From the Guidelines
A CT scan is indicated for headaches when patients meet any of the criteria outlined in the Ottawa SAH Rule, which includes age ≥40 y, neck pain or stiffness, witnessed loss of consciousness, onset during exertion, thunderclap headache, or limited neck flexion on examination. This recommendation is based on the most recent and highest quality study, which is the 2023 guideline for the management of patients with aneurysmal subarachnoid hemorrhage from the American Heart Association/American Stroke Association 1. The Ottawa SAH Rule serves as a method to screen out individuals with a low likelihood of aneurysmal subarachnoid hemorrhage (aSAH), and application of the rule requires that patients who present with a severe headache and meet any of the criteria may need to undergo additional testing, as directed by the treating physician.
Some key points to consider when evaluating patients with headaches include:
- The sensitivity of a noncontrast head CT for detecting SAH is high, especially when performed within 6 hours of symptom onset, with a sensitivity of 98.7% and specificity of 99.9% 1
- The lack of SAH on a noncontrast head CT is likely sufficient to exclude aSAH in patients presenting within 6 hours of headache onset who have no new neurological deficits 1
- CT angiography (CTA) is widely available and often used as the next diagnostic test when SAH is diagnosed with noncontrast CT, but digital subtraction angiography (DSA) is considered the gold-standard modality for evaluating cerebrovascular anatomy and aneurysm geometry 1
- The use of the Ottawa SAH Rule can help identify a subset of patients who are unlikely to have aSAH and thereby avoid additional imaging and workup that use resources and expose patients to unnecessary risk 1
In addition to the Ottawa SAH Rule, other concerning features that may suggest a serious underlying condition and warrant a CT scan include:
- Sudden onset severe headache (thunderclap)
- Headache with fever and neck stiffness
- Headache after trauma
- Headache with neurological deficits (weakness, numbness, vision changes)
- New headache in patients over 50
- Headache that worsens with position changes or Valsalva maneuvers
- Headache in immunocompromised patients
- Headaches that are progressively worsening despite treatment
- New headache pattern different from usual headaches
- Headaches that wake patients from sleep
- History of cancer or HIV
It is essential to note that for most routine headaches without these warning signs, particularly migraines or tension headaches with typical patterns, CT scans are generally not necessary and expose patients to radiation without changing management 1.
From the Research
Indications for CT Scan with Headache
- A CT scan is indicated in patients with a severe, abrupt onset headache, also known as thunderclap headache, to rule out subarachnoid hemorrhage (SAH) 2, 3, 4, 5
- The current standard work-up for thunderclap headache includes a brain CT scan followed by lumbar puncture (LP) if the CT is non-diagnostic in patients with a normal neurological exam 2
- A CT scan may also be indicated in patients with acute severe headache to exclude other secondary causes such as cerebral venous thrombosis, dissection, or reversible cerebral vasoconstriction syndrome 6, 3, 4, 5
Specific Conditions that May Require a CT Scan
- Subarachnoid hemorrhage (SAH) 2, 3, 4, 5
- Cerebral venous sinus thrombosis 6, 3, 4, 5
- Arterial dissection 3, 4, 5
- Reversible cerebral vasoconstriction syndrome 6, 3, 4, 5
- Pituitary apoplexy 3, 4, 5
- Intracranial hemorrhage 3, 4
- Ischemic stroke 3, 4, 5
- Colloid cysts of the third ventricle 3, 4, 5
- Spontaneous intracranial hypotension 3, 4, 5