SAH: Should we CT, CTA or LP?

  • Headache is a chief complaint that accounts for 2% of emergency department (ED) visits.
  • SAH 1% of headache (2%).
  • Commonly due to ruptured aneurysm.
  • symptoms: Rapid onset of headache, worst of life headache, exertional headache, syncope with headache, vomiting, and neck stiffness are red flags associated with a higher pretest probability of SAH.

How bad?

With 25% mortality within 2 hours of initial bleeding and 40% mortality at one week, missing this diagnosis can be deadly.

Recommendation(long time ago)

ACEP + AHA : CT follow by LP( to look for xantochromia) if CT (-ve)

But ACEP guideline is on 2008.

What about current ACEP Clinical Policy?

Dr. Edlow, one of the editors for the official policy, states that the EM practice should change in that the neurologically intact patient with a sudden, severe headache who undergoes a non-contrast head CT within 6 hours of headache onset no longer requires LP.

The Importance of Test threshold

Definition “at what threshold does further testing do more harm than good?

So, A miss rate of 1% in many diseases is deemed acceptable.

With cerebral hemorrhage accounting for 6%-7% of headaches, and an assumed non-contrast head CT sensitivity of 90%, a negative head CT provides a 0.5% chance of missed SAH.

Many EM physicians advocate that a physician does not rule out disease, but rather, risk stratifies.

Thus, a negative head CT in a patient with headache within six hours does not rule out SAH, but risk stratifies the patient to less than 1% of having SAH.

Risk and the Shared Decision Making Model

Patient + physician = Team

A negative LP and CT can rule out SAH, but LP is associated with patient pain, consumption of valuable time in the ED, and potential difficulty obtaining CSF results if the patient has poor body habitus and/or cooperation.61


Within 6 hours of headache onset, a CT only approach does have literature support for risk stratifying patients to less than 1% risk of SAH. However, after 6 hours, the sensitivity of non-contrast head CT decreases. A test threshold of 1% does seem acceptable currently. Ultimately, a shared decision making model should be followed.


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