Fracture Mimics on Temporal Bone CT: A Guide for the Radiologist

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1 Neuroradiology/Head and Neck Imaging Pictorial Essay Kwong et al. Temporal one Fracture Mimics on T Neuroradiology/Head and Neck Imaging Pictorial Essay Downloaded from by on 11/29/17 from IP address opyright RRS. For personal use only; all rights reserved Yune Kwong 1 David Yu Jagrit Shah Kwong Y, Yu D, Shah J Keywords: T, differential diagnosis, emergency radiology, skull fracture, temporal bone, trauma DOI: /JR Received September 30, 2011; accepted after revision November 16, ll authors: Department of Neuroradiology, Nottingham University Hospital, Derby Rd, Nottingham NG2 7UH, United Kingdom. ddress correspondence to Y. Kwong (dryune@hotmail.com). JR 2012; 199: X/12/ merican Roentgen Ray Society Fracture Mimics on Temporal one T: Guide for the Radiologist OJETIVE. The objective of this article is to discuss and illustrate commonly visualized fissures and sutures in the temporal bone. This topic is important because a thorough knowledge of normal anatomy is necessary to avoid misinterpretation as fractures. ONLUSION. Small normal anatomic fissures are now routinely visualized with the increasing use of MDT in trauma patients. n awareness of these structures is required by radiologists interpreting studies with fine temporal bone slices to prevent erroneous interpretation. T he use of MDT scanners for imaging trauma patients means that high-resolution images of the temporal bone are now routinely acquired and interpretation is no longer confined to specialist radiologists. The anatomy of the temporal bone is complex, and in particular, a number of normal fissures and channels are now routinely seen with thin-section T. In the context of trauma, these normal fissures and channels can lead to the pitfall of being interpreted as fractures, so a thorough knowledge of these pseudofractures is needed for correct interpretation [1, 2]. Temporal bone pseudofractures can be divided into three categories: intrinsic fissures, which are formed between the five parts of the temporal bone; extrinsic fissures, which are formed by the borders of the temporal bone with the rest of the cranial skeleton; and intrinsic channels, which are small connections that allow passage of various structures and are distinct from fissures. Intrinsic Fissures The temporal bone is composed of five distinct segments namely, the squamous, petrous, tympanic, mastoid, and styloid portions. Four intrinsic fissures around the bony part of the external auditory canal (E) can give the appearance of pseudofractures [3]. Tympanosquamous, Petrotympanic, Petrosquamous The tympanosquamous fissure is best seen anterior to the E (Fig. 1) and continues medially into the petrotympanic and petrosquamous fissures. The petrotympanic fissure (glaserian fissure) can be visualized on axial and sagittal images (Figs. 1 and 1). It provides an exit route for the chorda tympani from the middle ear to the infratemporal fossa and also allows passage of the anterior tympanic artery. The petrosquamous fissure is continuous with Koerner septum. On axial images, the petrosquamous fissure may be seen as a cleft oriented anteromedially from the glenoid fossa, but it is better seen on coronal images as a small defect in the tegmen tympani (Fig. 2). Tympanomastoid Suture Posterior to the E, the tympanomastoid fissure is an inconstant cleft that separates the E from the mastoid process (Fig. 3). The auricular branch of the vagus nerve, rnold nerve (which we describe later), emerges through the tympanomastoid suture. Extrinsic Fissures The temporal bone is separated from adjacent bones by a number of sutures. Frequently, a nonlinear course and sclerotic margins allow confident identification of these sutures. In other cases, knowledge of normal anatomy is required to prevent misinterpretation as fractures. Occipitomastoid Suture The occipitomastoid suture is consistently visualized posterior to the mastoid process (Fig. 4). It can have an asymmetric appearance or be bifid, causing difficulties in interpretation. 428 JR:199, ugust 2012

2 Temporal one Fracture Mimics on T Downloaded from by on 11/29/17 from IP address opyright RRS. For personal use only; all rights reserved On more cranial slices, its anterior continuation can appear to be a fractured fragment of temporal bone (Fig. 4); however, careful scrutiny will show this suture to be in continuity with the occipital bone. Petrooccipital Suture The petrooccipital suture starts at the petrous apex where it receives the inferior petrosal sinus. The suture extends caudad to the pars nervosa of the jugular foramen (Fig. 5), allowing the inferior petrosal sinus to join with the internal jugular vein. Sphenosquamosal Suture The sphenosquamosal suture is formed between the greater wing of the sphenoid bone and the squamous temporal bone. It is characteristically located lateral to the foramen spinosum (Fig. 6). Sphenopetrosal Suture The sphenopetrosal suture is situated between the posterior part of the greater wing of the sphenoid and the petrous apex (Fig. 7). It courses just posterior to the foramen ovale. The bony part of the eustachian tube is close and should not be confused with the sphenopetrosal suture. Intrinsic hannels The complex internal anatomy of the temporal bone means that several small channels can be mistaken for fractures by the uninitiated. In this section, the first five structures are presented from craniad to caudad. Petromastoid anal The petromastoid canal, also known as the subarcuate canaliculus, is recognized by its characteristic anteriorly convex course between the two limbs of the superior semicircular canal. Its caliber is usually equal to or less than the corresponding vestibular aqueduct [4] (Fig. 8). The petromastoid canal allows passage of the subarcuate artery, and dura also extends into the petromastoid canal. This canal can serve as a conduit for the intracranial spread of mastoid infection [5, 6]. Hiatus of the Facial anal The hiatus of the facial canal is on the anterior surface of the petrous pyramid and is continuous with the geniculate ganglion (Fig. 9). It allows exit of the greater superficial petrosal nerve to the middle cranial fossa. Singular anal The singular canal extends from the internal acoustic canal to the posterior semicircular canal (Fig. 10). The singular nerve (posterior ampullary nerve) passes through it, from the inferior vestibular nerve to the posterior semicircular canal. The singular canal is an important landmark during a retrosigmoid approach to vestibular schwannomas because its identification prevents accidental labyrinthine damage [7]. Vestibular queduct The vestibular aqueduct is a small canal extending from the vestibule to the posterior surface of the petrous bone (Fig. 11). It runs almost parallel to the petrous pyramid, and the full course is often best assessed on sagittal oblique images. The aqueduct contains the endolymphatic duct, which enlarges at its distal end to form the blind-ending endolymphatic sac. ochlear queduct The cochlear aqueduct extends from the subarachnoid space to the basal turn of the cochlea, close to the round window (Fig. 12). This relationship to the round window allows the cochlear aqueduct to be differentiated from the singular canal because both run in the same plane. The cochlear duct houses the perilymphatic duct, but there is controversy as to the patency of this duct in adults [8]. The medial aperture of the cochlear aqueduct is funnel-shaped (Fig. 12), and, caudad to that aperture, the glossopharyngeal sulcus opens into the jugular foramen (Fig. 12). Inferior Tympanic analiculus In the pars nervosa, the inferior tympanic branch (Jacobson nerve) arises from the glossopharyngeal nerve (Fig. 13) and ascends to the middle ear through the inferior tympanic canaliculus [9] (Fig. 14). The inferior tympanic artery also passes through; in an aberrant internal carotid artery (I) with absent petrous I, the inferior tympanic artery enlarges to form the proximal cranial I [10]. Mastoid analiculus The mastoid canaliculus transmits the auricular branch of the vagus nerve (rnold nerve) from the pars vascularis to the facial canal just above the stylomastoid foramen [11] (Figs. 13 and 15). The further course of the rnold nerve was described earlier in the Tympanomastoid Suture subsection and is shown in Figure 3. The courses of the Jacobson and rnold nerves are important to recognize not only because they can be confused with fractures, but also because paragangliomas have a predilection for occurring along their course [12]. onclusion This article reviews small sutures and channels that can cause confusion for the uninitiated, and knowledge of these sutures and channels will allow more confident interpretation of studies involving the temporal bone. References 1. Swartz JD. Temporal bone trauma. Semin Ultrasound T MR 2001; 22: onnor SE, Tan G, Fernando R, haudhary N. omputed tomography pseudofractures of the mid face and skull base. lin Radiol 2005; 60: Koesling S, Kunkel P, Schul T. Vascular anomalies, sutures and small canals of the temporal bone on axial T. Eur J Radiol 2005; 54: Krombach G, Schmitz-Rode T, Prescher, et al. The petromastoid canal on computed tomography. Eur Radiol 2002; 12: Tekdemir I, slan, Elhan. The subarcuate canaliculus and its artery: a radioanatomical study. nn nat 1999; 181: Migirov L, Kronenberg J. Petromastoid canal and cochlear aqueduct in cochlear implant candidates. Otolaryngol Head Neck Surg 2009; 140: girdir V, Sindel M, rslan G, et al. The canal of the posterior ampullar nerve: an important anatomic landmark in the posterior fossa transmeatal approach. Surg Radiol nat 2001; 23: Romo L, asselman J, Robson D. ongenital anomalies of the temporal bone. In: Som PM, utin HD, eds. Head and neck imaging. St. Louis, MO: Mosby, 2011: Tekdemir I, slan, Tüccar E, ubuk HE, Elhan H, Deda H. n anatomical study of the tympanic branch of the glossopharyngeal nerve (nerve of Jacobson). nn nat 1998; 180: Lo WW, Solti-ohman LG, McElveen JT Jr. berrant carotid artery: radiologic diagnosis with emphasis on high-resolution computed tomography. RadioGraphics 1985; 5: Tekdemir I, slan, Elhan. clinico-anatomic study of the auricular branch of the vagus nerve and rnold s ear-cough reflex. Surg Radiol nat 1998; 20: Weissman JL, Hirsch E. Imaging of tinnitus: a review. Radiology 2000; 216: JR:199, ugust

3 Kwong et al. Downloaded from by on 11/29/17 from IP address opyright RRS. For personal use only; all rights reserved Fig. 1 Tympanosquamous and petrotympanic sutures in 64-year-old man. and, T images show tympanosquamous suture (arrow, ) is anterior to bony external auditory canal (E) and continues medially as petrotympanic suture (arrows, ). ony portion of eustachian tube (arrowhead, ) is in proximity., Sagittal T reformation of petrotympanic fissure (arrow) shows that it connects middle ear with infratemporal fossa, thereby allowing passage of chorda tympani and anterior tympanic artery. Fig. 2 Petrosquamous fissure in 43-year-old man., T image shows petrosquamous fissure is continuation of Koerner septum (arrows). Petrosquamous fissure can be difficult to visualize on axial T., Petrosquamous fissure (arrow) is better seen on coronal reconstruction as small defect in tegmen tympani. Fig year-old girl. T image shows tympanomastoid fissure (arrows) is posterior to external auditory canal (E). uricular branch of vagus nerve (rnold nerve) passes through mastoid canaliculus (see Fig. 15) and emerges through this fissure to supply part of tympanic membrane and E. 430 JR:199, ugust 2012

4 Temporal one Fracture Mimics on T Downloaded from by on 11/29/17 from IP address opyright RRS. For personal use only; all rights reserved Fig. 5 Petrooccipital suture., T image of 23-year-old woman shows petrooccipital suture contains inferior petrosal sinus. Petrooccipital suture starts at petrous apex and extends caudad (arrowheads) into pars nervosa of jugular foramen., On T image of 46-year-old man with fracture of occipital bone (white arrows), petrooccipital suture (black arrows) can be differentiated from fracture line by its corticated margins, wavy outline, and opening into pars nervosa (p). Fig year-old woman. T image shows sphenopetrosal suture (white arrowheads) courses between greater wing of sphenoid bone and petrous apex. Sphenosquamosal suture is posterior to foramen ovale (asterisk). t same level, bony part of eustachian tube (black arrowhead) lies just posterior and lateral to sphenopetrosal suture. If it is not airfilled, bony part of eustachian tube may be confused with sphenopetrosal suture. Fig. 4 Occipitomastoid suture in 13-year-old girl., T image shows occipitomastoid suture (arrowheads); it is consistently seen posterior to mastoid process. symmetry of sutures is normal variant., From more cranial slice than, T image shows anterior part of suture (arrowhead). ppearance of suture can give impression of fractured fragment of temporal bone (asterisk), but scrolling back and forth will show that this fragment is in continuity with occipital bone. Fig year-old woman. T image shows sphenosquamosal suture (arrows) is between greater wing of sphenoid bone and squamous temporal bone. Sphenosquamosal suture is characteristically located lateral to foramen spinosum (arrowhead). JR:199, ugust

5 Kwong et al. Downloaded from by on 11/29/17 from IP address opyright RRS. For personal use only; all rights reserved Fig. 8 Petromastoid canal., T image of 61-year-old woman shows petromastoid canal (arrow) has characteristic anterior convex course from posterior fossa to mastoid antrum. It courses between two limbs of superior semicircular canal (arrowheads) and allows passage of subarcuate artery to otic capsule., T image from slice more caudal than shows vestibular aqueduct (arrowhead) of same patient. aliber of petromastoid canal is usually equal to or less than that of corresponding vestibular aqueduct., T image of 37-year-old man with longitudinal petrous fracture (white arrows) shows petromastoid canal (black arrow) as being separate because of its characteristic course. Fig. 9 Hiatus of facial canal., T image of 44-year-old woman. Hiatus of facial canal (arrow) is on anterior surface of petrous pyramid and is in continuity with geniculate ganglion (arrowhead). Greater superficial petrosal nerve exits through this hiatus., T image of 32-year-old man with transverse petrous fracture traversing internal auditory canal (I) (black arrows) shows hiatus of facial canal (white arrow) as being separate from fracture line by its continuity with geniculate ganglion and facial nerve canal posteriorly and I medially. Fig. 10 Singular canal in 13-year-old girl. and, Singular canal (arrow) can be visualized on both axial () and coronal () T images. It runs from posterior wall of internal auditory canal to junction of vestibule with posterior semicircular canal. Singular nerve (posterior ampullary nerve) runs through singular canal, from trunk of inferior vestibular nerve to posterior semicircular canal. 432 JR:199, ugust 2012

6 Temporal one Fracture Mimics on T Downloaded from by on 11/29/17 from IP address opyright RRS. For personal use only; all rights reserved Fig. 11 Vestibular aqueduct in 83-year-old man., xial T image shows vestibular aqueduct (arrow) borders posterior surface of petrous pyramid and runs almost parallel to it., Near its origin from vestibule, vestibular aqueduct (arrows) has reverse-j shape on T image., ecause of its obliquity, vestibular aqueduct (arrow) is often better seen on sagittal or sagittal oblique reconstruction. Sagittal plane is also best for assessing caliber of duct ( 1.5 mm). Fig. 12 ochlear aqueduct in 72-year-old man., T image shows cochlear aqueduct (arrow) arises from region of round window (arrowhead). This relationship to round window differentiates cochlear aqueduct from singular canal as both run along plane of internal acoustic canal., T image shows medial end of cochlear aqueduct (arrow) is wider and funnel-shaped., On slightly more caudal level than and, T image shows glossopharyngeal sulcus (arrow) conducts glossopharyngeal nerve to pars nervosa of jugular foramen. rrowhead indicates spine of jugular foramen. Fig. 13 T image illustrates courses of Jacobson nerve (J) and rnold nerve () in 72-year-old woman. These nerves are important because paragangliomas commonly occur along their courses. VII = mastoid segment of facial nerve, IX = glossopharyngeal nerve, X = vagus nerve, XI = accessory nerve, IPS = inferior petrosal sinus, JV = internal jugular vein. JR:199, ugust

7 Kwong et al. Fig. 14 Inferior tympanic canaliculus in 13-year-old girl., T image shows that Jacobson nerve arises from glossopharyngeal nerve in pars nervosa (asterisk) and runs in inferior tympanic canaliculus (arrows) between jugular foramen and carotid canal (cc)., On coronal T image, full course of Jacobson nerve (arrow) is seen as it ascends to hypotympanum to supply middle ear. Downloaded from by on 11/29/17 from IP address opyright RRS. For personal use only; all rights reserved Fig. 15 Mastoid canaliculus in 37-year-old man with sclerotic mastoid air cells., T image shows mastoid canaliculus (arrows), through which rnold nerve passes. It arises from pars vascularis and runs to facial nerve canal (arrowhead)., oronal T reconstruction shows mastoid canaliculus (arrow) opens into facial nerve canal a few millimeters above stylomastoid foramen (arrowhead). Further course of rnold nerve is described in Figure JR:199, ugust 2012