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Imaging of Head Trauma Part 1: Introduction

Rathachai Kaewlai, MD

www.RadiologyInThai.com

Created: December 2006

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Outline

  When to do brain imaging in trauma setting?

  What imaging is appropriate?

  Advantage and disadvantage of each imaging modality

  Review of important cranial CT anatomy

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Introduction

  Significance of craniocerebral injuries   Common cause of hospital admission following trauma   High morbidity and mortality particularly in adolescent and

young adults

  Concepts   Brain is contained within the skull which is a rigid and inelastic

container, so only small increases in volume can be tolerated (Intracranial volume = Brain + CSF + Blood volume)

  Cerebral perfusion pressure (CPP) in injured areas is pressure-passive flow (no autoregulation, cerebral blood flow dependent on blood pressure)

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Introduction

  Traumatic brain injury: 2 categories 1.  Primary injury

–  Initial injury to the brain as a result of direct trauma

–  Example: hematoma, diffuse axonal injury, contusion

2.  Secondary injury –  Subsequent injury to the brain after the initial insult

–  Result from systemic hypotension, hypoxia, elevated intracranial pressure (ICP) or biochemical insults

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When to Do Imaging and What to Do?

  Minor or mild acute closed head injury (GCS > 13)   Without risk factors or neurologic deficit head CT without

contrast can be performed but known to be low yield (see next page)

  With risk factors or neurologic deficit head CT without contrast most appropriate and should be performed, brain MRI reserved for problem solving

  Children < 2 years old head CT without contrast most appropriate and should be performed

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According to American College of Radiology (ACR) Appropriateness Criteria

When to Do Imaging and What to Do?

  Indications for CT in patients with minor head injury   Haydel MJ et al. Indications for CT in patients with minor

head injury. New Engl J Med 2000;343:100-5.   520 patients with minor head injury who had a normal Glasgow

Coma Scale and normal findings on a brief neurologic examination underwent CT scans: 36 patients (6.9%) had positive scans

  All patients with positive scans had one of the clinical findings: short-term memory deficit, drug or alcohol intoxication, physical evidence of trauma above clavicles, age > 60 yr, seizure, headache, vomiting, or coagulopathy

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When to Do Imaging and What to Do?

  Indications for CT in patients with minor head injury   Haydel MJ et al. Indications for CT in patients with minor

head injury. N Engl J Med 2000;343:100-5.   Results were tested in another 909 patients; using at least one of

the clinical findings above, the sensitivity of seven clinical findings was 100%.

  CT abnormalities in 93 patients with positive CT scans: cerebral contusion (none had surgery), subdural hematoma (6% had surgery), subarachnoid hemorrhage (none had surgery), epidural hematoma (22% had surgery), depressed skull fracture (20% had surgery)

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When to Do Imaging and What to Do?

  Moderate or severe acute closed head injury   Head CT without contrast most appropriate and should be

performed   X-ray and/or CT of cervical spine also appropriate and

recommended   MRI reserved for problem solving

  Rule out carotid or vertebral artery dissection   MRI with MRA, or CT with CTA of the head and neck most

appropriate   Cerebral angiography reserved for problem solving

8 According to American College of Radiology (ACR) Appropriateness Criteria

When to Do Imaging and What to Do?

  Penetrating injury, stable, neurologically intact   Head CT without contrast most appropriate and should be performed

  Skull x-ray also appropriate if calvarium is the site of injury

  C spine x-ray or CT appropriate if neck or C-spine is the site of injury

  CTA of head and neck if vascular injury suspected

  Skull fracture

  Head CT without contrast most appropriate and should be performed

  CTA of head and neck if vascular injury suspected

9 According to American College of Radiology (ACR) Appropriateness Criteria

Skull Radiography

  1/3 of patients with severe brain injury don’t have fracture

  Role of skull radiography in acute head injury   Calvarial fractures

  Linear fracture that is ‘in plane’ with axial CT scan can be missed. Scout image of head CT, or CT reformation is useful

  Penetrating injuries   Provide rapid assessment of degree of foreign body penetration, e.g. stab

wounds

  Radiopaque foreign bodies   Example: patients with gunshot wounds to the head (to screen for retained

intracranial bullet fragments)

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Computed Tomography (CT)

  Advantages   High sensitivity for demonstrating mass effect, ventricular size and

configuration, bone injury, acute hemorrhage regardless of location

  Widespread availability, rapid scanning, compatibility with other medical and life support devices

  Limitations   Insensitivity to detect small and nonhemorrhagic lesions such as

contusion, particularly when adjacent to bony surfaces, diffuse axonal injury

  Relatively insensitive to detect early brain edema, hypoxic-ischemic encephalopathy (HIE)

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Computed Tomography (CT)

  Role of CT in acute head injury   Patients with moderate-risk or high-risk for intracranial injury should

undergo early non-contrast CT to look for…   Intracerebral hematoma

  Midline shift

  Increased intracranial pressure

  Patients with low-risk for intracranial injury: clinical selection for CT is still problematic   CT may be able to triage this patient group to admission, surgery or discharge

  CT may lower the cost of hospital admission for observation

  Trade-off with greater use of CT in emergency setting

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Computed Tomography (CT)

  Repeat head CT   Required for clinical or neurologic deterioration, especially within

72 hours after trauma   Detection of delayed hematoma, hypoxic-ischemic lesions and

cerebral edema

  Pediatric patients   Lower threshold for doing a CT scan

  Clinical criteria for scanning is less reliable, particularly in children less than 2 years

  CT order needs to be balanced with risk of radiation exposure

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Magnetic Resonance Imaging (MRI)

  Advantages   Sensitive for detection of diffuse axonal injury or contusion with

susceptibility sequence (T2 gradient echo), distinguish different ages of blood

  Useful for screening of vascular lesions such as thromboses, pseudoaneurysms, or dissection

  Limitations   Insensitive for subarachnoid hemorrhage, air and fracture   Certain absolute contraindications, e.g. pacemaker   Limited availability in acute setting, longer imaging time (than CT),

incompatibility with some medical devices

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Magnetic Resonance Imaging (MRI)

  Role of MRI in acute head injury   Problem solving tool when CT is inconclusive or high clinical

suspicion   Diffuse axonal injury: CT is less sensitive than MRI. For example,

patients with severe head injury but normal CT

  Brain contusion

  Vascular examinations of the brain and neck   Suspicion of dissection, aneurysm or thrombosis

  CT angiography also has a competitive role as MR angiography

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Brain CT: Normal Anatomy

  Make sure to look at all 3 different window displays on one head CT exam.

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Brain window Subdural window Bone window

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1 2

1 3 3 Make sure the first image include the foramen magnum (red circle), otherwise you will miss (impending) tonsillar herniation 1 = cervicomedullary junction 2 = CSF space (should be dark) 3 = Cerebellar tonsils (tonsils are not midline structures)

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5 6

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5 = Pons (usually not clearly seen due to ‘beam hardening artifact’ from bony skull base) 6 = Middle cerebellar peduncle (structure that connects pons and cerebellar hemispheres) 7 = Cerebellar hemisphere 8 = Forth ventricle (CSF cavity behind the brainstem, slit-like appearance when normal)

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7 = Cerebellum 9 = Midbrain (heart-shaped structure normally surrounded by CSF. Effacement of CSF may suggest early brain herniation)

10 = Temporal lobe 11 = Temporal horn of lateral ventricle (Look for earliest hydrocephalus here. Normally slit-like, or curvilinear) 12 = Uncus (Most medial portion of temporal lobes; uncal herniation is called when uncus displaces medially and obliterates the CSF space on the side of midbrain) 13 = CSF cistern (Not seeing CSF around midbrain may be abnormal; that’s what radiologists call ‘effacement of the cistern’ as a sign of cerebral herniation. Also a place to look for subarachnoid hemorrhage)

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14 = Anterior falx (Know where it is, so you can draw a ‘midline’ to see if there is ‘midline shift’ or not) 15 = Posterior falx 16 = Basal ganglia (Lateral to the frontal horn of lateral ventricle) 17 = Thalamus (lateral to the third ventricle which is very narrow here) 18 = Sylvian fissure (CSF space dividing frontal from temporal lobes. Look for

subarachnoid hemorrhage here) Red line = Cerebral convexity (Look for extra-axial hemorrhage here, better seen in ‘subdural window’)

•  Intra-axial = any pathology ‘in’ the brain parenchyma •  Extra-axial = any pathology ‘not in the parenchyma’ e.g. subarachnoid, subdural and epidural pathology

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19 = Lateral ventricle 20 = Septum pellucidum (midline structure dividing right and left lateral ventricles; helps in measuring degree of midline shift)

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2 = CSF space (Look for subarachnoid hemorrhage here)

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Red lines = Temporomandibular joint (socket) 21 = Condyle of mandible (ball; should sit in the socket. Missing fracture or dislocation in this region will cause patients’ long term disability)

22 = Mastoid air cells (should be filled with air density, otherwise fracture of the skull base should be suspected)

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23 = Sphenoid sinus (Look for fluid or blood density, air-fluid level which may represent skull base fracture)

Checklist for Trauma Head CT

  Have 3 different windows to look for different pathology (brain, subdural and bone windows)

  First image includes foramen magnum

  Look first for the pathology that needs emergent Rx

  Hydrocephalus

  Look for primary pathology (hemorrhage in different compartments, depressed skull fracture)

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Checklist for Trauma Head CT

  Look for secondary pathology (brain herniation, midline shift)

  Look at the mastoid and sphenoid sinuses for hemorrhage which implies skull base fractures

  Always look at scout CT image for fracture ‘in plane’ with axial scans

  Look at temporo-mandibular joints for fracture and/or dislocation

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Traumatic brain pathology will be continued on ‘Part 2’

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  The information provided in this presentation…   Is intended to be used as educational purposes only.

  Is designed to assist emergency practitioners in providing appropriate radiologic care for patients.

  Is flexible and not intended, nor should they be used to establish a legal standard of care.

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