Temporal Bone Trauma What the Radiologist Needs to

Temporal Bone Trauma: What the Radiologist Needs to Know Laura B Eisenmenger, MD Richard H Wiggins III, MD University of Utah Health Sciences Center Salt Lake City, UT e. Ed. E-145

Temporal Bone Trauma: Disclosures • No disclosures 2/43

Temporal Bone Trauma: Objectives • Learn about temporal bone anatomy • Recognize important anatomic variations • Learn the difference between different classification systems • Longitudinal versus transverse • Otic capsule involving versus otic capsule sparing • Petrous and nonpetrous fractures • Recognize when additional reformations or imaging modalities are needed 3/43

Temporal Bone Trauma: Outline Temporal Bone Trauma: What the Radiologist Needs to Know • Introduction • Temporal bone anatomy • Variant anatomy • Fracture classification systems • Longitudinal versus transfer • Otic capsule violating versus sparing • Petrous versus non-petrous apex • Occult fractures • Fracture mimics • Summary 4/43

Temporal Bone Trauma: Introduction • Temporal bone anatomy is complex with many critical structures and functions • Injury to the temporal bone can cause serious vascular, nervous, and structural abnormalities • Complications of temporal bone trauma can include conductive hearing loss, sensorineural hearing loss, vertigo, perilymphatic fistulas, cerebrospinal fluid (CSF) leaks, and facial nerve paralysis • Proper identification of temporal bone injuries can direct treatment and help prevent complications 5/43

Temporal Bone Trauma: Normal anatomy Temporal bone anatomy • Major components of temporal bone • • External auditory canal (EAC) Middle ear (ME) Inner ear (IE) Petrous apex (PA) Internal auditory canal (IAC) Facial nerve (CN 7) Petrous internal carotid artery (ICA) 6/43

Temporal Bone Trauma: Normal anatomy Temporal bone anatomy • External ear: • Auricle • External auditory canal : • Tympanic bone medially, fibrocartilage laterally • Medial border is tympanic membrane • Nodal drainage to parotid chain 7/43

Temporal Bone Trauma: Normal anatomy Temporal bone anatomy • 5 osseous parts of the temporal bone: • Squamous: Forms lateral wall of middle cranial fossa • Mastoid: Aerated posterolateral temporal bone • Petrous: Pyramidal shaped medial portion containing inner ear, internal auditory canal, and petrous apex • Tympanic: U-shaped bone forming bony external auditory canal • Styloid: Forms styloid process after birth 8/43

Temporal Bone Trauma: Normal anatomy Temporal bone anatomy • Middle ear • Epitympanum: Middle ear above line from scutal tip to tympanic CN 7 • Tegmen tympani: Roof of middle ear cavity • Prussak space: Lateral epitympanic recess • Mesotympanum: Middle ear proper • Posterior wall: Facial nerve recess, pyramidal eminence, sinus tympani • Medial wall: Lateral semicircular canal, tympanic segment CN 7, oval & round window • Hypotympanum: Shallow region in floor of middle ear 9/43

Temporal Bone Trauma: Normal anatomy Temporal bone anatomy • Mastoid sinus: 4 key structures • Aditus ad antrum: Connects epitympanum to mastoid antrum • Mastoid antrum: Large, central mastoid air cell • Körner septum: Part of petrosquamosal suture running posterolaterally through mastoid air cells • Tegmen mastoideum: Roof of mastoid air cells 10/43

Temporal Bone Trauma: Normal anatomy Temporal bone anatomy • Inner ear: • Bony labyrinth: Bone that confines cochlear, vestibule, & semicircular canals • Cochlea: ~ 2. 5 turns with central modiolus and 3 spiral chambers (scala tympani, scala vestibuli, & scala media) • Semicircular canals (SCCs): Superior (S), lateral (L), & posterior (P) • SSCC: Projects cephalad; bony ridge over SSCC is called arcuate eminence • LSCC: Projects into middle ear; tympanic CN 7 on underside • PSCC: Projects posteriorly parallel to petrous ridge 11/43

Temporal Bone Trauma: Normal anatomy Temporal bone anatomy • Inner ear: • Perilymphatic spaces • Perilymph is the fluid within bony labyrinth that surrounds endolymphcontaining membranous labyrinth structures • Perilymphatic spaces include the area in vestibule surrounding utricle & saccule, in semicircular canals around semicircular ducts, and within scala tympani & vestibuli of cochlea • Membranous labyrinth/endolymphatic spaces • Endolymph is the fluid within structures of membranous labyrinth • Includes the vestibule (utricle & saccule), semicircular ducts, scala media (cochlear duct), and endolymphatic duct & sac 12/43

Temporal Bone Trauma: Normal anatomy Temporal bone anatomy • Intratemporal facial nerve: • CN 7 segments: IAC, labyrinthine, tympanic, mastoid segments • Anterior genu: the geniculate ganglion • Posterior genu: tympanic segment bends inferiorly to become mastoid segment • Stylomastoid foramen: CN 7 exits skull base • Petrous internal carotid artery: C 2 segment • Vertical segment: Rises to genu beneath cochlea • Horizontal segment: Projects anteromedially turning cephalad as the precavernous & cavernous ICA • Petrous apex: Anteromedial to inner ear 13/43

Temporal Bone Trauma: Variant anatomy Temporal bone variant anatomy • Aberrant carotid artery • Tubular lesion crossing middle ear from posterior to anterior • Congenital vascular anomaly resulting from failure of formation of extracranial ICA with arterial collateral pathway • Enlarged inferior tympanic canaliculus important observation • Caution: Do not mistake for glomus tympanicum paraganglioma 14/43 Axial CT

Temporal Bone Trauma: Variant anatomy Temporal bone variant anatomy • High riding jugular vein/bulb (JB) • Superior aspect of JB extends above floor of IAC with no middle ear connection • High JB is more commonly seen with poorly aerated mastoid air cells • If dehiscence into middle ear present, use "dehiscent JB" not "high JB" to describe 15/43 Axial CT

Temporal Bone Trauma: Variant anatomy Temporal bone variant anatomy • Ectopic facial nerve • Facial nerve can have a number of variations in its course • Facial nerve should be traced throughout its course on every exam • Caution: facial nerve location must be evaluated while evaluating for fractures or facial nerve injury may be missed Coronal CT Ectopic facial overlying atretic oval window 16/43

Temporal Bone Trauma: Fracture classification systems • Multiple fracture classification systems have been proposed in the past: • Traditional classification: Longitudinal versus transverse fractures • Otic capsule violating versus otic capsule sparing • Petrous versus nonpetrous fractures 17/43

Temporal Bone Trauma: Longitudinal versus transverse Traditional classification • Traditional system indicates the relationship of the fracture line with the long axis of the petrous portion of the temporal bone • Factures are classified as longitudinal versus transverse • 70 -90% of fractures are longitudinal and 10 -30% are transverse 18/43

Temporal Bone Trauma: Longitudinal versus transverse Longitudinal fractures • Fracture line parallel to the long axis of the petrous bone • Fracture line typically runs through the petrous apex • Involvement of the otic capsule is rare • Most common complications: ossicle injury, tympanic membrane rupture, hemotympanum, conductive hearing loss 19/43

Temporal Bone Trauma: Longitudinal versus transverse Transverse fractures • Fracture line perpendicular to the long axis of the petrous bone • Line of force extending anterior to posterior, resulting from frontal of occipital region trauma • Sensorineural hearing loss and facial paralysis are more common 20/43

Temporal Bone Trauma: Longitudinal versus transverse Axial CT Transverse fracture extending perpendicular to the petrous apex 21/43 Axial CT Longitudinal fracture extending parallel to the petrous apex

Temporal Bone Trauma: Longitudinal versus transverse Mixed fractures • Complex fractures are limited in the traditional classification system based primarily on cadaveric studies and not representative of many traumas • New classification was proposed with multidetector CT • Mixed fractures include both longitudinal and transverse elements • More frequent involvement of the otic capsule and ossicles 22/43 Axial CT Mixed temporal bone fracture with transverse and longitudinal components

Temporal Bone Trauma: Otic capsule classification • Brodie et al. , proposed a system based on otic capsule involvement or sparing • Otic capsule violating fractures course through the labyrinth: the cochlea, vestibule and/or semicircular canals • Otic capsule violating fractures are more commonly associated with sensorineural hearing loss, cerebrospinal fluid otorrhea, and facial nerve injury • Otic capsule sparing fractures are more commonly associated with intracranial injuries 23/43

Temporal Bone Trauma: Otic capsule classification • Sensorineural hearing loss can result from fracture/injury to the cochlea, cochlear nerve, or cochlear nuclei • When no definitive fracture is present in the setting of sensorineural hearing loss, cochlear contusion is possible • MR can be used to better assess the cochlear nerve if clinically indicated 24/43

Temporal Bone Trauma: Otic capsule classification • Vertigo frequently occurs after temporal bone trauma and may be secondary to injury to the vestibular apparatus, the vestibular nerve, the vestibular aqueduct or the semicircular canals • Vertigo without fracture can be seen in the setting of vestibular concussion • Benign paroxysmal positional vertigo is the most common form of dysequilibrium after head injury, usually resolving in 6 -12 months • Perilymphatic fistulas, labyrinthine concussions, or otolith detachment are also possible causes of posttraumatic vertigo 25/43

Temporal Bone Trauma: Otic capsule violating fractures Axial CT Axial. CT CTCT Axial Fracture extending through the vestibule and semicircular canals 26/43 Fracture extending into the basal turn of cochlea

Temporal Bone Trauma: Otic capsule sparing fracture Axial CT Depressed squamosal portion of the temporal bone fracture 27/43 Axial CT Underlying intracranial hemorrhage

Temporal Bone Trauma: Petrous versus nonpetrous classification • Ishman and Freidland proposed a system based on petrous versus nonpetrous fractures • Petrous fractures extend into the petrous apex or otic capsule • Petrous fractures are more likely complicated by cerebrospinal fluid leak or facial nerve injury • Nonpetrous fracture does not involve the petrous apex or otic capsule but may extend into the middle ear or mastoid • Nonpetrous fractures are more likely to cause conductive hearing loss 28/43

Temporal Bone Trauma: Injuries not to miss: Ossicles • Ossicle dislocation or fracture: conductive hearing loss most commonly results from ossicular injury in the setting of trauma • Axial imaging has traditionally been viewed as the primary plane to view ossicular dislocation with typically described dislocation types including incudomalleolar joint separation, incudostapedial joint separation, dislocation of the incus, dislocation of the malleoincudal complex , and stapediovestibular dislocation • All planes provide additional information such as coronal imaging which may be even better to view subtle malleoincudal dislocation with the “broken heart” sign • Fractures of the ossicles most commonly involve the poorly supported long process of the incus followed by the crura of the stapes 29/43

Temporal Bone Trauma: Injuries not to miss Ossicle injury Axial CT Normal alignment of the ossicles 30/43 Malleoincudal dislocation with widening of the joint space with longitudinal fracture through the mastoid and associated joint fluid

Temporal Bone Trauma: Injuries not to miss: Carotid artery • The temporal bone contains the petrous portion of the internal carotid artery • Resnick and colleagues found that 24% of patients had fractures involving the carotid canal with 11% of whom had vascular complications • CTA of the head should be performed to evaluate for vascular injury if there is any involvement of the carotid canal • Complications from carotid artery injury include arterial dissection, pseudoaneurysm, arteriovenous fistula, complete transection, and occlusion 31/43

Temporal Bone Trauma: Injuries not to miss Carotid canal fracture Axial CTCT Fracture seen extending across the carotid canal. CTA should be performed to evaluate the carotid artery for injury 32/43 Air seen surrounding the petrous portion of the carotid artery in setting of fracture

Temporal Bone Trauma: Injuries not to miss: Facial nerve • The facial is injured in approximately 7% of patients with a temporal bone fracture • The entire facial nerve course should be evaluated for injury as direct visualization of the facial nerve itself on CT is limited • Immediate posttraumatic paralysis is frequently indicative of transection of the nerve or direction compression • Delayed onset paralysis is more indicative of edema, swelling, or worsening hematoma causing compression on an intact nerve 33/43

Temporal Bone Trauma: Injuries not to miss: Foreign bodies • Foreign bodies provide an additional component of complexity • Foreign bodies also can point to injury mechanism and draw your attention to other possible injuries ***Radiologist should describe any possible injuries related to the foreign body to relay issues the surgeon may encounter while removing the object Axial CT Nail extending through the middle ear with the tip extending to the basal turn of the cochlea. A small cochlear leak was found at surgery. Ossicles and facial nerve were not injured. 34/43

Temporal Bone Trauma: Injuries not to miss: Occult fractures • Temporal bone fractures may not be seen on additional studies but secondary signs can help point towards a possible fracture such as: • • • Opacification of the mastoid air cells Opacification of the middle ear Opacification of the external ear Pneumocephalus adjacent to the temporal bone Extraaxial fluid collection or intracranial injury Air in the glenoid fossa of the TMJ • Additional imaging can be obtained such as a dedicated temporal bone reformatted images or temporal bone CT • MR can be obtained to better evaluate nerves and the otic capsule specifically 35/43

Temporal Bone Trauma: Fracture mimics • Temporal bone anatomy is complex • Given the complexity, many normal canals/sutures as well as common anatomic variants can mimic fractures including but not limited to the following: • • • Venous channels Inferior petrosal veins Subarcuate canal Endolymphatic duct and sac Cochlear duct Facial nerve 36/43

Temporal Bone Trauma: Fracture mimics Axial CT Normal endolymphatic sac Normal cochlear duct 37/43

Temporal Bone Trauma: Classification systems Which classification system to use • There is some disagreement in the literature regarding which classification system is best regarding temporal bone fractures • Multiple studies have demonstrated that the otic capsule system may have the best guidance to help predict clinical outcomes and direct surgical planning • Dahiya et al demonstrated otic capsule violating fractures are approximately twice as likely to develop facial paralysis, four times as likely to develop cerebrospinal leak, seven times as likely to experience hearing loss, and more likely to sustain intracranial complications 38/43

Temporal Bone Trauma: Classification systems Which classification system to use • The traditional system of longitudinal and transverse fractures is familiar with a large number of clinicians and can give physicians a conceptual idea of the fracture pattern ***the most valuable description may be to simply describe the fractures and the structures they involve to provide the clinician with all of the relevant structures involved 39/43

Temporal Bone Trauma: Summary • Temporal bone anatomy is complex with many critical structures and functions • Injury to the temporal bone can cause serious vascular, nervous, and structural injuries • Multiple classifications systems have been proposed, but simple accurate description of injured temporal bone structures may provide the most useful information to the clinician • Proper identification of temporal bone injuries can direct treatment and help prevent complications 40/43

Temporal Bone Trauma: Outline Temporal Bone Trauma: What the Radiologist Needs to Know • Introduction • Temporal bone anatomy • Variant anatomy • Fracture classification systems • Longitudinal versus transfer • Otic capsule violating versus sparing • Petrous versus non-petrous apex • Occult fractures • Fracture mimics • Summary 41/43

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Temporal Bone Trauma: What the Radiologist Needs to Know Laura B Eisenmenger, MD Richard H Wiggins III, MD University of Utah Health Sciences Center Salt Lake City, UT