head trauma part 1

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Emergency Radiology: Imaging of Head Trauma Rathachai Kaewlai, MD

Imaging of Head TraumaPart 1: Introduction

Rathachai Kaewlai, MDSpecialized in Body Imaging and Emergency Radiology

[email protected] 2006

The author is willing to receive any input, comments and corrections, Please do not hesitate to contact at the email address provided above.

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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

1. Brain is contained within the skull which is a rigid andinelastic container, so only small increases in volume canbe tolerated (Intracranial volume = Brain + CSF + Bloodvolume)

2. Cerebral perfusion pressure (CPP) in injured areas ispressure-passive flow (no autoregulation, cerebral bloodflow dependent on blood pressure)

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Introduction

• Traumatic brain injury: 2 categories1. 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 Imagingand 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 also known to be low yield (seenext page)

– With risk factors or neurologic deficit head CT withoutcontrast most appropriate and should be performed, brainMRI reserved for problem solving

– Children < 2 years old head CT withoutcontrast most appropriate and should be performed

According to American College of Radiology (ACR) Appropriateness Criteria

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• Indications for CT in patients with minor headinjury– Haydel MJ et al. Indications for CT in patients with minor

head injury. N 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 neurologicexamination underwent CT scans: 36 patients (6.9%) hadpositive scans

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

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• Indications for CT in patients with minor headinjury– 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 clinicalfindings was 100%.

• CT abnormalities in 93 patients with positive CT scans: cerebralcontusion (none had surgery), subdural hematoma (6% hadsurgery), subarachnoid hemorrhage (none had surgery),epidural hematoma (22% had surgery), depressed skullfracture (20% had surgery)

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• 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 caroid or vertebral artery dissection– MRI with MRA, or CT with CTA of the head and neck most

appropriate– Cerebral angiography reserved for problem solving


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• 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


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Skull Radiography

• 1/3 of patients with severe brain injury don’t havefracture

• Role of skull radiography in acute head injury– Calvarial fractures

• Linear fracture that is ‘in plane’ with axial CT scan can bemissed. 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 screenfor 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 hemorrhageregardless of location

– Widespread availability, rapid scanning, compatibility withother medical and life support devices

• Limitations– Insensitivity to detect small and nonhemorrhagic

lesions such as contusion, particularly when adjacent tobony surfaces, diffuse axonal injury

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

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

should undergo early noncontrast CT to look for…• Intracerebral hematoma• Midline shift• Increased intracranial pressure

– Patients with low-risk for intracranial injury: clinical selectionfor 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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• 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 inchildren less than 2 years

– CT order needs to be balanced with risk of radiationexposure

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Magnetic Resonance Imaging (MRI)

• Advantages– Sensitive for detection of diffuse axonal injury or

contusion with susceptibility sequence (T2 gradientecho), 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 windowdisplays on one brain CT exam.

Brain window Subdural window Bone window

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Make sure the first imageinclude the foramenmagnum (red circle),otherwise you will miss(impending) tonsillar herniation1 = cervicomedullary junction2 = CSF space (should be dark)3 = Cerebellar tonsils (tonsils arenot midline structures)

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5 = Pons (usually not clearly seen due to‘beam hardening artifact’ from bony skullbase)6 = Middle cerebellar peduncle(structure that connects pons andcerebellar hemispheres)7 = Cerebellar hemisphere8 = Forth ventricle (CSF cavity behindthe brainstem, slit-like appearance whennormal)

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7 = Cerebellum9 = Midbrain (heart-shaped structurenormally surrounded by CSF. Effacement ofCSF may suggest early brain herniation)10 = Temporal lobe11 = Temporal horn of lateralventricle (Look for earliest hydrocephalushere. Normally slit-like, or curvilinear)12 = Uncus (Most medial portion oftemporal lobes; uncal herniation is calledwhen uncus displaces medially and obliteratesthe CSF space on the side of midbrain)13 = CSF cistern (Not seeing CSF aroundmidbrain may be abnormal; that’s whatradiologists call ‘effacement of the cistern’ as asign of cerebral herniation. Also a place tolook for subarachnoid hemorrhage)

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14 = Anterior falx (Know where it is, soyou can draw a ‘midline’ to see if there is‘midline shift’ or not)15 = Posterior falx16 = Basal ganglia (Lateral to thefrontal horn of lateral ventricle)17 = Thalamus (lateral to the thirdventricle which is very narrow here)18 = Sylvian fissure (CSF spacedividing frontal from temporal lobes. Look forsubarachnoid hemorrhage here)Red line = Cerebral convexity (Lookfor extra-axial hemorrhage here, better seenin ‘subdural window’)

• Intra-axial = any pathology ‘in’ the brainparenchyma• Extra-axial = any pathology ‘not in theparenchyma’ e.g. subarachnoid, subduraland epidural pathology

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19 = Lateral ventricle20 = Septum pellucidum (midlinestructure dividing right and left lateralventricles; helps in measuring degree ofmidline shift)

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2 = CSF space (Look for subarachnoidhemorrhage here)

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

22 = Mastoid air cells (should befilled with air density, otherwise fracture ofthe skull base should be suspected)

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23 = Sphenoid sinus (Look for fluid orblood density, air-fluid level which mayrepresent skull base fracture)

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Checklist for Trauma Brain 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) 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 temporomandibular 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…– Does not represent the official statements or views of the

Thai Association of Emergency Medicine.– 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.

head trauma part 1

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