Download Imaging of anatomical variations of the temporal bone to specify to

Imaging of anatomical variations of the temporal bone to
specify to the surgeon before middle ear surgery
Poster No.:
C-2514
Congress:
ECR 2013
Type:
Educational Exhibit
Authors:
H. Zaghouani , N. Benzina , C. H. ZARRAD , W. Kermani , M.
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Limeme , S. MAJDOUB , H. Amara , D. Bakir , C. Kraeim ;
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Sousse, DEPARTMENT OF RADIOLOGY, FARHAT HACHED
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HOSPITAL, SOUSSE/TN, Sousse, DEPARTMENT OF
RADIOLOGY, FARHAT HACHED HOSPITAL, SOUSSE/TN,
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Sousse, Department of Ear, Nose, and Throat, Farhat Hached
University Hospital, Sousse, Tunisia/TN
Keywords:
Ear / Nose / Throat, Head and neck, Bones, CT, Structured
reporting, Surgery, Congenital
DOI:
10.1594/ecr2013/C-2514
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Learning objectives
Illustrate the anatomical variations of the temporal bone that the radiologist must know.
Emphasize the importance of signaling them to the surgeon before middle ear surgery.
Background
The anatomical variations of the temporal bone can be a hindrance to the surgical incision
or predispose to intraoperative incidents or failure of the surgical procedure. Signaling
these variations to the surgeon preoperatively is important to guide and adjust the surgical
intervention.
Imaging findings OR Procedure details
Important Anatomical Variations Of The Temporal Bone
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Facial Nerve Dehiscence And Procidence
The frequency of FND varies from 0.5% to 74%.
Mostly occurs in the tympanic segment near the oval window.
Severe anomalies of the course of the facial nerve occur in the tympanic and vertical
portions.
The horizontal segment at times is displaced inferiorly to cover the oval window or lies
exposed over the promontory. The facial canal is usually rotated laterally. The rotation
varies a minor obliquity to a true horizontal course.
•
Dural Exposure
The tegmen of the mastoid and attic passes usually in a horizontal plane slightly lower
than the arcuate eminence produced by the top of the superior semicircular canal.
A depression of the tegmental plate is not unusual; the floor of the middle cranial fossa
deepens to form a groove lateral to the attic and to the labyrinth. The low hanging dura
may cover the roof of the external auditory canal.
Operative risk: risk of penetration of the cranial cavity during surgery .
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•
Variations Of Jugular Bulb (High , Asymetric, Procident Jugular Bulb)
A variable anatomy of the jugular bulb is not rare and usually it manifests as a high jugular.
A High Positioned Jugular Bulb with or without Bony Covering
The upper portion of the jugular bulb normally lies below the floor of the hypotympanium
of the middle ear space.
Clinically, this variant without bony covering seems to be much more important than that
with bony covering, because it can be otologically misdiagnosed as a glomus tumour.
On the CT, however, the glomus tumour can be effectively excluded by its pattern.
Operative risk: extensive haemorrhage at myringotomy or exploratory tympanotomy .
Dehiscence of jugular bulb : an incomplete bony covering of jugular bulb.
A Dehiscent jugular bulb protrudes into the middle ear it can be confused with a glomus
tumor by otoscopy.
Operative risk: Bleeding complications during middle ear procedures.
Diverticulum of jugular bulb: a rare entity; is the superior and medial extension of the
jugular bulb into the bone of the posterior wall of the internal auditory canal. A high jugular
bulb with or without a diverticulum has influence on the approach in acoustic neurinoma
surgery.
Severe Asymmetry of the Jugular Foramen
The difference can be up to 18 mm, when it is greater than or equal to 2 cm, it must be
considered pathological.
The search for this asymmetry serves only to distinguish from the pathology as it is quite
common and quite normal and asymptomatic.
Enlargement of the jugular foramen also occurs in tumours of the glomus jugulare, and
neuromas of cranial nerves IX, X and XI. An irregular erosion of its margin and an erosion
of the jugular spine are frequently seen in pathological conditions. This is an important
differentiation between the normal and abnormal jugular foramen.
•
Position Of Sigmoid Sinus : An Anteriorly Located Sigmoid Sinus
The sigmoid sinus forms a shallow indentation on the posterior aspect of the mastoid.
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Occasionally the sinus courses more anteriorly and produces a deep groove in the
mastoid, best seen in the axial sections. In some cases only a thin bony plate separates
the sinus from the external auditory canal.
The distance of the anterior wall of the sigrnoid sinus to the posterior wall of the external
auditory canal determines the amount of space for the postauricular approach to the
mastoid antrum.
Operative implication: If the anterior wall of the sigmoid sinus is anteriorly located, the
postauricular approach may be impossible. This distance should be evaluated on the CJ
before surgery of the mastoid antrum.
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Körner's Septum
Körner's septum (KS) refers to a dense, bony plate found in the mastoid process which
represents the persistence of the petrosquamous suture line. This septum, when present,
divides the mastoid process into a superficial squamous portion and a deep petrous
portion.
KS is an anatomical structure that may create problems or complications during
mastoidectomy . In case of antral cholesteatoma and in the absence of signaling the
presence of a thick septum Korner to the surgeon, there is a risk of incomplete emptying
of the antrum.
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Aberrant Internal Carotid Artery
An aberrant internal carotid artery (AICA) is a rare vascular anomaly taking an aberrant
lateral course in the temporal bone and passes through the middle ear cavity.
Operative risk: extensive hemorrhage
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Mastoid Aeration
There are different types of pneumatization
The temporal bone is:
* Pneumatic when pneumatization is complete
* Diploïc when it is partial
* Sclerotic or compact when it is absent
The absence of tegmental air cells causes a risk of harm of cranial fossa surgery of
chronic otitis media cholesteatoma or not or its aftermath)
•
Deep Sinus Tympani
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The sinus tympani is the bony recess which lies medial to the pyramidal eminence,
stapedial muscle and facial canal.
Frequently, involved by chronic infection and secondary cholesteatomas.
For the otologic surgeon, demonstration of precise anatomy of the sinus tympani is
necessary before surgery.
Their measurement of the depth of the sinus tympani on axial section ranged from 0.61
to 5.87mm (average 2.93mm).
Evaluation of the sinus tympani is important as it will determine the surgical approach,
and as it is a blind zone for the ENT surgeon, source of recurrence of cholesteaatoma.
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Anterior Epitympanic Recess
It is a pneumatic cell of variable size sitting antero-medially to the mallear head.
The proximal segment of the facial nerve tympanic seats immediately inward of the recess
At this level, the cholesteatoma has a direct access to the facial nerve.
The bone spur, laterally bounding this space corresponds to the proximal extremity of
the petro-squamous suture
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Hypoplasia Of The Middle Ear
The width of the tympanic cavity is measured from the promontory to the sidewall
This measurement must be performed in a coronal plane.
Width lower than 3 mm makes surgery of the middle ear inadequate.
Insufficient development of the tympanic cavity and mastoid antrum may pose difficulties
to the surgeon by limiting the space of the operative field.
This anomaly is often associated with abnormalities of the ossicular chain.
Images for this section:
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Fig. 1: coronal view dehisence of the bony canal of the facial nerve
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Fig. 2: coronal view. procidence and dehiscence of the bony canal of the facial nerve
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Fig. 3: axial view asymetric jugular bulb
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Fig. 4: axial view An Anteriorly Located Sigmoid Sinus High Positioned Jugular Bulb
without Bony Covering
Fig. 5: axial view. An Anteriorly Located Sigmoid Sinus. High Positioned Jugular Bulb
without Bony Covering.
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Fig. 9: axial view. mastoid hyperpneumatisation
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Fig. 8: axial view mastoid hypopneumatisation
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Fig. 7: axial view. thick Korner's septum
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Fig. 6: axial view. An Anteriorly Located Sigmoid Sinus
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Fig. 10: axial view. Deep Sinus Tympani
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Conclusion
Recognition of aberrant internal carotid artery, facial nerve dehiscence, low hanging dura,
high jugular bulb, anterior placed sigmoid sinus radiologically prior to mastoid surgery
is imperative. Preoperative CT scan is mandatory in the evaluation of detailed anatomy
of the temporal bone and decreases the possibility of surgical complications as well as
surgical revision for insufficient treatment.
References
Analysis of Anatomic Variations in Temporal Bone by Radiology
Cigdem Tepe Karaca, Sema Zer Toros, Hulya Kahve Noseri, The Journal of International
Advanced Otology
Personal Information
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