Please consider accepting C, D and E as correct responses or excluding the
question from grading. I was not able to find anywhere in the notes or in chapter 4
œTheory and Practice of Psychiatry where the primary mechanism of injury for TBI
(closed head) was elucidated. I did not find any supporting evidence for was B “
hypoxia which was listed as a secondary mechanism of TBI in closed head injuries,
regarding answer A-microcirculatory compromise could be a primary injury; however,
ischemia is generally considered secondary as well.
According to the article œHead Trauma authored by Scott Shepard, MD available
at
http://www.emedicine.com/med/topic2820.htm (peer reviewed article retrieved on
21 Mar 05 via emedicine), œElevated ICP may result from the initial brain trauma or
from secondary injury to the brain. In adults, normal ICP is considered 0-15 mm Hg.
In young children, the upper limit of normal ICP is lower, and this limit may be
considered 10 mm Hg. Elevations in ICP are deleterious because they can result in
decreased CPP and decreased CBF, which, if severe enough, may result in cerebral
ischemia. Severe elevations of ICP are dangerous because, in addition to creating a
significant risk for ischemia, uncontrolled ICP may cause herniation. Herniation
involves the movement of the brain across fixed dural structures, resulting in
irreversible and often fatal cerebral injury. Another article œHead Injury by David A
Olson, MD available at
http://www.emedicine.com/neuro/topic153.htm (retrieved on
21 Mar 05) states, œOne study of CT images from 753 patients with severe head
injury from the National Institute of Health Traumatic Coma Data Bank in the United
States found evidence of intracranial hemorrhagic lesions in 27%. Traumatic
subarachnoid hemorrhage was even more frequent and occurred in 39% of patients.
Furthermore, diffuse cerebral edema also was present in 39%. Cerebral edema can
be unilateral or diffuse and can occur even in the absence of intracranial bleeding.
Severe brain edema probably occurs more commonly in children than in adults.
Finally, axonal injury increasingly has been recognized as a structural sequela of
brain injury. All of that was listed under structural changes with secondary insults
listed as hypotension and hypoxia. In short I™m not sure where the information came
from in our required material, but in my own search to find an explanation I have
encountered conflicting information.
Dr. Engel Response. Correct answer is C. I sat through this lecture and Dr. Lux clearly
and recurrently stated that the two primary mechanisms of closed head injury were
cerebral contusion and axonal strain. The only choice of these two that are mentioned here is axonal strain, making it the single best choice.
