Fracture mimics on temporal bone CT - a guide for the ... · nerve) from the pars vascularis to the...

of 20

Fracture mimics on temporal bone CT - a guide for theradiologist

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

Any information contained in this pdf file is automatically generated from digital materialsubmitted to EPOS by third parties in the form of scientific presentations. Referencesto any names, marks, products, or services of third parties or hypertext links to third-party sites or information are provided solely as a convenience to you and do not inany way constitute or imply ECR's endorsement, sponsorship or recommendation of thethird party, information, product or service. ECR is not responsible for the content ofthese pages and does not make any representations regarding the content or accuracyof material in this file.As per copyright regulations, any unauthorised use of the material or parts thereof aswell as commercial reproduction or multiple distribution by any traditional or electronicallybased reproduction/publication method ist strictly prohibited.You agree to defend, indemnify, and hold ECR harmless from and against any and allclaims, damages, costs, and expenses, including attorneys' fees, arising from or relatedto your use of these pages.Please note: Links to movies, ppt slideshows and any other multimedia files are notavailable in the pdf version of presentations.www.myESR.org

of 20

Learning objectives

The objectives of this review are to illustrate small sutures and channels in the temporalbone, 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 thecranial skeleton

3) intrinsic channels are small connections that allow passage of various structures, andare 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 cangive the appearance of 'pseudofractures'. In particular, four intrinsic fissures can be seenaround 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 continuesmedially 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 theinfratemporal fossa. It also allows passage of the anterior tympanic artery from the firstpart of the maxillary artery into the middle ear.

of 20

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 betterdemonstrated 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 bonyEAC from the mastoid process (Figure 4). The auricular branch of the vagus nerve(Arnold's nerve) passes through the mastoid canaliculus and emerges through thetympanomastoid suture to supply sensation to a small part of the tympanic membraneand 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 ininterpretation. On more cranial slices, its anterior continuation can give the appearanceof a fractured piece of temporal bone, but careful scrutiny will show this to be in continuitywith the main occipital bone.

Petro-occipital suture

The petro-occipital suture starts at the petrous apex, where it receives the inferior petrosalsinus from the cavernous sinus. The suture extends caudally, where it can be followedto the pars nervosa of the jugular foramen (Figure 6), allowing the inferior petrosal sinusto join with the internal jugular vein.

Sphenosquamosal suture

This is the suture between the greater wing of the sphenoid and the squamous temporalbone. 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 ofthe sphenoid and the petrous apex (Figure 8). It courses just posterior to the foramenovale.

Intrinsic Channels

of 20

Petromastoid canal

The petromastoid canal (also known as the subarcuate canaliculus) is recognised by itscharacteristic anteriorly convex course between the two limbs of the superior semicircularcanal (Fig. 9). The petromastoid canal allows passage of the subarcuate artery to the oticcapsule, and dura also extends into the petromastoid canal. This can serve as a conduitfor 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 thegeniculate ganglion (Fig. 10). It allows exit of the greater superficial petrosal nerve to themiddle cranial fossa.

Singular canal

The singular canal extends from the internal acoustic canal to the posterior semicircularcanal (Fig. 11). The singular nerve (posterior ampullary nerve) passes through, from theinferior vestibular nerve to the posterior semicircular canal. It is an important landmarkduring retrosigmoid approach to vestibular schwannomas, as its identification preventsaccidental labyrinthine damage.

Vestibular aqueduct

The vestibular aqueduct is a small canal extending from the vestibule to the posteriorsurface 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 formthe blind-ending endolymphatic sac.

Cochlear aqueduct

The cochlear aqueduct extends from the subarachnoid space to the basal turn of thecochlea, close to the round window (Fig. 13). This relationship to the round window allowsthe cochlear aqueduct to be differentiated from the singular canal, as both run in the sameplane. The medial aperture of the cochlear aqueduct is funnel-shaped. The cochlear ducthouses the perilymphatic duct, but there is controversy as to the patency of this duct inadults.

Inferior tympanic canaliculus

In the pars nervosa, the inferior tympanic branch (Jacobson's Nerve) arises from theglossopharyngeal nerve, and ascends to the middle ear through the inferior tympanic

of 20

canaliculus. This is demonstrated on axial and coronal images (Fig. 14). The inferiortympanic 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'snerve) 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 recognizenot only to avoid confusion with fractures, but also because paragangliomas have apredilection for occurring along their course.

Images for this section:

of 20

Fig. 1: Tympanosquamous suture is seen anterior to the bony external auditory meatus.

of 20

Fig. 2: Petrotympanic suture (black arrows), with the Eustachian tube (white arrowhead)closely related. Sagittal reformats (white arrow) of the petrotympanic fissure show that itis a connection between the middle ear and infratemporal fossa.

Fig. 3: The petrosquamous fissure is the continuation of Koerner's septum (arrows), andis better seen on coronal reconstructions (arrow).

of 20

Fig. 4: The tympanomastoid fissure (arrows)

of 20

Fig. 5: Occipitomastoid suture (black arrowheads). The anterior part of the suture (whitearrowhead) can simulate a fractured piece of temporal bone (asterisk).

of 20

Fig. 6: The petro-occipital suture

of 20

Fig. 7: Sphenosquamosal suture (arrows) is lateral to the foramen spinosum (arrowhead)

of 20

Fig. 8: The sphenopetrosal suture (white arrowheads) is medial to the foramen ovale(asterisk). Note the proximity of the Eustachian tube (black arrowhead)

of 20

Fig. 9: The petromastoid or arcuate canal (arrow) courses between the limbs of thesuperior semicircular canal (arrowhead)

of 20

Fig. 10: The hiatus of the facial canal (white arrow) is in continuity with the geniculateganglion (black arrowhead).

of 20

Fig. 11: The singular canal

of 20

Fig. 12: The vestibular aqueduct (arrow). Near its origin from the vestibule, the vestibularaqueduct has a reverse-J shape.

Fig. 13: The cochlear aqueduct

of 20

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 jugularforamen and the carotid canal (cc). On the coronal plane, the full course of Jacobson'snerve (arrow) is seen, as it ascends to the hypotympanum to supply the middle ear.

of 20

Fig. 15: The mastoid canaliculus (arrows) runs to the facial nerve canal (arrowhead)

of 20

Conclusion

The anatomy of the temporal bone is complex, and correct identification of normalstructures is necessary to prevent misinterpretation as fractures. This article reviewssmall sutures and channels that can cause confusion for the uninitiated, and this will allowmore confident interpretation of studies involving the temporal bone.

Personal Information

References

1. Swartz JD. Temporal bone trauma. Semin. Ultrasound CT MR 2001; 22(3):219-228

2. Connor SEJ, Tan G, Fernando R, et al. Computed tomography pseudofractures of themid face and skull base. Clin Radiol 2005; 60(12):1268-1279

3. Koesling S, Kunkel P, Schul T. Vascular anomalies, sutures and small canals of thetemporal bone on axial CT. Eur J Radiol 2005; 54(3):335-343

4. Krombach GA, Schmitz-Rode T, Prescher A, et al. The petromastoid canal oncomputed tomography. Eur Radiol 2002; 12(11):2770-2775

5. Tekdemir I, Aslan A, Elhan A. The subarcuate canaliculus and its artery - aradioanatomical study. Ann. Anat. 1999; 181(2):207-211

6. Migirov L, Kronenberg J. Petromastoid canal and cochlear aqueduct in cochlearimplant candidates. Otolaryngol Head Neck Surg 2009; 140(3):419-422

7. Agirdir BV, Sindel M, Arslan G, et al. The canal of the posterior ampullar nerve: animportant anatomic landmark in the posterior fossa transmeatal approach. Surg RadiolAnat 2001; 23(5):331-334

8. Romo L, Casselman J, Robson, CD. Congenital anomalies of the temporal bone.In: Som PM, Cutin HD, ed. Head and Neck Imaging. St Louis, Missouri: Mosby,2011:1097-1165

9. Tekdemir I, Aslan A, Tüccar E, et al. An anatomical study of the tympanic branch ofthe glossopharyngeal nerve (nerve of Jacobson). Ann. Anat. 1998; 180(4):349-352

of 20

10. Lo WW, Solti-Bohman LG, McElveen JT Jr. Aberrant carotid artery: radiologicdiagnosis with emphasis on high-resolution computed tomography. Radiographics 1985;5(6):985-993

11. Tekdemir I, Aslan A, Elhan A. A clinico-anatomic study of the auricular branch of thevagus nerve and Arnold's ear-cough reflex. Surg Radiol Anat 1998; 20(4):253-257

12.Weissman JL, Hirsch BE. Imaging of tinnitus: a review. Radiology 2000;216(2):342-349

Fracture mimics on temporal bone CT - a guide for the ... · nerve) from the pars vascularis to the...

Documents

Transcript of Fracture mimics on temporal bone CT - a guide for the ... · nerve) from the pars vascularis to the...