Who Needs a CT Scan
Ultimately, this is a decision that must be based on the:
- Presentation of the patient
- Experience and knowledge of the attending doctor
However, there is no justification for scanning all headaches.
A number of studies have approached the question of which headache patients require CT scanning:
JAMA
A recent systematic review in JAMA found the following likelihood ratios for serious intra-cranial abnormality in patients presenting with headache:
| Headache Characteristic | Likelihood Ratio of Serious Intra-cranial Pathology |
| Abnormal findings on neurologic examination | 5.3 |
| Headache aggravated by exertion or a Valsalva-like manoeuvre | 2.3 |
| Headache with vomiting | 1.8 |
The Ottawa SAH Rule can potentially help to rule out SAH in patients with acute nontraumatic headache reaching maximum intensity within 1 hour and a normal neurologic examination. In the study population, it had 100% (95% CI, 97.2%-100.0%) sensitivity and 15.3% (95% CI, 13.8%-16.9%) specificity.
The Rule states that in patients meeting the inclusion criteria, SAH was ruled out in the absence of4:
- age ≥40 years
- neck pain or stiffness
- witnessed loss of consciousness
- onset during exertion
- “thunderclap headache” (ie. instantly peaking pain)
- limited neck flexion on examination