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HESP632 Medical > Temporal Bone > Flashcards

Temporal Bone Flashcards

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USMLE® Step 1 flashcards
1
Q

Temporal Bone/Skull General overview

A

There are 22 bones in the skull: 8 bones in the cranium and 14 bones in the facial skeleton. The
temporal bone is located on the lateral side of the skull, and is bordered by the mandible, zygomatic, parietal, sphenoid and occipital bones of the skull. Every human has two temporal bones (left and right ear).

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2
Q

Parts of the temporal bone

A

The temporal bone has 4 Major Subdivisions: Squamous division, Mastoid division, Tympanic division, and Petrous division.

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3
Q

Contents of the temporal bone

A
  •   Auditory mechanoreceptors
  •   Vestibular mechanoreceptors
  •   CN V, VII, and VIII
  •   Sigmoid sinus – Allows veins to run in a tortuous course from beneath the temporal bone to the jugular foramen (becomes jugular vein)
  •   Jugular bulb – Dilated part of the internal jugular vein
  •   Middle meningeal artery –  Branch of the carotid artery
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4
Q

Landmarks of the temporal bone

A
  •   Styloid process: Anteroinferior projection of temporal bone; Connects to muscles important for speech production
  •   Temporomandibular joint (TMJ): Joint formed by the connection of the mandible to the temporal bone
  •   Zygomatic process: Long, arching process extending from the inferior portion of the squamous division; articulates with the zygomatic bone.
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5
Q

Mastoid Air Cell System

A

–  Sections of the mastoid process are hallow (beehive)
–  cells can vary in size and number
•  Superior, anterior cells are large and air-filled
•  Inferior cells are smaller and may contain marrow

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6
Q

Incidence of Closed Head Injury

A

•  180-400 per 100,000 •  7.5 million/year, 1.3 million major HI •  2-4 males: 1 female •  peak age: 15-24 years •  peak season: summer •  49% traffic related •  28% falls

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7
Q

Categories of Closed Head Injury

A

•  Fatal
•  Severe:
–  LOC or PTA >24 hrs, &/or cerebral contusion, laceration or intracranial hematoma

•  Moderate:
–  LOC or PTA <24 hrs and >30 min, &/or skull fx

•  Mild:
–  LOC or PTA <30 min, no skull fx

•  Trivial:
–  no LOC or PTA

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8
Q

Pathology of Closed Head Injury

A 
•  Primary mechanisms 
– Contusions or lacerations of the brain 
•  Secondary mechanisms 
– Intracranial hemorrhage 
•  Secondary effects of extracranial events 
– Hypoxia 
•  Delayed effects 
– Degeneration of white matter
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9
Q

Skull Fractures Following with Head Injury

A 
Occur in 10% of head-injured patients
•  28% frontal
•  25% parietal
•  20% occipital
•  12% temporal bone
•  15% basilar skull
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10
Q

…Some More Facts

A
  •   The ear is the most commonly damaged sense organ in closed head injury
  •   30-70% of those with blunt head trauma involve injury to the temporal bone.
  •   40% of patients with head injury and temporal bone trauma report immediate hearing loss as a chief complaint.
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11
Q

Classifications of Trauma to the Temporal Bone

A 
•  Blunt trauma
– without fracture
– with fracture 
•  Penetrating trauma
•  Compressive injuries
•  Thermal trauma
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12
Q

Trauma with Fracture

A

  Most often from blunt trauma
•  Temporal bone fractures
– Longitudinal – Transverse – Oblique – Mixed

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13
Q

Longitudinal Temporal Bone Fracture

A

•  70-90% of temporal bone fx
•  Blow to temporal or parietal region
•  Anatomic course
–  lengthwise through the petrous pyramid
–  squamous portion of the temporal bone to the anterior portion of the petrous apex
–  posterior-superior EAC –  tear TM –  roof of ME
–  usually anterior to labyrinthine capsule
•  Clinical findings
– hearing loss - typically conductive
– EAC: lacerated or collapsed; protruding ossicles
– TM: perforated; bloody otorrhea
– Middle ear: hemotympanum, ossicular displacement, edema

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14
Q

Transverse Temporal Bone Fracture

A

Incidence: 20-30%
•  Blow to occipital or frontal region
•  Anatomic course
–  jugular foramen –  across petrous pyramid –  Through IAC or otic capsule
•  Clinical findings
– SNHL
– Vestibular damage: vertigo with N&V; spontaneous nystagmus
– CNVII damage: 50%
– Frequent hemotympanum behind intact TM when fracture extends to promontory (OW/RW)

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15
Q

Mixed and Oblique Fractures of the Temporal Bone

A

Mixed – Pure longitudinal or transverse are uncommon – 50-75% are mixed

Oblique –  extends between the coronal and axial planes – “Most common”

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16
Q

Microscopic Fractures of the Temporal Bone

A

– Not seen on radiological exam – May be restricted to otic capsule – May explain later SNHL – Can lead to possible meningitis

17
Q

Penetrating Trauma to the Temporal Bone

A

•  Cause
– GSW

•  Extent of injury
– canal laceration, TM perforation, ossicular disruption
– GSW effect depends on mass, velocity and direction of the bullet

18
Q

Trauma without Fracture

A 
Causes
•  Blunt trauma
•  Thermal
•  Foreign body
•  Compressive injuries
•  Blunt head trauma - concussive
•  Barotrauma

Thermal Injuries
•  Frostbite
•  Lightning – Fusion of ossicles – Inner ear injury with SNHL, vertigo, tinnitus, CNVII paralysis

Foreign body
•  Often self-inflicted
•  Minor laceration to inner ear damage

Compressive injuries
•  Causes – Strikes to side of head – Fall on water surface – Blast injuries
•  Damage – TM laceration – Implosion of TM – HF SNHL

19
Q

Hearing Loss as a Complication of CHI

A

Longitudinal fracture
–  predominantly conductive –  resolves over time –  if no resolution, suspect ossicular chain injury

Transverse fracture
–  predominantly SNHL –  possible central auditory deficit –  conductive component secondary to hemotympanum

Mixed and Microscopic
– middle and inner ear may both be damaged

20
Q

CHL in Temporal Bone Injury

A

  Acute
–  EAC: hematoma, debris, blood clot in ME space
–  TM injury
–  ME: CSF or blood
– Ossicular injury
•  Incudostapedial joint separation: 75-92%
•  Dislocation of incus: 58%
•  Fracture of stapedial arch: 30%
•  Fracture of malleus: 11%
•  Fixation of upper ossicular chain: 25%

Delayed onset
–  Stenosis of EAC
–  Ossiclar fixation secondary to fibrous adhesions

21
Q

SNHL in Temporal Bone Injury

A
  •  Transverse fracture - direct damage to inner ear and/or IAC
  •   Longitudinal fracture - 1/3 with HF SNHL, 2º concussive injury
  •   Concussive injuries (more to come)
  •   Little correlation between severity of trauma and degree of loss
22
Q

Concussive Injuries

A

•  Disruption of membranous labyrinth by pressure waves transmitted from intracranial CSF
–  Organ of Corti principle site
–  dislodgment of otoconia
–  secondary degeneration of nerve endings

•  Disruption of the microcirculation of the cochlea
•  Hemorrhage into the cochlea
•  Central damage
–  tearing or stretching of CNVIII

23
Q

Peripheral Vestibular Injury as a Complication of Head Injury

A
  •  BPPV - most common vestibular manifestation; Damage to utricular maccula; Otoconia to SSC; Immediate onset of symptoms
  • PLF (more later)

•  Longitudinal
–  50% positioning or positional vertigo –  Course- resolves in ~ 6 mos –  VNG - often confirms sx - SN, PN –  Rx - vestibular suppressants

•  Transverse
–  Severe vertigo
–  Course: severe 2-4 days, gradual diminution over 2-3 mos
–  VNG: reduced VOR (total), SN away from the affected ear

•  Labyrinthine Concussions
–  positioning or positional vertigo: 20% –  Course: resolution in ~ 6 mos.. –  Cause - dislodged otoconia, edema, hydrops, fistula –  Incidence
•  greatest with parietal and temporal blows
–  VNG: SN, PN and positioning nystagmus

24
Q

Perilymphatic Fistula (PLF)

A

•  Abnormal communication between the labyrinth and ME space that allows
– passage of perilymph into ME space – air into labyrinth or – mixing of perilymph and endolymph
•  Site: OW, RW
•  Mechanisms – explosive – implosive

implosive

Causes of PLF
•  Iatrogenic •  head trauma •  barotrauma •  congenital malformation of inner ear •  increased CSF pressure •  noise trauma •  tumors in middle ear

Symptoms of PLF
•  Balance – Episodic vertigo – Disequilibrium – Ataxia •  Hearing loss – Sudden – Fluctuating or progressive SNHL •  Tinnitus •  Sx improve in a.m.

Diagnosis of PLF
•  Gold standard: visualization of fistula during exploratory tympanotomy
•  Audiometric findings
–  SNHL, unilateral, variable
•  ECochG
–  increased SP/AP amplitude ratio
•  VNG
–  positional or spontaneous nystagmus
•  Platform VNG fistula test
–  Hennebert’s symptom –  Hennebert’s sign
•  Diagnosis dependent on history
– hearing loss, disequilibrium, or vertigo closely following
•  head trauma, rapid pressure changes, straining
•  Can mimic Meniere syndrome
– especially if there is a secondary component of endolymphatic hydrops

Treatment of PLF
•  Initial - medical approach
– bedrest – elevated head – avoidance of situations that increase CSF pressure – stool softeners

Surgical Treatment of PLF
•  When?
– No recovery after bedrest for one week – deteriorating hearing – incapacitating or protracted vertigo
•  How?
– exploratory tympanotomy – tympanomeatal flap – observe RW/OW for direct leak – RW/OW graft

25
Q

Facial Nerve Damage as a Complication of Head Injury

A

•  Longitudinal fracture •  Shearing forces of blunt trauma •  Hematoma in the nerve sheath •  Edema with constriction

26
Q

Treatment of Temporal Bone Fractures

A

Consider symptoms and underlying evidence for anatomical involvement.

HESP632 Medical (6 decks)

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