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:


A recent systematic review in JAMA found the following likelihood ratios for serious intra-cranial abnormality in patients presenting with headache:

Table 1 Likelihood ratios for serious intra-cranial abnormality
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:

  1. age ≥40 years
  2. neck pain or stiffness
  3. witnessed loss of consciousness
  4. onset during exertion
  5. “thunderclap headache” (ie. instantly peaking pain)
  6. limited neck flexion on examination