The Canadian Assessment of Tomography for Childhood Head injury rule (CATCH rule) assists in assessing the level of risk associated with a child's head injury to determine the potential need for a CT scan. It evaluates specific factors that could suggest a significant brain injury, categorizing the risk into low, medium, or high.

You need to answer seven questions with either "Yes" or "No":

- GCS < 15 at 2 hours after injury
- Suspected open or depressed skull fracture
- History of worsening headache
- Irritability on examination
- Any sign of basal skull fracture
- Large boggy scalp hematoma
- Dangerous mechanism of injury

Here’s how the risk is interpreted based on these responses:

- High risk: If any of these conditions are true, it indicates a high possibility of significant head injury, necessitating immediate imaging and medical evaluation:
  - GCS < 15 at 2 hours after injury
  - Suspected open or depressed skull fracture
  - History of worsening headache
  - Irritability on examination

- Medium risk: This suggests a moderate probability of brain injury, which may need further observation or imaging, if any of the following are true:
  - Any sign of basal skull fracture
  - Large boggy scalp hematoma
  - Dangerous mechanism of injury

- Low risk: If all the assessment questions yield a "No," it indicates a low likelihood of significant brain injury, suggesting that a CT scan may not be necessary.

By answering these questions, the rule helps identify children who might require just observation and those who would benefit from further diagnostic imaging to prevent unnecessary scans and interventions.

The Canadian Assessment of Tomography for Childhood Head injury rule, or CATCH rule, is a clinical calculator used in the pediatric population, specifically for children with minor head injuries. This scoring system is designed to help clinicians determine which children require a computed tomography (CT) scan to rule out clinically important traumatic brain injury (ciTBI). The CATCH rule includes factors such as age, mechanism of injury, and clinical symptoms to stratify the risk of ciTBI. The clinical utility of this calculator is to reduce unnecessary radiation exposure from CT scans in children with minor head injuries, while still identifying those at risk for significant injury. The CATCH rule should not be used in children with severe injury, those with a Glasgow Coma Scale score of less than 13, or those with known brain pathology.