P year‎ > ‎Neurology‎ > ‎

12.10.19 Head injury

Mechanisms
  • Penetrating
    • Generally minimal brain injury
      • e.g. Pool cue boy
  • Crush
    • Tends to damage base of skull
    • => Cranial nerve injury
  • Acceleration/Deceleration
    • Rotational forces magnify the effect
    • Damage to olfactory nerve
    • Damage to pituitary stalk
      • => e.g. diabetes insipidus
  • Missile
    • Damage proportional to velocity squared

Secondary damage
  • Raised ICP
    • Normal ICP ~10 mmHg
    • CPP = BP - ICP = Normally 100 mmHg
    • CPP <60 mmHg => Unconscious
  • Fits
    • Especially common in children
    • Causes hypoxic injury
      • Stop breathing
      • Raised cerebral oxygen demands
    • Easy to miss if sedated and intubated!
      • Consider prophylactic meds
  • Infection
    • e.g. Gardener scythe man
    • Check for dura breech
      • Loss of CSF

Cushing's Sign

  • Traditionally hypertension, bradycardia, and irregular respiration
  • Alternatively widened pulse pressure, irregular respiration, and bradycardia
    • Elevated systolic BP and a either decreased or normal diastolic BP
  • Watch out for:
    • Hypertension
    • Bradycardia
  • e.g. Kid kicked in the head

Indications for CT scan

  • GCS < 13 when first assessed in emergency department
  • GCS < 15 when assessed in emergency department 2 hours after the injury
  • Suspected open or depressed skull fracture
  • Sign of fracture at skull base
    • Haemotympanum
    • ‘Panda’ eyes
    • Cerebrospinal fluid leakage from ears or nose
    • Battle’s sign
  • Post-traumatic seizure
  • Focal neurological deficit
  • > 1 episode of vomiting
  • Amnesia of events > 30 minutes before impact

Indications for admission

  • New, clinically significant abnormalities on imaging
  • Not returned to GCS 15 after imaging, regardless of the imaging results
  • Criteria for CT scanning fulfilled, but scan not done within appropriate period, either because CT not available or because patient not sufficiently co-operative to allow scanning
  • Continuing worrying signs
    • For example, persistent vomiting, severe headaches
  • Other sources of concern
    • For example, drug or alcohol intoxication, other injuries, shock, suspected non-accidental injury, meningism, cerebrospinal fluid leak

Indications for review during observation period
  • Agitation or abnormal behaviour developed
  • GCS dropped by 1 point and lasted for at least 30 minutes
    • Give greater weight to a drop of 1 point in the motor response score
  • Any drop of 3 or more points in the eye-opening or verbal response scores, or 2 or more points in the motor response score
  • Severe or increasing headache developed or persistent vomiting
  • New or evolving neurological symptoms or signs, such as pupil inequality or asymmetry of limb or facial movement

Discharge
  • In general, only discharge when certain there is somebody suitable at home to supervise the patient

CSF Leakage

  • Look at nose and ears
  • If unsure what it is, check [glucose]
    • Distinguishes nasal CSF from snot


Wallerian degeneration
  • Results when a nerve fiber is cut or crushed
  • Distal axon degenerates
    • Known as anterograde or orthograde degeneration
  • Due to a failure to deliver sufficient quantities of the essential axonal protein NMNAT2
  • Occurs after axonal injury in both the PNS and CNS
  • Usually begins within 24–36 hours of a lesion
    • Axonal skeleton disintegrates
    • Axonal membrane breaks apart
    • Axonal degeneration is followed by degradation of the myelin sheath and infiltration by macrophages
  • Neurolemma does not degenerate and remains as a hollow tube
    • Sprouts are sent out towards those tubes and these sprouts are attracted by growth factors produced by Schwann cells in the tubes
    • If a sprout reaches the tube, it grows into it and advances about 1 mm per day, eventually reaching and reinnervating the target tissue
    • If the sprouts cannot reach the tube, for instance because the gap is too wide or scar tissue has formed, surgery can help to guide the sprouts into the tubes


Types of peripheral nerve injury

  • Neurapraxia (Class I)
    • Temporary interruption of conduction without loss of axonal continuity
    • Physiologic block
    • Endoneurium, perineurium, and the epineurium are intact
    • There is no wallerian degeneration
    • Conduction is intact in the distal segment and proximal segment, but no conduction occurs across the area of injury
    • Recovery of nerve conduction deficit is full,and requires days to weeks
    • EMG shows lack of fibrillation potentials (FP) and positive sharp waves
  • Axonotmesis (Class II)
    • Loss of the relative continuity of the axon and its covering of myelin, but preservation of the connective tissue framework of the nerve
    • Wallerian degeneration occurs below to the site of injury
    • There are sensory and motor deficits distal to the site of lesion
    • There is no nerve conduction distal to the site of injury (3 to 4 days after injury)
    • EMG shows fibrillation potentials (FP),and positive sharp waves (2 to 3 weeks postinjury)
    • Axonal regeneration occurs and recovery is possible without surgical treatment
    • Sometimes surgical intervention because of scar tissue formation is required
  • Neurotmesis (Class III)
    • Total severance or disruption of the entire nerve fiber
    • Wallerian degeneration occurs below to the site of injury
    • There is connective tissue lesion that may be partial or complete
    • Sensory-motor problems and autonomic function defect are severe
    • There is not nerve conduction distal to the site of injury (3 to 4 days after lesion)
    • EMG and NCV findings are as axonotmesis
    • Because of lack of nerve repair, surgical intervention is necessary


Notes

  • GCS cutoff is LESS THAN OR EQUAL TO 8
  • Peripheral nerve structure
    • Neurone
    • Myelin
    • Endoneurium
    • Perineurium
    • Epineurium
  • Panda Eye bruise
    • Limited by orbital fascia
      • c.f. Black eye
    • => Anterior skull fracture
  • Bruising around ear
    • => Posterior skull fracture
  • Aim for pCO2 of 3.5 kPa
    • => Cerebral vasoconstriction => Lowered ICP



Ċ
Kieran Gillick,
19 Oct 2012, 03:14
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