Blunt Head Trauma and Head CT

Like many Trauma Centers, many of our patients come with blunt head trauma (BHT). BHT is often presents with other injuries, but is not uncommonly the sole presenting complaint.

Since the mid-1970s, non-contrast head CT (hCT) has become the gold standard modality to evaluate BHT. And over the past 40 years the indications for hCT has evolved. Many studies have attempted to provide data to maximize its utility. One of the more cited studies is The Canadian CT Head Rule study (Lancet 2001; 357: 1391-96) - a prospective cohort study that ultimately provided a set of 7 “rules” for identifying high and middle risk patients in whom hCT might prove useful.

Tests are most useful when they serve to help answer a specific question. The Canadian CT Head Rule took this principle and aimed to add some evidence to the two main questions we hope to answer when ordering hCTs on patients with BHT. The first question we want to answer is, “Does this patient have a head injury that requires neurosurgical intervention? The second question is, “Does this patient have an injury that will result in long-term disability, but doesn’t necessarily need intervention?” Based on the authors’’ analysis, the Canadian CT Head Rule came up 7 rules: 5 rules for identifying patients at risk for needing neurosurgical intervention and 2 rules that identified patients at risk for finding brain injury on CT but not necessarily requiring intervention. The rules are:

Risk for requiring neurosurgical intervention (“High Risk”) – Meet any one of the following places patient in this category

1.      GCS < 15 at 2h after injury

2.      Suspected skull fracture

3.      Sign of basal skull fracture

4.      Vomiting 2 or more times after event

5.      ≥ 65 yo

Risk for finding brain injury on CT (“Medium Risk”) - Meet any one of the following places patient in this category

1. Amnesia before event >30 min
2. Dangerous mechanism (high speed MVC, auto-ped, fall from height >3ft or five stairs

Using these rules, the original Lancet study revealed data that by using the five “High Risk” rules resulted in zero missed patients (100% sensitivity) and was nearly 100% for the “Medium Risk” patient (98.4% sensitivity). Specificity for high and medium risk categories was 68.7% and 49.6% respectively.  The data for sensitivities supports hCT as an excellent screening test. The relatively low specificities are a part of what keep the question about how best to use hCT in BHT somewhat controversial. The data from the Canadian CT Head Rule also serves to emphasize the importance of community-specific prevalence data to best determine BHT and hCT ordering protocols for individual trauma centers.

At CCH, our practice is to get hCTs for patients with loss of consciousness (LOC) or any amnesia to the event. Concern for skull fracture, by history or exam, is also criteria we use but most of these patients meet our first criteria. From time to time, age and mechanism serve as the deciding factors that lead to hCT, even in the absence LOC or amnesia, but these decisions are made on a case by case basis. Even of the hCTs that have grossly positive findings, only a small minority of those lead to neurosurgical intervention. But in addition to ruling out a grossly positive lesion, there is some additional long-term utility in these negative tests.

A negative hCT (or a series of negative hCTs) can often help monitor and guide outpatient care for some patients with BHT.  In the absence of gross CT findings, many patients will still have serious and persistent long-term neurocognitive problems referred to as mild traumatic brain injury (MTBI). The pathophysiology of MTBI is currently attributed to diffuse axonal injury (DAI) from shear forces. Support for this theory comes from autopsy data since hCT does not detect DAI, which explains how some patients with negative hCTs can still have serious issues. The EAST Guidelines for the Management of Mild Traumatic Brain Injury (J Trauma. 51(5):1016-1026, November 2001) are a good resource for further information on MTBI.

Ultimately, there are many unanswered questions regarding the best way to initially evaluate patients with BHT. Currently, hCT serves as our best tool to quickly screen for potentially catastrophic injuries and to help monitor patients with or without gross brain injury. LOC and amnesia are the clinical characteristics we use to identify patients who require hCT, but absence of these does not necessarily exclude our use of hCT.

Thanks to Allan Peetz, MD for this submission.