Hounsfield Unit Changes Over Time in Contusions of the Brain
Kevin Moore II; Addison Willett; Eduardo Gonzalez-Toledo, MD, PhD; Asser Youssef, MD, FACS, FICS
In the United States, traumatic brain injuries are an important cause of death and disability, often with sig- nificant financial and legal consequences. Although it is generally accepted by neuroradiologists that the density of cerebral contusions decreases over time, previous research has not addressed this phenomenon directly. In the current study, we reviewed charts of patients who had suffered cerebral contusions and had at least two subsequent computed tomography scans in order to determine whether Hounsfield Units, a measure of density, decreased over time. We found that 100% of contusions decreased in Hounsfield Units over time. In addition, we found that the rate of decrease in density appears to be higher in the first 100 days after the injury. These findings are especially applicable in the area of forensics. For example, they could be used to determine the relative age of two separate brain contusions in the same patient.
INTRODUCTION Trauma is well known to be a major cause of loss of life and disability in the United States. According to the National Trauma Institute, trauma accounts for 47% of all deaths in people under age 44, making it the number one killer in this age group. 1 Traumatic brain injuries (TBI) are a major contributor to death and disability in trauma victims, with the Centers for Disease Control (CDC) estimating that approximately 1.7 million TBIs occur every year. 2 Cerebral contusion is a common type of TBI that can result from a variety of traumatic etiologies and can result in a wide range of disabilities, depending on location and severity. Computed tomography (CT) scans are commonly used to assist in evaluating trauma patients once the primary survey has been completed. In CT scans, the Hounsfield Unit (HU) is used as a measure of the relative density of a certain area of tissue. It is generally well accepted among neuroradiologists that the HU (and therefore density) of cerebral contusions decreases over time. However, it has not been well characterized in previous research whether HUs change predictably over time in cerebral contusions. This study aims to determine whether the HUs decrease as the wound ages. MATERIALS AND METHODS In this IRB-approved retrospective chart review, we analyzed 1,674 records of patients admitted to the ICU with traumatic head injuries that had at least one CT scan of the brain. Patients with cerebral contusions and at least
one follow-up CT scan of the brain were included. The to- tal number of patients included was 31, and there were 83 total CT scans obtained from these patients. The number of scans per patient ranged from two to nine. Using the Osiris program, we sampled the contusion using the slice with the greatest apparent area of injury. We then calculated the average HU value of the contusion, repeated the process for any subsequent scans, and compared the values to see whether the average HU decreased over time. We also used statistical software to determine whether there was a significant correlation between the time elapsed and the HU. Furthermore, we investigated whether the correlation differed when considering different time periods relative to the initial scan. RESULTS The average HU value decreased over time in 100% of the contusions (n=31). There was also a correlation be- tween HU and time elapsed when all scans were analyzed together (R=-.533, N=83, P<.001) When the average HU was correlated with time elapsed for scans <100 days after the initial scan, the strength of the negative correlation increased. (R=-.603, N=51, P<.001). The correlation also increased when the first scan (time elapsed = 0 days) was omitted (R=-0.712, N=36, P<.001). At time periods greater than 150 days, there was no significant correlation (R -.201, N=14, P=.491). The average HU of the initial scans ranged from 11.8 to 54.3, with o =10.81.
J La State Med Soc VOL 166 May/June 2014 119
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