Image Appraisal Head Trauma

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Image AppraisalHead Trauma

• Karen McBean

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Mechanism

• blow to the skull results in compression injury
  to the adjacent brain (coup) and stretching on
  the opposite side (contrecoup). This may result
  in contusion, shearing injuries and rupture of
  intraaxial or extra-axial vessels, leading to
  haemorrhage.

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Types of Skull Fracture

• Types of skull fracture
• Linear- from the point of impact along lines of
  anatomical weakness (eg diastasis of suture
• fusion lines).
• frontal fracture (eg head-on RTA) often radiates
  into anterior cranial fossa
• temporal fracture (eg blow to side of head) often
  radiates into middle cranial fossa
• occipital fracture (eg backwards fall) often
  radiates into posterior cranial fossa
• Radiating- outwards from the point of impact
• Spider's web- radiating lines connected by
  concentric fracture rings

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Types of Skull Fractures

• Depressed- where fragments are driven inwards
• Hinge- passing across the base of the skull
  (motor cyclist or blow to chin)
• Ring- encircling the hole through which the
  spinal cord passes downwards (foramen magnum).
• Due to a fall onto the feet or onto the top of
  the head
• Contre-coup- a backwards fall, striking the back
  of the head (coup) may also cause fracture of
• the thin layer of bone over the roof of the
  orbits opposite the point of impact (contre-coup)
  due
• to suction forces transmitted through the brain
  tissue.

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Plain films

• Absence of fracture does not exclude significant
  intercranial injury so plain films are not the
  imaging modality of choice

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Plain Films

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Plain Films

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Skull trauma

• Cerebral contusion bleeding may occur
• acute hemorrhage hyperdense surrounding edema
• May not occur until hours after the trauma
• NAD, will need to be followed up if patients
  condition deteriorates
• Epidural, subdural, subarachnoid

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Assessment

• CT is a vital tool in the assessment of patients
  with serious head injury,
• It remains the investigation of choice even
  following the advent of MRI, due both to the ease
  of monitoring of injured patients and the better
  demonstration of fresh bleeding and bony injury.

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CT head interpretation

• Scout image
• Plain film radiography
• May show pathology fracture, soft tissue
  pathology
• Annotated scout improves understanding of cross
  sectional slices

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CT head interpretation

• Slices skull base to vertex
• Patient supine , view from feet

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Search patterns - Skull

• Size normal proportions
• Shape oval to round (adult)
• Symmetry generally symmetrical
• Mineralisation lytic or sclerotic lesions
• Bone windowing

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Search Patterns Intracranial contents

• Symmetry marked tendency to symmetry
• eg falx cerebri deviation should be further
  evaluated
• Midline shift
• Proportional - ventricles and sulci

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Search Patterns Intracranial contents

• Localised area of altered density
• Presence of mass lesion
• CSF - black
• Recent haemorrhage and haematoma appear white

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Search Patterns Intracranial contents

• Grey/white differentiation
• grey matter 40HU
• white matter 30HU (fatty myelin)
• pathological changes eg oedema
• white matter exaggerate grey/white
• grey matter - featureless

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Blood Brain Barrier

• Maintains homeostasis of the neuronal environment
• Tight capillary junctions semi permeable
  membrane preventing passage of molecules into the
  extra vascular space
• If damaged, contrast will leak into this space
  intra axial tumors
• Delay scan

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IV contrast

• Vascular many unenhanced
• Increases local absorption coefficient
• Normal cerebral tissue does not enhance due to
  BBB
• Extra axial tissue does enhance
• Eg anterior pituitary gland, meningioma

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IV contrast

• Enable lesion detection
• Most lesions demonstrated to some extent on plain
  mass effect, density variation
• Some isodense or occult (eg CPA)
• Characterisation of a lesion
• Narrows differential diagnosis
• Seldom used dementia, acute CVA, trauma

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Artefacts

• Technical ring
• Patient motion, less with shorter scanning times
• Beam hardening eg posterior fossa
• Metal surgical clips, gunshot fragments
• amalgam

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CT bone window

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Anatomy

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Trauma

• Stages
• Hyperacute - lt 24 hours
• Acute haematoma 1-3 days
• Early subacute 3-7days
• Late subacute 7 14 days
• Chronic gt 14 days

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Epidural Haemotoma

• arise between the inner table of the skull and
  the dura
• develop from injury to the middle meningeal
  artery or one of its branches, and therefore are
  usually temporoparietal in location.
• temporal bone fracture is often the cause, but is
  not essential.
• The expanding haematoma strips the dura from the
  skull this attachment is quite strong such that
  the haematoma is confined, giving rise to its
  characteristic biconvex shape
• a well defined margin.

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Epidural Hematoma

• Blunt trauma at risk
• LOC hemiparesis, headache, dilated pupils,
  increased ICP
• Appears biconvex in shape, displacing brain,
  smooth,
• Noncontrast CT
• Closed vs compound fracture- infection

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SubArachnoid Haemorrhage

• Escape of blood into the subarachnoid space
• the patient may collapse and hit their head as a
  result of a bleed and the
• history (from the patient or a witness) is
  important.

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SubArachnoid Haemorrhage

• Often ruptured Berry aneurysm, arteriovenous
  malformation (AVM)
• Headaches
• Non contrast CT
• High density in the subarachnoid spaces, basilar
  cisterns

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Treatment

• Need to prevent rebleeding and hydrocephalus
• Interventional techniques

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Subdural Haemotoma

• Collection of venous blood between the dura mater
  and arachnoid mater
• Seldom associated with a skull fracture
• Usually a result of head hitting an immoveable
  object
• Symptoms may not arise immediately
• severe consequences due to mass effect, requiring
  urgent surgery

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Subdural Haemotoma

• a crescentic appearance and a more irregular
  inner margin
• May spread along the entire convexity of the
  hemisphere
• Marked displacement of brain tissue
• Acute stage hyperdense
• Subacute isodense
• Chronic - hypodense

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Subdural Haemotoma

• These arise between the dura and arachnoid, often
  from ruptured veins crossing this potential
  space. The space enlarges as the brain atrophies
  and so subdural haematomas are more common in the
  elderly
• Drained through a burr hole

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Acute SDH

• Acute up to 48 hours hyperdense
• Right sided subdural
• Extends into interhemispheric fissure anteriorly
• Compression of the body of the right lateral
  ventricle
• Soft tissue swelling

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• Subacute isodense
• Extensive midline shift
• 5 of head trauma patients

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• Subacute -48 hours to one week
• isodense
• Excellent image quality

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• Chronic 7 to 10 days
• hypodense
• Crescenteric low density collection
• Associated midline shift

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• Same patient
• Dilated opposite lateral ventricle
• Midline shift distorts the foramen of Munro
  causing obstruction

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Complications of Head Injury

• Intracranial hemorrhage
• Brain swelling (cerebral oedema)
• Raised intracranial pressure (raised ICP)
• Meningitis and brain abscess
• Post traumatic epilepsy

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