Introduction to Traumatic Brain Injury

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. Best Verbal Response 1. 2. 3. 4. 5. Best Motor Response 1. 2. 3. 4. No eye opening Eye opening to pain Eye opening to verbal command Eye opening spontaneously No verbal response Incomprehensible sounds Inappropriate words Confused words Appropriate verbal responses 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. 3. Increased intracranial pressure ( ICP) 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. 2. 3. The brain can swell (edema) Excess blood can accumulate due to hemorrhage 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 (mmHg) ICP > 20 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  Monitor intracranial pressure (invasively) and intervene to lower ICP when necessary    Severe TBI - Basic Principles of Clinical Management 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  Seizure prophylaxis  Seizures occur in up to 20% of severe TBI patients, with ~50% occurring within first 24 hours 1  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 of time a patient spends in a coma correlates to both post-traumatic amnesia and recovery times  The length 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?