Imaging of Temporal Bone Trauma

Pratik Mukherjee

Contents 1 Pseudo-fractures 127 2 Imaging Approach 129 3 Temporal Bone Fractures 129 4 Complications 131 5 What the Surgeon Wants to Know (Table 5) 133 Suggested Reading 133

Abstract of temporal bone fractures and complica- tions. Quick reference checklists for potential Temporal bone trauma is a frequently encoun- complications, ossicular chain disruptions tered clinical issue that requires careful eval- and important surgical descriptors are pro- uation and precise description in order to vided as well. exclude serious complications and guide sur- gical interventions when necessary. This chapter discusses the appropriate trauma imaging strategy based on various clinical 1 Pseudo-fractures settings, reviews the normal anatomy that could potentially mimic fractures, i.e. pseudo- The temporal bones are complex paired bony fractures and elaborates on the different types structures that have a myriad of fssures or sutures and are traversed by numerous channels, all of which can potentially be mistaken for fractures. P. Mukherjee (*) Fissures that form between the fve native Department of Diagnostic Radiology, Woodlands parts of the temporal bone are called “intrinsic” Health Campus, Singapore, Singapore and are located around the external ear canal e-mail: [email protected]

© Springer Nature Switzerland AG 2021 127 G. G. Pulickal et al. (eds.), Temporal Bone Imaging Made Easy, Medical Radiology Diagnostic Imaging, https://doi.org/10.1007/978-3-030-70635-7_18 128 P. Mukherjee

(EAC). Those fssures that form between the tem- poral bone and the rest of the skull bones are termed “extrinsic fssures” (Figs. 1 and 2) (Table 1).

Fig. 3 Axial CT image shows the faint petromastoid Fig. 1 Axial CT image shows the following extrinsic fs- canal (arrow) traversing between the anterior and posterior sures, i.e. the petro-occipital (black arrow), sphenopetro- limbs of the superior semi-circular canals, it should always sal (black dashed arrow), sphenosquamosal (white arrow) be equal or smaller in calibre than the semi-circular­ canals and the occipitomastoid (white dashed) fssures as well as the intrinsic tympanosquamous fssure (thick white arrow)

Fig. 4 Axial CT image shows an opening along the ante- Fig. 2 Sagittal CT shows the petrotympanic fssure rior surface of the petrous apex that is in continuation with (arrow) containing the chorda tympani nerve, extending the geniculate ganglion termed the hiatus of the facial nerve, from the middle ear to the temporomandibular joint through which the greater superfcial petrosal nerve exists

Table 1 Normal fssures and intrinsic channels Extrinsic fssures Intrinsic fssures Intrinsic channels Sphenosquamosal Tympanosquamous Cochlear and vestibular aqueducts (refer Sect. 1 in chapter “Basic Temporal Bone Imaging Anatomy: External, Middle and Inner Ear”) Sphenopetrosal Petrotympanic Mastoid and inferior tympanic canaliculi (refer Sect. 5 in chapter “Imaging of the Petrous Apex, Cerebellopontine Angles and Jugular Foramen”) Occipitomastoid Petrosquamous Petromastoid (subarcuate) canal (Fig. 3) Petrooccipital Tympanomastoid Hiatus of the facial canal (Fig. 4) Singular nerve canal (Fig. 5) Imaging of Temporal Bone Trauma 129

Fig. 6 Oblique CT reconstruction of the malleoincudal Fig. 5 Axial CT image shows the singular canal (arrow) joint shows the anteriorly located malleus head (arrow) transmitting the singular nerve from the IAC to the poste- articulating with the facet of the incus rior semi-circular canal. Note the post-traumatic changes in the temporal bone with patchy opacifcations of the mastoid air cells and EAC within vestibular nucleus or nerve root entry zone. 2 Imaging Approach • In established CSF otorrhea, high-­ resolution T2w sequences can detect High-resolution CT scan with axial fne cuts encephaloceles and pinpoint the exact (preferably sub-1 mm thickness and small feld site of CSF leak. Contrast is useful in of view i.e. <10 cm) and multiplanar reconstruc- such cases to look for dural enhance- tions is the imaging of choice. Conventional axial ment which is a secondary sign of and coronal views may not always display the dural tear, CSF leak and possible integrity of the ossicular chain adequately; hence, meningitis. multiplanar reformations (MPR) should be used • In post-traumatic facial palsy without to overcome this limitation. The idea is to refor- any obvious temporal bone fracture, mat oblique planes in line with the long axis of MRI can demonstrate abnormal nerve each individual bone or joint to obtain a holistic and dural enhancement along the tem- view (refer Sect. 1 in chapter “Temporal Bone poral bone, probably due to tears from Imaging Techniques: Computer Tomography, micro (occult) fractures Cone Beam CT and Magnetic Resonance Imaging”) (Fig. 6).

3 Temporal Bone Fractures

MRI in Temporal Bone Trauma Patients with head injury undergo a preliminary • MRI has only limited role and should CT head in the emergency department, and gross only be used as a problem-solving tool. temporal bone fractures are usually readily iden- • In persistent post-traumatic vertigo tifable. Subtle fractures can be more challeng- where initial CT evaluation did not show ing, and clinicians and radiologists should be any abnormality, gradient echo aware of some clinical and imaging fndings that sequences can detect haemorrhage are suggestive of temporal bone fractures (Table 2). 130 P. Mukherjee

Table 2 Clinical signs and imaging fndings on computed tomography of head which are highly suggestive of temporal bone involvement Clinical fndings suspicious for temporal bone fracture Indirect imaging signs of temporal bone fracture Blunt head injury and Racoon eyes (periorbital Pneumocephalus adjacent to the temporal bone ecchymosis) Epidural haematoma (middle meningeal artery injury) Blood in external auditory canal Air in the temporomandibular joint (Fig. 7) Blood in the external ear Mastoid and/or middle ear opacifcation (Fig. 7) Hearing loss, vertigo, imbalance or facial paralysis Pneumolabyrinth (Fig. 8)

Fig. 8 Axial CT image shows a mixed temporal bone fracture with longitudinal (white arrow) and transverse (dashed arrow) components violating the otic capsule. A focus of pneumolabyrith is seen within the vestibule

as it helps in communicating the fndings to the Fig. 7 Axial CT image does not show any obvious tem- referrer. poral bone fracture but air in the temporomandibular joint Alternatively, more clinical classifcation sys- (dashed arrow) and patchy opacifcation of the mastoid air tems were developed, e.g. broadly classifying cells (arrow) are highly suggestive of a traumatic temporal them into petrous and non-petrous or otic-sparing bone injury and otic-violating fractures. The otic-violating fractures involve the labyrinth (cochlea, vestibule Temporal bone fractures are classically and semi-circular canals) and are commonly divided into longitudinal, transverse and mixed associated with SNHL, CSF fstula and facial fractures (Table 3) based on the orientation of the nerve injury (Fig. 8). The most popular way is a fracture to the petrous segment of the temporal combined approach, describing the direction of bone. Unfortunately, this classifcation does not fracture (traditional), location along the temporal predict potential complications; hence it is of bone and involvement of the bony labyrinth/otic limited clinical use. Nevertheless, it is still in use capsule (clinical). Imaging of Temporal Bone Trauma 131

Table 3 Review of different types of fractures of temporal bone Type of fracture Incidence Mechanism Imaging fndings Longitudinal 70–90% • Temporo-parietal • Fracture parallel to long axis of petrous segment (Fig. 9) cases impact on the head • Fracture can involve EAC, tympanic cavity and squamous • The force being segment of temporal bone directed laterally • Usually spares the inner ear to medial along • Ossicular chain disruptions are more common the long axis of • Subtypes the temporal bone – Anterior; fracture plane extends anteriorly towards the Eustachian tube and middle cranial fossa (more common) – Posterior; fracture extends behind the bony labyrinth to involve jugular foramen and posterior fossa (rarer) Transverse 10–20% • Blow to the back • Fracture perpendicular to long axis of petrous segment cases or front of the • Subtypes (depending on position of the fracture line head relative to arcuate eminence) • Force direction is – Medial; transgresses at or medial to lateral most along antero- aspect of internal auditory canal posterior axis – Lateral; transgresses bony labyrinth Mixed (Fig. 8) • Combination of both longitudinal and transverse fractures

Table 4 Complications of temporal bone trauma based on location and symptoms Symptoms Imaging fndings CHL • Blood in the EAC and Haemotympanum (transient) • TM perforation • Ossicular chain disruption (Figs. 9, 10, 11 and 12) SNHL • Otic capsule violation and • IAC injury vertigo • Pneumo or haemolabyrinth (MRI for Fig. 9 Axial CT images showing a characteristic otic the latter) → Labyrinthitis ossifcans sparing longitudinal fracture that extends into the middle • Nerve root entry zone injury or ear cavity (black arrow) and causes widening/subluxation transection (MRI better) of the incudomalleolar joint (white arrow) CSF • Tegmen fracture (Fig. 13) otorrhea • Stapes footplate-oval window injury • Round window involvement 4 Complications Facial • Up to 50% in transverse fractures nerve • Fracture line through the facial nerve Temporal bone injuries can give rise to numerous palsy canal, usually in the tympanic part. complications; while some like CHL, SNHL and Usually with a bony fragment impinging on the canal (acute) vertigo are rather common, others like otorrhea • Post-traumatic oedema or and facial paralysis are less common. Use the haemorrhage involving facial nerve table below as quick reference for the potential canal; fracture may be absent (delayed causes behind these symptoms (Table 4). presentation) Adapted from Kennedy et al. (2014)

Tip SNHL, vertigo etc. The site of communica- • Perilymphatic fstula is a rare complication tion can be the oval or round windows or that results due to an abnormal connection the otic capsule. between the aerated middle ear and the • Presence of a middle ear effusion with fuid-flled inner ear. opacifcation of the windows or presence of • Patients can present with a variety of symp- a pneumolabyrinth should raise suspicion toms including ear fullness, tinnitus, of a fstula. 132 P. Mukherjee

Post-traumatic Ossicular Chain Disruption • Incudostapedial injury (subluxation or dislocation) is the most common trauma-related injury of the ossicles (Fig. 10), but often diffcult to diagnose in the acute setting with haemotympa- num often obscuring the joint. • Incudostapedial joint is best seen on oblique reformations perpendicular to the oval window (refer Sect. 1 in chapter “Temporal Bone Imaging Techniques: Computer Tomography, Cone Beam CT Fig. 11 Coronal CT in a post-traumatic patient (note the and Magnetic Resonance Imaging”). haemotympanum and blood in the EAC) shows widening • Malleoincudal subluxations may not be of malleoincudal joint (“broken heart sign”) readily apparent on axial planes and hence needs to be evaluated on coronal planes as well (Fig. 11). • The intact malleoincudal complex can be displaced en bloc, usually into the meso-tympanum (Fig. 12). • If the incudostapedial and the malleoin- cudal joints are disrupted; then, the incus is said to be totally dislocated. Fig. 12 Coronal CT image showing the malleoincudal • Stapediovestibular dislocations and complex being displaced inferiorly (arrow) from the epi- ossicular fractures are very rare. tympanum into the mesotympanum. Note the normal con- tralateral side for comparison

Fig. 10 Coronal CT image of a patient presenting with post-traumatic (note the deformity of the EAC) conduc- tive hearing loss. There is complete dislocation of the Fig. 13 Coronal CT image of a patient with post-­ incudostapedial joint with lentiform process of the incus traumatic otorrhea shows a tegmen fracture (black arrow) (arrow) failing to articulate with the stapes head (dashed related to a longitudinal fracture traversing through the arrow), which accounts for the patient’s symptoms EAC (white arrow) Imaging of Temporal Bone Trauma 133

5 What the Surgeon Wants to Know (Table 5)

Table 5 Important checklist for reporting temporal bone trauma What the surgeon wants to know Descriptor Remember Location and direction of • Use mixed classifcation, be aware of pseudo-fractures fracture Otic capsule violation • Look for indirect signs like pneumolabyrinth Ossicular integrity • Compare with normal side for ossicular alignment • Use oblique reformations to visualize the joints and individual ossicles better • Dislocations are more common than ossicular fractures • Incudostapedial dislocation commonest followed by malleo-incudal Facial nerve canal • Look for fracture line running close to the facial canal or subtle enlargement of (does the facial nerve geniculate fossa; if in doubt and clinical symptoms persist, suggest MRI need to be • In acute palsy, a bony fracture fragment indenting on the nerve or loss of the decompressed?) normal canal borders is suspicious for impingement. • Facial nerve canal fracture can occur without any nerve dysfunction or overt impingement of the nerve Tegmen: tympani and • Do not miss → short-term (meningitis, CSF leak) and long-term complications mastoideum (encephalocele) Vascular: carotid canal • ICA → dissection, occlusion, pseudoaneurysm or carotid-cavernous fstula (petrous, cavernous), • Traumatic venous sinus thrombosis venous sinus (transverse, • Suggest CT angio/venography when in doubt sigmoid and jugular bulb)

poral bone trauma. Neuroimaging Clin 24:467–486 Suggested Reading Kwong Y, Yu D, Shah J (2012) Fracture mimics on tem- poral bone CT: a guide for the radiologist. AJR Am J Juliano AF, Ginat DT, Moonis G (2015) Imaging review Roentgenol 199(2):428–434. https://doi.org/10.2214/ of the temporal bone: part II. Traumatic, ­postoperative, AJR.11.8012 and noninfammatory nonneoplastic conditions. Patel A, Groppo E (2010) Management of temporal Radiology 276:655–672 bone trauma. Craniomaxillofac Trauma Reconstr 3: Kennedy TA, Avey GD, Gentry LR (2014) Imaging of tem- 105–113