Temporal Bone Flashcards
Temporal Bone/Skull General overview
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).
Parts of the temporal bone
The temporal bone has 4 Major Subdivisions: Squamous division, Mastoid division, Tympanic division, and Petrous division.
Contents of the temporal bone
- 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
Landmarks of the temporal bone
- 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.
Mastoid Air Cell System
– 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
Incidence of Closed Head Injury
• 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
Categories of Closed Head Injury
• 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
Pathology of Closed Head Injury
• Primary mechanisms – Contusions or lacerations of the brain • Secondary mechanisms – Intracranial hemorrhage • Secondary effects of extracranial events – Hypoxia • Delayed effects – Degeneration of white matter
Skull Fractures Following with Head Injury
Occur in 10% of head-injured patients • 28% frontal • 25% parietal • 20% occipital • 12% temporal bone • 15% basilar skull
…Some More Facts
- 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.
Classifications of Trauma to the Temporal Bone
• Blunt trauma – without fracture – with fracture • Penetrating trauma • Compressive injuries • Thermal trauma
Trauma with Fracture
Most often from blunt trauma
• Temporal bone fractures
– Longitudinal – Transverse – Oblique – Mixed
Longitudinal Temporal Bone Fracture
• 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
Transverse Temporal Bone Fracture
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)
Mixed and Oblique Fractures of the Temporal Bone
Mixed – Pure longitudinal or transverse are uncommon – 50-75% are mixed
Oblique – extends between the coronal and axial planes – “Most common”
Microscopic Fractures of the Temporal Bone
– Not seen on radiological exam – May be restricted to otic capsule – May explain later SNHL – Can lead to possible meningitis
Penetrating Trauma to the Temporal Bone
• Cause
– GSW
• Extent of injury
– canal laceration, TM perforation, ossicular disruption
– GSW effect depends on mass, velocity and direction of the bullet
Trauma without Fracture
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
Hearing Loss as a Complication of CHI
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
CHL in Temporal Bone Injury
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
SNHL in Temporal Bone Injury
- 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
Concussive Injuries
• 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
Peripheral Vestibular Injury as a Complication of Head Injury
- 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
Perilymphatic Fistula (PLF)
• 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
Facial Nerve Damage as a Complication of Head Injury
• Longitudinal fracture • Shearing forces of blunt trauma • Hematoma in the nerve sheath • Edema with constriction
Treatment of Temporal Bone Fractures
Consider symptoms and underlying evidence for anatomical involvement.
