Is assault considered a dangerous mechanism on a Canadian head computed tomography (CT) scan?

Assault as a Dangerous Mechanism in Canadian Head CT Decision Rules

Assault is not specifically listed as a dangerous mechanism of injury in the Canadian CT Head Rule, but certain types of assault with high-impact mechanisms may qualify as dangerous mechanisms requiring CT imaging.

Understanding the Canadian CT Head Rule

The Canadian CT Head Rule (CCHR) is a validated clinical decision tool that helps determine which patients with minor head injury require head CT scanning. According to the guidelines, a "dangerous mechanism" is defined as 1:

• Pedestrian struck by vehicle
• Occupant ejected from motor vehicle
• Fall from height greater than 3 feet or 5 stairs

The CCHR consists of five high-risk factors that are 100% sensitive for predicting need for neurosurgical intervention 2:

1. Failure to reach GCS of 15 within 2 hours
2. Suspected open skull fracture
3. Any sign of basal skull fracture
4. Vomiting >2 episodes
5. Age >65 years

And two medium-risk factors for predicting clinically important brain injury:

1. Amnesia before impact >30 minutes
2. Dangerous mechanism of injury

Assault and Head CT Decision-Making

While assault itself is not explicitly listed as a dangerous mechanism in the CCHR, the clinical context of the assault matters significantly:

• High-impact assaults: Assaults involving significant force (such as being struck with a weapon, punched repeatedly, or having the head slammed against a hard surface) may be considered under dangerous mechanisms based on clinical judgment 1.

• Risk stratification: The American College of Emergency Physicians (ACEP) guidelines recommend considering CT for patients with head trauma and no loss of consciousness if there is "a dangerous mechanism of injury" among other factors 1.

• Clinical application: In practice, physicians must evaluate the specific circumstances of the assault, including the force involved, potential for rotational acceleration-deceleration injuries, and presence of other risk factors.

Important Considerations

1. Mechanism evaluation: The key is to assess the force and nature of the assault, not just the fact that an assault occurred.

2. Additional risk factors: Even if the assault itself isn't considered a dangerous mechanism, CT would still be indicated if other CCHR criteria are met (e.g., vomiting, age >65, signs of basilar skull fracture).

3. Clinical judgment: Studies show that physicians often order CTs in borderline cases due to concerns about missing injuries, with "physician reassurance" (24.6%) and "patient reassurance" (24.2%) being common reasons 3.

4. Sensitivity vs. specificity: The CCHR has demonstrated 100% sensitivity for detecting injuries requiring neurosurgical intervention, with higher specificity (37.2%-39.7%) compared to other decision rules like the New Orleans Criteria 4.

Bottom Line

While assault per se is not explicitly listed as a dangerous mechanism in the Canadian CT Head Rule, high-impact assaults with significant force may qualify based on clinical judgment. The decision to perform CT should be based on the specific mechanism of injury and presence of other risk factors rather than simply the occurrence of an assault.