Subarachnoid hemorrhage natural history, complications and prognosis

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Sara Mehrsefat, M.D. [3]

Natural history

Following rupture of an aneurysm, the blood directly release into the cerebrospinal fluid (CSF) under arterial pressure. As the blood spreads quickly into the CSF, it rapidly increasing intracranial pressure.

Depending on the location of the aneurysm, the blood can spread into:

• Intraventricular space
• Brain parenchyma
• Subdural space

The bleeding usually lasts only a few seconds. However, rebleeding can be considered as one of the complication which can occur within the first day.

Complications

Complications of SAH can be acute, subacute, or chronic.

• Acute:
  • Coma and brainstem herniation due to increased intracranial pressure (ICP)
  • Pulmonary edema ("neurogenic pulmonary edema") as a result of the suddenly increased ICP
  • Cardiac arrhythmias and myocardial damage
  • Hydrocephalus, which may also happen in the subacute time frame
• Subacute:
  • Vasospasm, leading to ischemia of the brain
  • Hyponatremia (low sodium levels) - due to SIADH or cerebral salt wasting syndrome
• Chronic:
  • Long-term immobility
  • Pneumonia and pulmonary embolism (due to immobility)
  • SAH recurrence (20% within two weeks if the aneurysm is not secured by clipping or coiling)
  • Persistent neurologic deficits

Prognosis

Nearly half the cases of SAH are either dead or moribund before they reach a hospital. Of the remainder, a further 10-20% die in the early weeks in hospital from rebleeding. Delay in diagnosis of minor SAH without coma (or mistaking the sudden headache for migraine) contributes to this mortality. Patients who remain comatose or with persistent severe deficits have a poor prognosis.

After the SAH is treated the patients can experience prolonged, even permanently reoccurring headaches.