Introduction to
Traumatic Brain Injury
Brian L. Edlow, MS4
University of Pennsylvania
School of Medicine
December 4, 2006
Goals
1. Understand that traumatic brain injury is a
process, not an event
2. Understand the 4 main pathophysiologic
mechanisms involved in traumatic brain
injury
3. Understand basic strategies for treatment
Severe Traumatic Brain Injury (TBI)

Definition: Head trauma associated with a
Glasgow Coma Score of ≤ 8
Best Eye
Response
1.
2.
3.
4.
No eye opening
Eye opening to
pain
Eye opening to
verbal
command
Eye opening
spontaneously
Best Verbal
Response
1.
2.
3.
4.
5.
No verbal
response
Incomprehensible
sounds
Inappropriate
words
Confused words
Appropriate
verbal responses
Best Motor
Response
1.
2.
3.
4.
5.
6.
No motor
response
Extension to pain
Flexion to pain
Withdrawal from
pain
Localizing to pain
Obeys
commands
Severe TBI - Demographics

1.5 million cases per year in U.S. (Population
300 million)
 Causes: Motor vehicle
accident (~45%), falls
(~30%), occupational
accidents (~10%),
recreational
accidents
(~10%), assaults
(~5%)

Highest risk: children,
adolescent/young adult
men, elderly
Severe TBI - Pathophysiology

TBI is a process, not an event!


Secondary injury can be more damaging than
primary injury
4 Main Mechanisms of Brain Injury
1.
Brain Contusion
2.
Increased intracranial pressure ( ICP)
3.
Diffuse Axonal Injury
4.
Stroke (ischemic and/or hemorrhagic)
Mechanism 1: Brain Contusion

A brain contusion is defined by
cell death accompanied by
hemorrhage (leakage of blood)

The soft brain tissue is
vulnerable to contusion in head
trauma

The contusion often occurs at a
site distant from the point of
impact
Gross brain image from
http://neuropathology.neoucom.edu/chapter4/chapter4bContusions_dai_sbs.html#contusion
Mechanism 2: ICP
- Understanding the Determinants of
Intracranial Pressure 
The volume of the intracranial vault =

Intracranial Contents:




80% brain tissue
10% blood
10% cerebrospinal fluid
An increase in the volume of any of these intracranial
contents causes increased intracranial pressure
1.
The brain can swell (edema)
2.
Excess blood can accumulate due to hemorrhage
3.
Cerebrospinal fluid can accumulate due to blockage of
outflow
Mechanism 2: ICP

Key Concept #1: The intracranial vault
is a fixed volume --> Bone does not
expand!
Skull image from www.mnsu.edu
Mechanism 2: ICP
- Understanding the Physics of Intracranial
Pressure -
Pressure
ICP > 20 mmHg
(mmHg)
Volume (mL)
Intracranial Pressure Rises as Brain+Bood+CSF volume Increases
Mechanism 2: ICP
- Understanding the Physics of Intracranial
Pressure ICP
CPP
This patient has dangerously high intracranial pressures, which
increase the likelihood of morbidity and mortality
Mechanism 2: ICP

Key Concept #2: There is only one way out of the
intracranial vault --> the opening at the base of
the skull known as the foramen magnum
Skull base image from www.octc.kctcs.edu
3D CT Angiogram from
www.auntminnie.com/.../
65000/66000/66173.asp
Mechanism 2: ICP

Key Concept #3:
When the brain is
squeezed through the
foramen magnum
(herniation), the
brainstem is
compressed, the
patient stops
breathing, and the
patient dies
Herniation schematic from Robbins and Cotran. Pathologic Basis of Disease. 7th ed. Philadelphia: Elselvier; 2005.
Causes of ICP: Epidural Hematomas
Figure 7-15 Examples (A, B-arrows) of epidural hematomas in CT scans on the patient's right
side. The smaller lesion in A is obviously of traumatic origin; this patient has soft tissue damage, a
fractured skull, blood in the substance of the brain, and blood in the anterior horn of the lateral
ventricle and in the third ventricle. The cause of the larger lesion (B) is not obvious.
Causes of ICP: Sudural Hematomas
Figure 7-16 An example of a subdural hematoma (arrows) in CT scan on the patient's left side.
This lesion is long and thin and extends for considerable distance over the surface of the
hemisphere: note the shift in the midline.
Causes of ICP: Swelling
Observe swelling (darker tissue) on brain CT scan of a 7-month-old
victim of child abuse. What other injuries are present?
Head CT from rad.usuhs.mil/rad/ home/peds/ihsdarrow.jpg
Causes of ICP: Swelling
Observe diffuse swelling (yellow tissue) and expansion of
brain tissue into ventricles
Gross brain specimen from neuropathology.neoucom.edu
Causes of ICP: Swelling
Observe widening and flattening of gyri on brain surface
Mechanism 3: Diffuse Axonal Injury
 Occurs
in up to 1/2 of traumatic brain
injuries1

Is a diffuse form of injury, meaning that
damage occurs over a more widespread
area than in focal brain injury
 Involves
the shearing of axons in the white
matter tracts
1: http://en.wikipedia.org/wiki/Diffuse_axonal_injury
Mechanism 3: Diffuse Axonal Injury

Is one of the major causes of
unconsciousness and persistent vegetative
state after head trauma.

Over 90% of patients with severe DAI never
regaining consciousness (those that do wake
up often remain significantly impaired)
Mechanism 3: Diffuse Axonal Injury
A microscopic view of axonal degeneration
Mechanism 4: Stroke

Ischemic Stroke



Caused by decreased oxygen delivery to brain
tissue
Can occur in trauma secondary to swelling, which
compresses nearby arteries
Hemorrhagic Stroke


Decreased oxygen delivery because blood is
leaking into brain tissue and not entering the
capillary network
Can occur as a primary or secondary injury

Severe TBI - Basic Principles of
Clinical Management
Monitor intracranial pressure (invasively) and
intervene to lower ICP when necessary






Seizure prophylaxis


Elevate head of bed
Medications to decrease swelling
Decrease brain activity to reduce blood delivery and swelling
--> “medically induced coma”
Hypothermia
Surgical Decompression when risk for herniation is high
Seizures occur in up to 20% of severe TBI patients, with
~50% occurring within first 24 hours1
Other priorities

Adequate nutrition, correction of electrolyte abnormalities,
strict control of blood sugar, strict temperature regulation
1: “Post-traumatic Seizures and Epilepsy.” www.uptodate.com. May 29, 2006.
Severe TBI - Prognosis
 The
Impact of ICP: Patients with mean ICP greater
than 20 mmHg during hospitalization have 47%
mortality vs. patients with mean ICP below 20
mmHg, who have 17% mortality (p < 0.001)1
 17%
will have seizures during the 2-year posttrauma period2
 The
length of time a patient spends in a coma
correlates to both post-traumatic amnesia and
recovery times
1: Balestreri M, Czosnyka M et al. Impact of intracranial pressure and cerebral perfusion pressure on severe disability and mortality
after head injury. Neurocrit Care. 2006,;4(1):8-13.
2: Englander J; Bushnik T et al. Analyzing risk factors for late posttraumatic seizures: a prospective, multicenter investigation. Arch
Phys Med Rehabil 2003 Mar;84(3):365-73.
Severe TBI - Prognosis
- The Stories of DM and PV 
Case 1 - DM





18-year-old boy hit by car while riding bike
Severe TBI with frequent spikes in ICP, ventilator dependant
2 weeks in coma
Walked out of hospital after 2.5 weeks, able to communicate
with family
Case 2 - PV




38-year-old man falls down stairs in bar
Severe TBI --> goes in and out of coma for 2 weeks
2 weeks into hospital course, swelling increases so much
that temporal lobe herniates into brain stem, causing
permanent loss of consciousness
Dies after 1.5 months in hospital of brain infection,
respiratory failure
Looking to the future…
Will new imaging technologies lead to advances in patient care?