION
•
In contrast to anatomical variants, congenital malformations (CM) –
synonyms are abnormalities or dysplasias – are not only characterized by
a deviation from normal anatomical development, but also from regular
function.
•
They can result from a developmental arrest, irregular embryogenesis or
from both due to spontaneous genetic mutations – this is the case in the
majority of CM of the ear –, genetic transmission, and exogenic factors—
in about 10% of cases.
•
CM of the ear may be found in syndromes—the most known of them are
the Franceschetti (Treacher-Collins), Goldenhar and Klippel-Feil
syndrome.
MATERIALS AND PATIENTS
• Retrospective study during 48 months from July 2008 to June 2011 .
• 50 patients were explored with MDCT including
o
26 women
o
24 men
• All of them consulted for sensorineural hearing loss.
EXPLORATION METHOD
•
CT examinations of the temporal bone are performed at our institution
by using a GE 64 multislices CT without injection of iodinated contrast:
50 patients so 100 ears
•
Acquisition sub-millimeter volume
•
Axial reconstruction: lateral semicircular canal plan
•
Perpendicular coronal reconstructions
•
Oblique reconstructions:
 Reconstructed double-oblique coronal image shows normal anatomy of the long axis of
the incudal body ,

double-oblique orientation of the axial reconstruction plane enables the optimal display of
both the crura and the stapedial footplate at the oval window,

Oblique coronal planes located along the long axes of malleus and incus
• The following structures were evaluated in 100 temporal bones:
 The external auditory canal: stenosis or atresia of the cartilaginous part
of the auditory canal, stenosis or atresia of the bony part,
 The extent of the middle ear cavity, form of tegmen.
 Diminution, dysplasia, rotation, fusion, ectopia, tympanic wall adherence
 Ossicular chain dysplasia, fusion, absence
 Labyrinthine windows open or closed; fistula.
 Cochlear turns, vestibule, semicircular canals, aqueducts.
 The internal auditory canal
 Facial nerve canal: aberration, dehiscence, hypoplasia, thickening,
splitting.
RESULTS
•
External and medial ear deformity:
structure
nombre
External auditory canal
9 (in 9 patients)
Tympanic cavity
3 (3 patients)
Oval/ round windows
24 (15 patients)
malleus
24 (19 patients)
incus
31 (23 patients)
stapes
34 (24patients)
•
Inner ear deformity
structure
nombre
Michel
4(2patients)
Cochlear dysplasia
8 (8 patients)
Vetibule dysplasia
22 (12patients)
Semicircular canal
60 (41 patients)
Vestibular aqueduct
10 (6 patients)
Internal auditory canal
17 (10patients)
EMBRYOLOGY
• In the 3rd week of gestation: formation of the otic placode, an ectodermal
thickening in the neighborhood of the myelencephalon. Invagination of
the otic placode leads to an otic pit and to fusion of their external lips to
the otic vesicle.
•
In the 8th week, the otic capsule is formed, providing the stapes
footplate and the ligament of the oval window.
•
By the 12th week, the labyrinth is well differentiated.
•
The facial nerve grows to reach its destinations between the 4th and 5th
week.
• The middle and external ear develops from the mesodermal
first and second branchial arch and the endodermal first
pharyngeal pouch between the fourth and 30th weeks.
•
Developmental anomalies of the first pharyngeal pouch lead
to disturbances of the eustachian tube and of the tympanic
and mastoid pneumatization.
• Failure of differentiation of the first branchial arch leads to
malformations of the incudomalleal joint, tensor tympani
muscle, and mandible.
• Failure of differentiation of the second branchial arch affects
the facial nerve canal, the stapedius muscle, the lower part
of the ossicular chain, and the styloid process.
•
Disorders of the first and second branchial arches also result in dysplasia
of the auricular cartilage (leading to microtia in the seventh to eighth week,
the earlier the more severe, or to anotia in the seventh week).
•
The external auditory canal arises from deepening of the first branchial
groove in the 9th week. Opening of the bony part of the external auditory
canal starts only in the 30th week, after complete differentiation of the
inner, middle, and outer ear.
•
Failure of the epithelial cells of the first branchial groove to split causes
stenosis or atresia of the external auditory canal, which might be isolated
in an otherwise normal temporal bone.
•
Anomalies of the internal carotid artery are thought to be caused by
maldevelopment of the third branchial arch during the 4th week
DISCUSSION
INNER EAR DEFORMITY
• Most inner ear malformations arise when formation of the membranous
labyrinth is interrupted during the first trimester of pregnancy.
• Only approximately 20% of patients who present with congenital SNHL
have imaging manifestations.
• Malformations of the inner ear may be associated with various other
embryological abnormalities: cervical fistula, renal abnormalities in the
brachio-oto-renal syndrom.
Schematic representation of different stages of developmental arrest in the inner ear
development.
The letters a and b represent sections through the internal auditory canal and round
window, respectively.
A: cochlear aplasia/deformity
Normal cochlea
Michel deformity: complete labyrinthine
aplasia.
Vestibule and semicircular canal
dysplasia
Cochlear aplasia
Enlarged vestibular aqueduct.
Common cavity.
Incomplete partition
Cochlear hypoplasia
MICHEL DEFORMITY
• Complete absence of all cochlear and vestibular elements.
• Rarely unilateral.
• Associated lesions:
 Aberrant facial nerve
 Absent stapes
 Abnormality of the skull base
 Aberrant internal carotid
 stapedial artery
COCHLEAR APLASIA
• This is seen as dense otic bone
on the anterior part of the IAC.
•
Because of the absence of the
cochlea, the course of the
labyrinthine segment of the facial
canal is more anterior at the usual
location of the cochlea.
• It is important to differentiate this
malformation from cochlear
ossification in which the basal turn
of the cochlea produces the
characteristic bulging in the
middle ear(the promontory).
COMMON CAVITY.
• cochlea and vestibule form a
common cavity, which
represents both of these
structures without any
differentiation.
• Usually, the internal auditory
canal enters the common cavity
at its center.
INCOMPLETE PARTITION
• Cystic dilated vestibule accompanied
the cystic, empty cochlea.
• the dimensions of the cochlea and
vestibule are normal but the internal
architecture is missing.
• There is no modiolus in the cochlea,
giving it the shape of an empty cystic
structure.
• Usually, the cribriform area between the
cochlea and the IAC is also defective.
COCHLEAR HYPOPLASIA
•
Cochlear and vestibular structures are
separate from each other.
•
In hypoplasia the cochlea is smaller than
normal.
•
Only the basal turn is developed, the
other turns form one commun cavity.
•
The accompanying vestibular
malformation is usually absence or
hypoplasia.
VESTIBULE AND SEMICIRCULAR
CANAL DYSPLASIA
• SCC malformations also frequently
occur in association with other inner
ear anomalies.
• The SCCs begin as disk-shaped
evaginations arising from the
vestibular appendage in the 6th
gestational week.
• The superior SCC is the first to form, followed
by the posterior and then the lateral SCC.
Therefore, superior and posterior SCC
anomalies are almost invariably associated
with anomalies of the lateral SCC, whereas
abnormalities of the lateral SCC can occur in
isolation.
• On axial CT images, subtle SCC
abnormalities may be indicated by a small or
enlarged lateral SCC bony island. Normally,
the transverse diameter of this bony island
measures between 2.6 and 4.8 mm
LARGE VESTIBULE
• There appears to be a reciprocal
relationship between the size of semi
circulars canals particularly the lateral
canal and the size of the vestibule.
• An enlarged vestibule is associated with
underdeveloped lateral semi-circular
canal
ENLARGED VESTIBULAR AQUEDUCT
•
Vestibular aqueduct enlargement (also referred to
as enlarged vestibular aqueduct syndrome) is the
single most common inner ear anomaly seen in
individuals with SNHL.
•
It is frequently seen in association with other inner
ear anomalies( vestibular enlargement, and SCC
dysplasias)
•
On CT, vestibular aqueduct enlargement is
diagnosed when the aqueduct is 1.5 mm in width
(roughly the diameter of the simultaneously
visualized posterior SCC) at the midpoint between
the common crus and its external aperture.
•
MR imaging additionally demonstrates
enlargement of the endolymphatic duct and sac.
SMALL INTERNAL AUDITORY CANAL
• This deformity is characterized by
a decrease in the diameter of the
IAC
• Presumably, this hypoplastic
changes are secondary to
hypooplasia or aplasia of the
cochlear nerve
EXTERNAL AND MIDDLE EAR
DEFORMITY
• Many classifications
 Moderate malformation
 Severe malformation
• Elementary lesions:
 External acoustic canal
 Middle ear
 ossicular chain
EXTERNAL AUDITORY CANAL
•
Failures of the canalisation result in EAC
malformations including membranous
and/or bony atresia.
•
The classification of malformations of the
EAC according to Weerda
 EAC stenosis type A: a marked narrowing
of the EAC with an intact skin layer.
 EAC stenosis type B: a partial
development of the EAC with an atresia
plate at the medial part.
 Type C: complete bony EAC atresia.
MIDDLE EAR
•
Middle ear malformations can affect the normal
development of the tympanic cavity as well as ossicles
and form a continuum with varying degrees of
involvement.
•
This is linked with a change in configuration or size of
middle ear spaces:
 Mastoid pneumatization may be reduced or absent.
 Tympanic cavity: may be
o
hypoplasia: the cavity is shorter and or smaller than
normal;
o split-like deformed: then often opacified and filled with
non-resorbed embryonic or fibrosing tissue
o
aplasia:absence
o
extracavitation: an additional cavity on a wrong place
•
There may be abnormalities of the oval window and,
rarely, of the round window.
OSSICULAR CHAIN
• Malleus:
 fused malleus and incus
 fixation of malleus and/or incus on the
tympanic wall
 aplasia of the head of the malleus
• Incus:
 No or hypoplasic incus long
process
 Incus fused to medial attic wall
 No connexion with malleus
 incus long process fused to
promontrium
 Fused incus and stapes
• Stapes:
 Stapes without anterior crus or stapes
suprastructure
 Stapes with monopolar crus
 Stapes footplate fixation
 No stapes footplate
CONCLUSION
• Well-established temporal bone abnormalities such as cochlear and
vestibular abnormalities and a grossly enlarged vestibular aqueduct are
significantly found in patients with sensorineural hearing loss.
•
CT and MRI allow labelling from isolated malformations or from simple
morphological considerations to guide to an abnormal type geyser, a
syndrome branchio-oto-renal or load before any result would then
specify the genetic disorder in question.