Download Fracture mimics on temporal bone CT - a guide for the

Fracture mimics on temporal bone CT - a guide for the
radiologist
Award:
Certificate of Merit
Poster No.:
C-0158
Congress:
ECR 2012
Type:
Educational Exhibit
Authors:
Y. Kwong, D. Yu, J. Shah; Nottingham/UK
Keywords:
CT, Trauma, Neuroradiology brain, Diagnostic procedure
DOI:
10.1594/ecr2012/C-0158
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Learning objectives
The objectives of this review are to illustrate small sutures and channels in the temporal
bone, which may be confused with fractures. The anatomical significance of these
'pseudo-fractures', in relation to the vessels and nerves, that pass through is discussed.
Background
Pseudo-fractures can be divided into three categories:
1) intrinsic fissures are the connections between the five parts of the temporal bone
2) extrinsic fissures are formed by the borders of the temporal bone with the rest of the
cranial skeleton
3) intrinsic channels are small connections that allow passage of various structures, and
are distinct from fissures.
Imaging findings OR Procedure details
Intrinsic Fissures
The temporal bone is composed of five distinct segments, namely the squamous, petrous,
tympanic, mastoid and styloid portions. Intrinsic fissures between these segments can
give the appearance of 'pseudofractures'. In particular, four intrinsic fissures can be seen
around the bony part of the external auditory canal (EAC).
Tympanosquamous, petrotympanic, petrosquamous
The tympanosquamous fissure is best seen anterior to the EAC (Figure 1), and continues
medially into the petrotympanic and petrosquamous fissures.
The petrotympanic (Glaserian) fissure can be visualized on axial and sagittal images
(Figure 2) and provides an exit route for the chorda tympani from the middle ear to the
infratemporal fossa. It also allows passage of the anterior tympanic artery from the first
part of the maxillary artery into the middle ear.
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The petrosquamous fissure is continuous with Koerner's septum, and on axial images,
may be seen as a cleft oriented anteromedially from the glenoid fossa, but is better
demonstrated on coronal images as a small defect in the tegmen tympani (Figure 3).
Tympanomastoid suture
Posteriorly, the tympanomastoid fissure is an inconstant cleft that separates the bony
EAC from the mastoid process (Figure 4). The auricular branch of the vagus nerve
(Arnold's nerve) passes through the mastoid canaliculus and emerges through the
tympanomastoid suture to supply sensation to a small part of the tympanic membrane
and external auditory meatus.
Extrinsic fissures
Occipitomastoid suture
The occipitomastoid suture is consistently visualised posterior to the mastoid process
(Figure 5). It can have an asymmetrical appearance and be bifid causing difficulties in
interpretation. On more cranial slices, its anterior continuation can give the appearance
of a fractured piece of temporal bone, but careful scrutiny will show this to be in continuity
with the main occipital bone.
Petro-occipital suture
The petro-occipital suture starts at the petrous apex, where it receives the inferior petrosal
sinus from the cavernous sinus. The suture extends caudally, where it can be followed
to the pars nervosa of the jugular foramen (Figure 6), allowing the inferior petrosal sinus
to join with the internal jugular vein.
Sphenosquamosal suture
This is the suture between the greater wing of the sphenoid and the squamous temporal
bone. It is characteristically located lateral to the foramen spinosum (Figure 7)
Sphenopetrosal suture
The sphenopetrosal suture is situated between the posterior part of the greater wing of
the sphenoid and the petrous apex (Figure 8). It courses just posterior to the foramen
ovale.
Intrinsic Channels
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Petromastoid canal
The petromastoid canal (also known as the subarcuate canaliculus) is recognised by its
characteristic anteriorly convex course between the two limbs of the superior semicircular
canal (Fig. 9). The petromastoid canal allows passage of the subarcuate artery to the otic
capsule, and dura also extends into the petromastoid canal. This can serve as a conduit
for the intracranial spread of mastoid infection.
Hiatus of the facial canal
This hiatus is on the anterior surface of the petrous pyramid, and is continuous with the
geniculate ganglion (Fig. 10). It allows exit of the greater superficial petrosal nerve to the
middle cranial fossa.
Singular canal
The singular canal extends from the internal acoustic canal to the posterior semicircular
canal (Fig. 11). The singular nerve (posterior ampullary nerve) passes through, from the
inferior vestibular nerve to the posterior semicircular canal. It is an important landmark
during retrosigmoid approach to vestibular schwannomas, as its identification prevents
accidental labyrinthine damage.
Vestibular aqueduct
The vestibular aqueduct is a small canal extending from the vestibule to the posterior
surface of the petrous bone (Fig. 12), and runs almost parallel to the petrous pyramid.
The aqueduct contains the endolymphatic duct, which enlarges at its distal end to form
the blind-ending endolymphatic sac.
Cochlear aqueduct
The cochlear aqueduct extends from the subarachnoid space to the basal turn of the
cochlea, close to the round window (Fig. 13). This relationship to the round window allows
the cochlear aqueduct to be differentiated from the singular canal, as both run in the same
plane. The medial aperture of the cochlear aqueduct is funnel-shaped. The cochlear duct
houses the perilymphatic duct, but there is controversy as to the patency of this duct in
adults.
Inferior tympanic canaliculus
In the pars nervosa, the inferior tympanic branch (Jacobson's Nerve) arises from the
glossopharyngeal nerve, and ascends to the middle ear through the inferior tympanic
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canaliculus. This is demonstrated on axial and coronal images (Fig. 14). The inferior
tympanic artery also passes through, and in an aberrant ICA with absent petrous ICA,
the inferior tympanic artery enlarges to form the proximal cranial ICA.
Mastoid canaliculus
The mastoid canaliculus transmits the auricular branch of the vagus nerve (Arnold's
nerve) from the pars vascularis to the facial canal just above the stylomastoid foramen
(Figs 15). The course of Jacobson's and Arnold's nerves are important to recognize
not only to avoid confusion with fractures, but also because paragangliomas have a
predilection for occurring along their course.
Images for this section:
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Fig. 1: Tympanosquamous suture is seen anterior to the bony external auditory meatus.
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Fig. 2: Petrotympanic suture (black arrows), with the Eustachian tube (white arrowhead)
closely related. Sagittal reformats (white arrow) of the petrotympanic fissure show that it
is a connection between the middle ear and infratemporal fossa.
Fig. 3: The petrosquamous fissure is the continuation of Koerner's septum (arrows), and
is better seen on coronal reconstructions (arrow).
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Fig. 4: The tympanomastoid fissure (arrows)
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Fig. 5: Occipitomastoid suture (black arrowheads). The anterior part of the suture (white
arrowhead) can simulate a fractured piece of temporal bone (asterisk).
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Fig. 6: The petro-occipital suture
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Fig. 7: Sphenosquamosal suture (arrows) is lateral to the foramen spinosum (arrowhead)
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Fig. 8: The sphenopetrosal suture (white arrowheads) is medial to the foramen ovale
(asterisk). Note the proximity of the Eustachian tube (black arrowhead)
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Fig. 9: The petromastoid or arcuate canal (arrow) courses between the limbs of the
superior semicircular canal (arrowhead)
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Fig. 10: The hiatus of the facial canal (white arrow) is in continuity with the geniculate
ganglion (black arrowhead).
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Fig. 11: The singular canal
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Fig. 12: The vestibular aqueduct (arrow). Near its origin from the vestibule, the vestibular
aqueduct has a reverse-J shape.
Fig. 13: The cochlear aqueduct
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Fig. 14: Jacobson's nerve arises from the glossopharyngeal nerve in the pars nervosa
(asterisk), and runs in the inferior tympanic canaliculus (arrows), between the jugular
foramen and the carotid canal (cc). On the coronal plane, the full course of Jacobson's
nerve (arrow) is seen, as it ascends to the hypotympanum to supply the middle ear.
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Fig. 15: The mastoid canaliculus (arrows) runs to the facial nerve canal (arrowhead)
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Conclusion
The anatomy of the temporal bone is complex, and correct identification of normal
structures is necessary to prevent misinterpretation as fractures. This article reviews
small sutures and channels that can cause confusion for the uninitiated, and this will allow
more confident interpretation of studies involving the temporal bone.
Personal Information
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