Download Osseous structures in the middle ear cavity(MEC): Are they too many

Osseous structures in the middle ear cavity(MEC): Are they
too many or are they too few?
Poster No.:
C-2286
Congress:
ECR 2013
Type:
Educational Exhibit
Authors:
P. Mundada, B. S. Purohit, T. Tiong Yong; Singapore/SG
Keywords:
Computer Applications-3D, CT, Ear / Nose / Throat, Calcifications /
Calculi, Inflammation, Infection
DOI:
10.1594/ecr2013/C-2286
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Learning objectives
1. To acquaint the reader with normal anatomy and normal appearance of ossicular chain
and its ligaments on CT.
2. To acquaint readers with various common and uncommon conditions which are seen
as "too many" or "too few' osseus structures within MEC.
Background
CT is the modality of choice for temporal bone evaluation in cases of conductive hearing
loss(CHL) and mixed hearing loss(MHL). In these clinical scenarios, CT scan of temporal
bone is performed to demonstrate integrity of ossicular chain and also to look for other
causes which may present as CHL and MHL.
In few instances, while evaluating the ossicular chain integrity, one or more components
of ossicular chain may be found missing ("too few") or one may find extra osseous
structure/s ("too many") within MEC which can cause fixation of ossicle/s.
Various conditions which may present as "too few" osseous structures within MEC are:
1. Dysplasia of ossicle/s
2. Erosion of ossicle/s secondary to cholesteatoma
3. Erosion of ossicle/s secondary to infection.
4. Traumatic destruction or displacement of ossicle
5. Post-surgical.
Various conditions which may present as "too many" osseous structures within MEC are:
1. Fibro-osseous tympanosclerosis
2. Congenital bony bar
3. Ossification of suspensory ligament/s
4. Ossification of stapedial tendon
5. Bone forming neoplasm in MEC
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6. Rarely a large otosclerotic plaque may protrude in MEC.
Imaging findings OR Procedure details
Brief normal anatomy of ossicles, suspensory ligaemnts and tendons in MEC (1*):
Anatomy of the ossicular chain is excellently demonstrated on CT. Multi planar
reconstructions and 3-D images further improve delineation of smaller parts of ossicles.
Use of various signs like '2 parallel lines sign' and '2 dots sign', helps in detecting subtle
discontinuity of ossicluar chain. A good acquaintance with the normal appearance of
various processes of ossicles and also that of ossicular joints will help in detecting
presence of small erosion or ossicular dysplasia and abnormal ossification.
Knowledge of the normal rate of visibility and range of variation in the appearance of
the ligaments and tendons of the middle ear may be helpful in examining patients with
CHL and MHL.
The anterior, lateral, and superior malleal ligaments and the posterior incudal ligament
are suspensory ligaments which connect the malleus and incus to the tympanic wall. The
malleus and incus are connected by the incudomalleal joint, which has a capsule as well
as medial and lateral incudomalleal ligaments. The incudal lenticular process and the
head of the stapes are connected at the incudostapedial joint.
Of these, the lateral malleal ligament is most consistently seen in its entirety. Visibility of
other ligaments in entirety is variable. The stapedious tendon when seen "very well" is
considered abnormal. Ligaments that are seen "too well" on high-resolution CT scans,
might, in the proper clinical setting, be a sign of abnormal change.
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Fig. 1: Icecream cone sign. Head of malleus(arrow). Body of incus(arrow head).
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
Page 4 of 30
Fig. 3: 'Two parallel lines sign' (arrow). Anterior line is handle of malleus. Posterior line
is long process of incus.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
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Fig. 4: 'Two dots sign'(arrow). Medial dot is head of stapes. Lateral dot is lenticular
process of incus. Manubrium of malleus(arrow head)is seen anteriorly.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
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Fig. 2: Normal L-appearance of incudo-stapideal joint on coronal image.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
Page 7 of 30
Fig. 5: Superior malleal ligament (horizontal arrow). Lateral malleal ligament( vertical
arrow). Tendon of tensor tympani (arrow head).
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/
SG
Page 8 of 30
Fig. 6: Anterior malleal ligament.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/
SG
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Fig. 7: Medial posterior incudal ligament (arrow). Its lateral counterpart is almost never
seen on imaging.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/
SG
Page 10 of 30
Fig. 8: Expected location of stapedious tendon (arrow).
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
Various conditions which may present as "too few" osseous structures within MEC
are:
1. Ossicular dysplasia: Ossicular dysplasia may be associated with various syndromes
st
nd
or may present in isolation as part of 1 and 2 branchial arch dysplasia. They are
classified into four groups (2*) and the classification helps to predict the surgical outcome.
1.
2.
3.
4.
Class I Stapes fixation only
Class II Stapes fixation with other ossicular malformation
Class III ossicular malformation with mobile stapes
Class IV aplasia or dysplasia of the oval or round window
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Fig. 9: 2nd branchial arch dysplasia. Absent stapes superstructure and long
process of incus. "two dots sign' and 'tow parrallel lines sign' are absent. Malleus is
normal(arrow).
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
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Fig. 10: Absent stapes superstructure and long process of incus(arrow). Stapes foot
plate is normal (arrow head).
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
2. Erosion of ossicle/s secondary to cholesteatoma:
Pars flaccida and pars tensa cholesteatoma are associated with retraction of tympanic
membrane, chronic inflammatory soft tissue in MEC and erosions of ossicles and that of
bony walls of MEC. Large erosions along the posterior wall of MEC may lead to auto mastoidectomy.
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Fig. 11: Clinically known case of cholesteatoma. Incus is completely eroded (arrow).
Absent 'ice cream cone". Malleus is intact (arrow head). Soft tissue in MEC. Temporal
bone is sclerotic.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
Page 14 of 30
Fig. 12: Clinically known case of cholesteatoma. Incus and stapes super structure are
completely eroded. Erosions of bony walls of MEC (arrow head). Soft tissue in MEC.
Temporal bone is sclerotic.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
3. Erosion of ossicle/s secondary to infection:
Chronic infections of middle ear cavity are rare in adults as compared to those in children.
Unsafe type of chronic suppurative otitis media (CSOM) are known be associated with
erosions of bony walls of MEC and that of ossicles. Cholesteatoma may coexist with
CSOM.
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Fig. 13: CSOM in an immunocompromised young adult. Incus and stapes are
destroyed. Malleus is also eroded (arrow). Tegmen tympanum is eroded (arrow head).
On imaging it is indistinguishable from cholesteatoma.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
4. Traumatic destruction or displacement of ossicle:
Fracture of temporal bone or penetrating injury to middle ear cavity can dislodge or
destroy ossicles.
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Fig. 14: History of penetrating injury to middle ear. Absent 'two dots sign".
Malleus(arrow head) and incus(arrow)are seen. Stapes is missing.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/
SG
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Fig. 15: Stapes is displaced within the vestibule (arrow). Small speck of air is
suggestive of pneumolabyrinth.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
5. Post surgical:
Partial or complete surgical removal of one or more ossicles and also repositioning of
ossicles may be done to restore the continuity of the ossicular chain. Incus is most
commonly excised or repositioned ossicle.
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Fig. 16: Post canal wall down mastoidectomy and ossiculoplasty. 'Two parrale lines'
sign is absent.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
Page 19 of 30
Fig. 17: Post canal wall down mastoidectomy and ossiculoplasty. Incus is resected
and a bony bridge( arrow)is seen between the stapes head and the tympanic
membrane.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
Various conditions which may present as "too many" osseous structures within
MEC are:
1. Fibro-osseous tympanosclerosis (3*):
Postinflammatory ossicular fixation shows three pathologic forms: fibrous tissue fixation
(chronic adhesive otitis media), hyalinization of collagen (tympanosclerosis), and new
bone formation (fibro-osseous sclerosis).
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Tympanosclerosis appears as unifocal or multifocal punctate or weblike calcifications in
the middle ear cavity or on the tympanic membrane.
New bone formation (fibro-osseous sclerosis) is usually seen in the attic and is the
least common manifestation. Thick bony webs or generalized bony encasement may be
present at CT.
Fig. 18: Background changes of chronic otitis media. New bone formation (fibroosseous fixation) is seen in the attic (arrow).
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
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Fig. 19: Background changes of chronic otitis media. New bone formation (fibroosseous fixation) is seen in the attic (arrow). Head of malleus (arrow head).
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
2. Congenital bony bar in the MEC (4*):
Congenital bony bar in the MEC is a rare condition which causes fixation of ossicle
to tympanic cavity wall and results in CHL. It is differntiated from suspensory ligament
ossification is on the basis of its location. Lack of background chronic otitis media
differentiates it from tympanosclerosis.
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Fig. 20: A congenital bony bar (arrow) is fixing the body of incus to the facial nerve
canal. Location of bony bar excluded the possibility of ligament ossification. Lack of
background chronic otitis media excludes tympanosclerosis.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
Page 23 of 30
Fig. 21: A congenital bony bar (arrow) is fixing the handle of malleus (arrow head) to
the posterior wall of MEC. This condition is also known as 'Malleus bar". Its location
along the expected course of chorda tympani nerve makes it indistinguishable from
similar looking ossification of chorda tympani sheath, although later is an extremely
uncommon condition. Location of bony bar excluded the possibility of ligament
ossification. Lack of background chronic otitis media excludes tympanosclerosis.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
3. Ossification / calcification of suspensory ligaments:
Chronic otitis media is associated with calcification or ossification of suspensory
ligaments in MEC which leads to ossicular fixation. In few circumstances exact cause of
ossification of suspensory ligaments may not be known.
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Fig. 22: Ossification of the anterior malleal ligament (arrow). A few cob-web like
calcific foci (arrow head) are seen in attic, suggestive of tympanosclerosis.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
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Fig. 23: Calcification of the superior malleal ligament (arrow). Head of malleus is
eroded (arrow head). Background changes of chronic otitis media are seen.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
4. Congenital ossification of stapedius tendon (5*):
In normal circumstances the Stapedius tendon is not seen in entirety on CT and
considered abnormal whenever it is seen "too well". Congenital ossification of stapedial
tendon is a rare condition which causes CHL. It is indistinguishable from a congenital
bony bar in same region. Absence of background chronic otitis excluded the possibility
of tympanosclerosis.
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Fig. 24: Congenital ossification of the stapedius tendon (arrow). The stapes
superstructure (arrow head) and pyramidal eminence (star) are also seen.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
5. Bone forming tumor of MEC (6*):
Carcinoid tumor of MEC is a rare tumor and may show calcification within. It is otherwise
indistinguishable from other masses in MEC or that from chronic otitis media on the basis
of imaging alone. Clinically it presents as CHL.
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Fig. 25: Carcinoid tumor (black arrow head) with calcification (arrow) is seen in the
MEC. It is indistinguishable from chronic otitis media with tympanosclerosis on imaging.
Incus (white arrow head) is normal.
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
6. Large otosclerotic plaque projecting in the MEC:
Rarely exuberant new bone formation in an otosclerotic plaque at the margin of oval
window or on the footplate of stapes may appear heaped up and project in the MEC.
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Fig. 26: Thickened footplate of stapes (arrow head). A large plaque from the posterior
margin of oval window is projecting in obturator foramen of stapes (arrow).
References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/SG
Conclusion
Imaging with CT scan helps in finding cause of"too many" or "too few" osseous structures
in MEC which clinically may present as CHL or MHL.
References
1.
2.
CT of the Normal Suspensory Ligaments of the Ossicles in
the Middle Ear Marc M. Lemmerling,AJNR 18:471-477, Mar 1997
0195-6108/97/1803-0471).
Classification of congenital middle ear anomalies. Teunissen EB etal.
Ann Otol Rhinol Laryngol.1993 Aug;102(8 Pt 1):606-12 Teunissen EB etal.
Page 29 of 30
3.
4.
5.
6.
Postinflammatory ossicular fixation: CT analysis with surgical
correlation. Swartz JD, Wolfson RJ, Marlowe FI, et al. Radiology. 1985
Mar;154(3):697-700
Malleus Bar as a Rare Cause of Congenital Malleus Fixation: Yoshihisa
Kurosaki, et al AJNR Am J Neuroradiol 19:1229 -1230, August 1998.
Congenital ossification of the stapedius tendon: diagnosis with CT. Kurosaki
Y et al. Radiology. 1995 Jun;195(3):711-4.
Carcinoid tumor of the middle ear: clinical features, recurrences, and
metastases. Ramsey MJ et al. Laryngoscope 2005 Sep;115(9):1660.
Personal Information
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