Canadian CT Head Rule: the seven findings and how they combine
The Canadian CT Head Rule combines seven findings after a minor head injury: five high-risk findings (Glasgow Coma Scale below 15 two hours after the injury, a suspected open or depressed skull fracture, any sign of a basal skull fracture, two or more episodes of vomiting, and age 65 or older) and two medium-risk findings (amnesia for more than 30 minutes before the impact, and a dangerous mechanism). Magent's calculator reports whether any high-risk finding is present, whether any medium-risk finding is present, and a combined true/false result that's true when either is.
This page doesn't give disposition advice. It shows how the findings combine. What to do with the result depends on the clinical context.
Not a medical device. Not a diagnosis or dosing recommendation.
What is the Canadian CT Head Rule?
The Canadian CT Head Rule (CCHR, also searched as the Canadian head CT rule or the Stiell CT head rule) is a clinical decision rule from Ian G. Stiell and colleagues, published in The Lancet in 2001. The title describes it as a rule "for patients with minor head injury."
The 2001 abstract says the authors "derived a CT head rule which consists of five high-risk factors ... and two additional medium-risk factors." It's a set of yes/no findings, not a points score.
The Canadian CT Head Rule logic
high_risk = gcs_lt_15_at_2h
OR suspected_open_or_depressed_skull_fx
OR any_sign_basal_skull_fx
OR vomiting_two_or_more
OR age >= 65
medium_risk = amnesia_before_impact_gt_30min
OR dangerous_mechanism
result = high_risk OR medium_riskExact expression the calculator uses:
ct indicated if any high-risk (gcs_lt_15_at_2h or suspected_open_or_depressed_skull_fx or any_sign_basal_skull_fx or vomiting_two_or_more or age >= 65) or any medium-risk (amnesia_before_impact_gt_30min or dangerous_mechanism)The two groups are checked independently. A person can have a high-risk finding, a medium-risk finding, both or neither.
High-risk findings
| Input | Meaning |
|---|---|
gcs_lt_15_at_2h | Glasgow Coma Scale score still below 15 two hours after the injury. The caller answers true or false; the calculator doesn't take a GCS number. |
suspected_open_or_depressed_skull_fx | A suspected open or depressed skull fracture |
any_sign_basal_skull_fx | Any sign of a basal skull fracture: blood behind the eardrum (hemotympanum), "raccoon eyes," cerebrospinal fluid leaking from the ear or nose, or Battle's sign |
vomiting_two_or_more | Two or more episodes of vomiting |
age | Age in years, 16 to 120. Age 65 or older is a high-risk finding; 64 isn't. |
Medium-risk findings
| Input | Meaning |
|---|---|
amnesia_before_impact_gt_30min | Memory loss for more than 30 minutes before the impact |
dangerous_mechanism | A dangerous mechanism, as assigned by the caller. Magent's record lists these examples: a pedestrian struck by a motor vehicle, an occupant ejected from a motor vehicle, or a fall from more than 3 feet or 5 stairs. |
How to apply the rule
- Check the five high-risk findings. If any one is present, the high-risk group is positive.
- Check the two medium-risk findings. If either is present, the medium-risk group is positive.
- Combine. The overall result is true if either group is positive, and false if neither is.
What the calculator returns
Magent's calculator returns the combined true/false result (in a field named ct_indicated), separate true/false answers for the high-risk and medium-risk groups, the age it used, and a line for each of the seven findings.
Worked examples
These use Magent's own expected values for the calculator. Unlisted findings are "no".
Example 1: age 40, nothing present
- High-risk group: age 40 isn't 65 or older; no other high-risk finding → negative.
- Medium-risk group: negative.
- Combined result: false.
Example 2: age 65
- High-risk group: age 65 → positive.
- Medium-risk group: negative.
- Combined result: true.
Example 3: age 64
- Age 64 isn't 65 or older; nothing else present.
- Combined result: false.
Example 4: two or more episodes of vomiting
- High-risk group: positive.
- Combined result: true.
Example 5: dangerous mechanism alone
- High-risk group: negative.
- Medium-risk group: dangerous mechanism → positive.
- Combined result: true.
Example 6: age 16
- Age 16 is the youngest age the calculator accepts. It isn't a high-risk finding.
- Combined result: false.
Canadian CT Head Rule reference values
These are Magent's expected values for the calculator. Age 40 with no findings gives a combined result of false, and so do age 64 and age 16 with no findings. Age 65 alone puts the person in the high-risk group, so the combined result is true. At age 40, each high-risk finding on its own (GCS below 15 at 2 hours, a suspected open or depressed skull fracture, a sign of basal skull fracture, or vomiting 2 or more times) gives true through the high-risk group. Each medium-risk finding on its own (amnesia before impact over 30 minutes, or a dangerous mechanism) gives true through the medium-risk group.
History of the Canadian CT Head Rule
The rule comes from Ian G. Stiell, George A. Wells, Katherine Vandemheen and colleagues, The Canadian CT Head Rule for patients with minor head injury, The Lancet, 2001 (volume 357, issue 9266, pages 1391–1396).
The abstract notes "much controversy about the use of computed tomography (CT) for patients with minor head injury." The authors "carried out this prospective cohort study in the emergency departments of ten large Canadian hospitals and included consecutive adults who presented with a Glasgow Coma Scale (GCS) score of 13-15 after head injury." The study included 3,121 patients with a mean age of 38.7 years.
A wording difference to know about
The abstract words three of the high-risk findings differently from Magent's calculator. It lists "suspected open skull fracture," "vomiting >2 episodes" and "age >65 years." Magent's record and code use a suspected open or depressed skull fracture, two or more episodes of vomiting, and age 65 or older. This page follows the calculator.
When it's used
Magent's calculator accepts ages 16 to 120, with the caller assigning each finding; the record describes the published inclusion as blunt head trauma with GCS 13-15.
Where it's used
The original study ran in the emergency departments of ten large Canadian hospitals.
Who uses it
In the 2001 study, standardized clinical assessments were done in the emergency department before the CT scan.
Limits of the calculation
- It combines seven yes/no findings. It doesn't examine anyone and doesn't diagnose a brain injury.
- It's the Stiell 2001 Canadian CT Head Rule. It isn't NEXUS, PECARN, CATCH or a pediatric head-CT rule.
- It doesn't take a GCS number. The caller answers whether GCS was below 15 at two hours.
- Dangerous mechanism is the caller's call, using the examples in Magent's record above.
- Age must be 16 to 120.
- This page doesn't say what to do with the result.
Clinical decisions belong to a qualified clinician who knows the patient.
How it differs from related calculators
- Glasgow Coma Scale adds eye, verbal and motor scores into a 3–15 total. The CT Head Rule uses a yes/no answer about whether GCS was still below 15 at two hours, not the total itself.
- NEXUS criteria are about the cervical spine, not the head: five findings that must all be absent.
Glossary
- Minor head injury: in this study, a head injury with a GCS of 13 to 15.
- Basal skull fracture: a fracture at the base of the skull.
- Hemotympanum: blood behind the eardrum.
- Battle's sign: bruising behind the ear.
- Raccoon eyes: bruising around both eyes.
- Amnesia before impact: loss of memory for events just before the injury.
Common mistakes
- Counting one episode of vomiting. The calculator's finding is two or more episodes.
- Using the abstract's wording without checking. The abstract's "vomiting >2 episodes" and "age >65 years" differ from the calculator's two or more and 65 or older.
- Entering a GCS number. The input is a yes/no answer about GCS below 15 at two hours.
- Treating the two groups as a score. There are no points; any single finding makes its group positive.
- Using it for children. The 2001 study included adults, and Magent's calculator accepts ages 16 to 120.
Source
Stiell IG, Wells GA, Vandemheen K, et al. The Canadian CT Head Rule for patients with minor head injury. Lancet. 2001;357(9266):1391-1396. DOI: 10.1016/S0140-6736(00)04561-X
Frequently asked questions
What is the Canadian CT Head Rule?
A 2001 decision rule for minor head injury. Using the calculator's thresholds, it has five high-risk findings (GCS below 15 at two hours, suspected open or depressed skull fracture, signs of basal skull fracture, vomiting two or more times, age 65 or older) and two medium-risk findings (amnesia before impact over 30 minutes, dangerous mechanism). The 2001 abstract words vomiting as ">2 episodes" and age as ">65 years".
When does the Canadian CT Head Rule say a CT is needed?
This page doesn't give disposition advice. It shows how the findings combine; what to do next depends on the clinical context.
What counts as a dangerous mechanism?
Magent's record lists a pedestrian struck by a motor vehicle, an occupant ejected from a motor vehicle, or a fall from more than 3 feet or 5 stairs.
What are the signs of a basal skull fracture?
The record lists hemotympanum, raccoon eyes, cerebrospinal fluid leaking from the ear or nose, and Battle's sign.
Does the Canadian CT Head Rule apply to children?
The 2001 study included adults, and Magent's calculator accepts ages 16 and older. It isn't PECARN or CATCH.
Who developed the Canadian CT Head Rule?
Ian Stiell and colleagues, in a 2001 paper in The Lancet.