CMSD 642 Neuropathologies of Swallowing and Speech

California State University, Chico

Patrick McCaffrey, Ph.D

Chapter 2: Causes and Incidence: Traumatic Brain Injury (TBI)

1. According to Adamovich, Henderson, and Auerbach, (1984) as many as 400,000 head injuries occur in the United States each year. The severity of head injury has generally been classified as mild, moderate and severe. Mild head injury has been defined as concussion, while severe head injury means being in a coma for at least six hours. There does not appear to be a consensus for a definition of moderate head injury. Jennett and Teasdale developed the Glasgow Coma Scale in 1974 (Bach-y-Rita, 1989). It is a numerical scale that quantifies level of consciousness in response to three categories: response to pain, ability to open eyes, and ability to speak.
   
   

2. Types of Brain Injury (Urosevich, 1984)
   
   

   1. Coup-contrecoup: Coup can occur due to hitting one's head on a hard surface after a fall. There is a bruising of the brain and a laceration of blood vessels immediately below the injury site. Contre-coup injury occurs as the brain hits against the inside of the head just opposite the injury site. More serious hemorrhaging occurs when there are bony prominence where the brain comes in contact with the inside of the skull. Direct impact injury typically results in focal lesions just beneath the point of impact or on the opposite side of the brain.
      
   2. Acceleration-deceleration
      Motor vehicle accidents are the primary cause of this type of TBI. When there is a sudden stoppage of the vehicle the passenger's head is thrown forward violently, then thrown backward. The brain rebounds against the bony prominence of the skull, and may go through several oscillations. This often results in severe hemorrhaging. In addition, shearing injuries occur as the head twists dragging the brain along (rotational trauma). This can result in diffuse white matter/axonal injury.
   3. Typical Lesions Occurring with TBI (Pires, 1984): Many of the following lesions result in edema of brain tissue. It is extremely important that intra cranial pressure is managed. Your patients may be in a barbiturate induced coma, have their heads elevated, be hyperventilated, or heavily medicated (Bach-y-Rita, 1989).
      

1. Epidural Hematoma

Bleeding occurs above the dura mater, usually from meningeal arteries. The blood quickly accumulates, creating a space between the skull and the dura. The typical course for the patient is instantaneous loss of consciousness followed by a short period of lucidity, then a lapse into unconsciousness. The hematoma frequently exerts pressure on cranial nerves which can result in ipsalateral lower motor neuron paralysis. Because cranial nerves innervate muscles of swallowing and speech as well as those for eye movement, the paralysis can result in unilateral pupillary dilation and paralysis of the jaw, face, throat, larynx, or tongue.

2. Subdural Hematoma

Bleeding occurs into the potential space below the dura mater and above the arachnoid mater. It is typically venous and found above the frontal and temporal cerebral lobes. Since the primary and association motor cortices as well as pre-frontal cortex are in the frontal lobes damage there can result in swallowing, speech, language or cognitive problems. It is common for the appearance of symptoms to be delayed for several days or a week or more. A coma or less severe symptoms may develop. The latter include: seizures, unilateral or bilateral weakness or paralysis.

3. Intracerebral Hematoma

Bleeding is within the cerebrum and often includes sub-cortical structures. It most often occurs because of penetrating head wounds. The frontal and temporal lobes are frequently involved. Of course this type of injury could occur anywhere in the brain. Dysphagia, aphasia, apraxia, dysarthria, paralysis, as well as visual and other problems can occur.

4. Tentorial Herniation

Edema of the brain which occurs due to TBI, forces neural tissue through the tentorial notch between the cerebrum and cerebellum. This results in the squeezing of the brain stem (mid brain, pons, medulla). The cranial nerves are affected resulting in dysphagia, and speech problems, or even in death, as the medulla is important to respiration and circulation. Some of the initial symptoms of tentorial herniation are weakness, paralysis (often on one side), and visual disturbances (pupillary dilation, double vision). Respiration may be affected, the heart may be quite slow (bradycardia), or decortication (removal of cortical tissue) may be necessary.

5. Sites of lesion for traumatic brain injury

They are usually in the frontal or temporal lobe. If there is acceleration-deceleration injury with rotational trauma it can cause shearing of axons often resulting in dysarthria.

Copyright, 1998-2011. Patrick McCaffrey, Ph.D. This page is freely distributable.