Transcript Temporal Bone Trauma: Normal anatomy

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
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Temporal Bone Trauma: Disclosures
Disclosures
• No disclosures
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Temporal Bone Trauma: Objectives
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: 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
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Temporal Bone Trauma: Introduction
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: Normal anatomy
Temporal bone anatomy
• Major components of temporal
bone
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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 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
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Temporal Bone Trauma: Normal anatomy
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 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
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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 CN7 on underside
• PSCC: Projects posteriorly parallel to
petrous ridge
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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
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Temporal Bone Trauma: Normal anatomy
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
ear
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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
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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
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Axial
CT
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
Coronal CT
Ectopic facial overlying atretic oval window
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Temporal Bone Trauma: Fracture classification
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: 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
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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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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
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Temporal Bone Trauma: Longitudinal versus transverse
Longitudinal versus transverse
Axial
CT
Axial CT
Transverse fracture extending
perpendicular to the petrous apex 21/43
Axial
CT
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
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Axial CT
Mixed temporal bone fracture
with transverse and longitudinal
components
Temporal Bone Trauma: Otic capsule
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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Temporal Bone Trauma: Otic capsule
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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Temporal Bone Trauma: Otic capsule
Otic capsule violating fractures
Axial
CT
Axial CT
Axial
AxialCT
CTCT
Axial
Fracture extending through the vestibule
and semicircular canals
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Fracture extending into the basal turn
of cochlea
Temporal Bone Trauma: Otic capsule
Otic capsule sparing fracture
Axial CT
Axial CT
Depressed squamosal portion of the
temporal bone fracture
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Underlying intracranial hemorrhage
Temporal Bone Trauma: Petrous versus nonpetrous
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: Injuries not to miss
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
Axial CT
Axial CT
Normal alignment of the ossicles
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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
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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Temporal Bone Trauma: Injuries not to miss
Carotid canal fracture
Axial
Axial CTCT
Axial
Axial CTCT
Fracture seen extending across the carotid
canal. CTA should be performed to evaluate
the carotid artery for injury
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Air seen surrounding the petrous
portion of the carotid artery in setting
of fracture
Temporal Bone Trauma: Injuries not to miss
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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Temporal Bone Trauma: Injuries not to miss
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.
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Temporal Bone Trauma: Injuries not to miss
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:
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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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Temporal Bone Trauma: Fracture mimics
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:
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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
Axial CT
Axial CT
Normal endolymphatic sac
Normal cochlear duct
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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
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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: Summary
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
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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
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References
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1. Julio O. Zayas, MD, Yara Z. Feliciano, MD, Celene R. Hadley, MD, Angel A. Gomez, MD, Jorge A. Vidal, MD. Temporal Bone Trauma and the Role of Multidetector CT in the Emergency
Department. RadioGraphics 2011; 31:1741–1755.
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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.
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3. Brodie HA, Thompson TC. Management of complications from 820 temporal bone fractures. Am J Otol 1997;18(2):188–197.
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4. Nosan DK, Benecke JE Jr, Murr AH. Current perspective on temporal bone trauma. Otolaryngol Head Neck Surg 1997;117(1):67–71.
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5. Ishman SL, Friedland DR. Temporal bone fractures: traditional classification and clinical relevance. Laryngoscope 2004;114(10):1734–1741.
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13. Fisch U. Facial paralysis in fractures of the petrous bone. Laryngoscope 1974;84(12):2141–2154.
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14. Harker LA, McCabe BF. Temporal bone fractures and facial nerve injury. Otolaryngol Clin North Am 1974;7(2):425–431.
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15. Travis LW, Stalnaker RL, Melvin JW. Impact trauma of the human temporal bone. J Trauma 1977;17(10): 761–766.
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17. Meriot P, Veillon F, Garcia JF, et al. CT appearances of ossicular injuries. RadioGraphics 1997;17(6): 1445–1454.
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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 Know
Laura B Eisenmenger, MD
Richard H Wiggins III, MD
University of Utah Health Sciences Center
Salt Lake City, UT