Temporal Bone Trauma: Normal anatomy

Temporal Bone Trauma: What the Radiologist Needs to

KnowLaura B Eisenmenger, MD

Richard H Wiggins III, MD

University of Utah Health Sciences CenterSalt Lake City, UT

eEdE-145

Disclosures• No disclosures

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Temporal Bone Trauma: Disclosures

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

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Temporal Bone Trauma: Objectives

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

Temporal Bone Trauma: Outline

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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

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Temporal Bone Trauma: Introduction

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 (CN7)• Petrous internal carotid artery

(ICA)

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Temporal Bone Trauma: Normal anatomy

Temporal bone anatomy• External ear:• Auricle• External auditory canal

• External auditory canal :• Tympanic bone medially,

fibrocartilage laterally• Medial border is tympanic

membrane• Nodal drainage to parotid chain

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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

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Temporal bone anatomy• Middle ear

• Epitympanum: Middle ear above line from scutal tip to tympanic CN7

• 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 CN7, oval & round window

• Hypotympanum: Shallow region in floor of middle ear

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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

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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 CN7 on underside• PSCC: Projects posteriorly parallel to

petrous ridge 11/43


Temporal bone anatomy• Inner ear: • Perilymphatic spaces

• Perilymph is the fluid within bony labyrinth that surrounds endolymph-containing 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 & sac12/43


Temporal bone anatomy• Intratemporal facial nerve:

• CN7 segments: IAC, labyrinthine, tympanic, mastoid segments

• Anterior genu: the geniculate ganglion • Posterior genu: tympanic segment bends

inferiorly to become mastoid segment• Stylomastoid foramen: CN7 exits skull

base

• Petrous internal carotid artery: C2 segment• Vertical segment: Rises to genu beneath

cochlea• Horizontal segment: Projects

anteromedially turning cephalad as the precavernous & cavernous ICA

• Petrous apex: Anteromedial to inner ear13/43


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

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Temporal Bone Trauma: Variant anatomy

Axial CT


• 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

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Axial CTAxial CT


• 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 16/43


Coronal CT

Ectopic facial overlying atretic oval window

Coronal CT

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

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Temporal Bone Trauma: Fracture classification

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

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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

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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

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Longitudinal versus transverse

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Axial CT

Longitudinal fracture extending parallel to the petrous apex

Axial CT

Transverse fracture extending perpendicular to the petrous apex

Axial CTAxial CT

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

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Mixed temporal bone fracture with transverse and longitudinal components

Axial CT

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

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Temporal Bone Trauma: Otic capsule

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

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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

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Otic capsule violating fractures

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Axial CT

Fracture extending into the basal turn of cochlea

Axial CT Axial CT

Fracture extending through the vestibule and semicircular canals

Axial CTAxial CT

Otic capsule sparing fracture

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Underlying intracranial hemorrhageDepressed squamosal portion of the temporal bone fracture

Axial CTAxial CT

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

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Temporal Bone Trauma: Petrous versus nonpetrous

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

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Temporal Bone Trauma: Injuries not to miss

Ossicle injury

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Malleoincudal dislocation with widening of the joint space with longitudinal fracture through the mastoid and associated joint fluid

Normal alignment of the ossicles

Axial CTAxial CT

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

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Carotid canal fracture

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Air seen surrounding the petrous portion of the carotid artery in setting of fracture

Axial CT Axial CT

Fracture seen extending across the carotid canal. CTA should be performed to evaluate the carotid artery for injury

Axial CTAxial CT

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

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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

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Axial CTNail 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.

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

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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

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Temporal Bone Trauma: Fracture mimics

Fracture mimics

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Temporal Bone Trauma: Fracture mimics

Normal cochlear ductNormal endolymphatic sac

Axial CTAxial CT

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

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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

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Temporal Bone Trauma: Classification systems

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

Temporal Bone Trauma: Summary

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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

Temporal Bone Trauma: Outline

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Multidetector CT in the Emergency Department. RadioGraphics 2011; 31:1741–1755.• 2. Dahiya R, Keller JD, Litofsky NS, Bankey PE, Bonassar LJ, Megerian CA. Temporal bone fractures: otic capsule sparing versus otic capsule violating

clinical and radiographic considerations. J Trauma1999;47(6):1079–1083.• 3. Brodie HA, Thompson TC. Management of complications from 820 temporal bone fractures. Am J Otol 1997;18(2):188–197.• 4. Nosan DK, Benecke JE Jr, Murr AH. Current perspective on temporal bone trauma. Otolaryngol Head Neck Surg 1997;117(1):67–71.• 5. Ishman SL, Friedland DR. Temporal bone fractures: traditional classification and clinical relevance. Laryngoscope 2004;114(10):1734–1741.• 6. Gurdjian ES, Lissner HR. Deformations of the skull in head injury studied by the stresscoat technique: quantitative determinations. Surg Gynecol

Obstet 1946;83:219–233.• 7. Swartz JD. Trauma. In: Swartz JD, Harnsberger HR, eds. Imaging of the temporal bone. 3rd ed. New York, NY: Thieme, 1997; 318–344.• 8. Avrahami E, Chen Z, Solomon A. Modern high resolution computed tomography (CT) diagnosis of longitudinal fractures of the petrous bone.

Neuroradiology 1988;30(2):166–168.• 9. Griffin JE, Altenau MM, Schaefer SD. Bilateral longitudinal temporal bone fractures: a retrospective review of seventeen cases. Laryngoscope

1979;89(9• pt 1):1432–1435.• 10. Patay Z, Louryan S, Balériaux D. Early complications of petrous bone fractures. Riv Neuroradiol 1995;8:855–866.• 11. Cannon CR, Jahrsdoerfer RA. Temporal bone fractures: review of 90 cases. Arch Otolaryngol 1983; 109(5):285–288.• 12. Schubiger O, Valavanis A, Stuckmann G, Antonucci F. Temporal bone fractures and their complications. Examination with high resolution CT.

Neuroradiology 1986;28(2):93–99.• 13. Fisch U. Facial paralysis in fractures of the petrous bone. Laryngoscope 1974;84(12):2141–2154.• 14. Harker LA, McCabe BF. Temporal bone fractures and facial nerve injury. Otolaryngol Clin North Am 1974;7(2):425–431.• 15. Travis LW, Stalnaker RL, Melvin JW. Impact trauma of the human temporal bone. J Trauma 1977;17(10): 761–766.• 16. Little SC, Kesser BW. Radiographic classification of temporal bone fractures: clinical predictability using a new system. Arch Otolaryngol Head Neck

Surg• 2006;132(12):1300–1304.• 17. Meriot P, Veillon F, Garcia JF, et al. CT appearances of ossicular injuries. RadioGraphics 1997;17(6): 1445–1454.• 18. Resnick DK, Subach BR, Marion DW. The significance of carotid canal involvement in basilar cranial fracture. Neurosurgery 1997;40(6):1177–1181.

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Temporal Bone Trauma: What the Radiologist Needs to

KnowLaura B Eisenmenger, MD

Richard H Wiggins III, MD

University of Utah Health Sciences CenterSalt Lake City, UT

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Temporal Bone Trauma: Normal anatomy