• Clinical science

Subarachnoid hemorrhage


Subarachnoid hemorrhage (SAH) refers to bleeding into the subarachnoid space. SAH most often results from head trauma, while nontraumatic SAH is most commonly due to the rupture of an aneurysm involving the circle of Willis. SAH typically presents with severe headache, nausea/vomiting, and/or acute loss of consciousness. A fresh intracranial hemorrhage appears hyperdense on a non-contrast CT scan, confirming diagnosis. CT angiography and lumbar puncture may be necessary for further evaluation. Treatment consists of carefully lowering blood pressure and measures to prevent cerebral vasospasm. Clipping or coiling of the bleeding aneurysm may be necessary to prevent potentially fatal rebleeding. SAH is associated with a high mortality as a result of frequent complications such as rebleeding and secondary ischemic strokes due to vasospasm.


  • Traumatic: head trauma is the most common cause of SAH
  • Nontraumatic
    • Peak incidence: around the age of 50
    • > (3:2)
    • Responsible for 5% of all cases of stroke
    • Higher incidence in pregnancy; 6–25% of maternal deaths are due to SAH rupture


Epidemiological data refers to the US, unless otherwise specified.


  • TraumaticTraumatic brain injury
  • Nontraumatic/spontaneous
    • Ruptured aneurysm usually in the circle of Willis
      • Berry aneurysm: (80% of cases of nontraumatic SAH)
        • Highest risk of rupture
        • Round, saccular aneurysms located at major branches of large arteries
        • Multifactorial etiology
      • Fusiform aneurysm: low risk of bleeding
      • Mycotic aneurysm: low risk of bleeding
        • Shape: mushroom-shaped
        • Cause: septic embolisms (mostly due to bacterial endocarditis)
        • Site: small, peripheral segments of cerebral vessels
    • Ruptured arteriovenous malformation (AVM) (10% of cases of nontraumatic SAH)
    • Others: cortical thrombosis, angioma, neoplasm, infection
  • Triggers: most cases unknown, may be triggered by an acute rise in blood pressure (e.g., caffeine consumption, acute anger, physical exertion)
  • Risk factors



World Federation of Neurological Surgeons grading



Clinical features

  • Prodromal symptoms
    • Severe headache (days to weeks prior in > ⅓ of patients) due to a sentinel leak (warning leak); sometimes accompanied with transient diplopia that resolves completely
    • Oculomotor nerve palsy: defective vision with an ipsilaterally fixed, dilated pupil
    • TIAs may occur due to the formation of embolisms in the aneurysm



  • Nonenhanced CT (best initial test ): shows blood in subarachnoid space
  • Lumbar puncture (LP), if CT negative
    • ↑↑ RBCs , WBCs , ↑ protein (gamma globulin)
    • Glucose normal
    • ↑ or ↔︎ opening pressure
    • Yellowish (xanthochromia) or red discoloration
  • Angiography
    • Digital subtraction angiography (DSA): determines the site of bleeding/aneurysm (also identifying mycotic aneurysms) preoperatively
    • CT angiography (CTA); : if CT does not confirm SAH in clinically suspected or high-risk cases (emergent or unstable patients)
    • MRI with or without angiography : consider if no lesion found with other angiography methods
  • Additional baseline tests in all patients
    • Chest x-ray: to exclude pulmonary complications (e.g., pulmonary edema)
    • Serum troponin in all patients: predicts neurological complications and outcome
    • ECG: to exclude myocardial ischemia (e.g., ↓ left ventricular function)



Initial treatment

  • Control blood glucose levels

Definitive treatment

  • Surgical clipping (treatment of choice) and/or endovascular coiling (increasingly used alternative for poor surgical candidates) should be performed early to prevent rebleeding
  • If hydrocephalus is present → ventricular drain, serial LPs, or permanent ventriculoperitoneal shunt

Use of nitrates should be avoided since they may raise ICP!




We list the most important complications. The selection is not exhaustive.


  • 50% mortality rate within the first 30 days
  • Survivors: increased rates of neurologic impairment (e.g., cognitive, mood changes, functional, epilepsy) and increased risk of recurrent SAH
  • 10% of patients die before they can be brought to the hospital and another 10% die during the first 24 hours (30-day mortality is approximately 35%).