Subarachnoid Hemorrhage

Contributed by: Yousuf Qaseem, University of New Mexico School of Medicine, 1 University of New Mexico, Albuquerque, NM 87131
Overview
  • Subarachnoid hemorrhages are a subtype of intracranial hemorrhage due to arterial bleeding between the brain parenchyma and arachnoid mater. They typically present as a rapid onset severe headache and are a neurological emergency with grave clinical sequelae if left untreated.
Etiology
  • Subarachnoid hemorrhages most often result from traumatic head injury and/or rupture of a saccular (berry) aneurysm. Up to 2% of adults in the United States have asymptomatic saccular aneurysms which are generally located at large vessel bifurcations with 85% in the anterior circulation. Larger aneurysms are at increased risk for rupture.
Diagnosis
  • As with other forms of intracranial hemorrhage, a non-contrast head CT is necessary for evaluation and characterization of the hemorrhage. Subarachnoid hemorrhages are often more difficult to identify on imaging than other types of intracranial hemorrhage. Classically, the appearance is of bright white blood that often tracks into the basal cisterns.
  • If the head CT is non-diagnostic, a lumbar puncture can be performed that demonstrates xanthochromia, a yellow appearance of the cerebrospinal fluid secondary to blood accumulation in the CSF.
Clinical Features and Consequences
  • The classic description of subarachnoid hemorrhage is that of the “worst headache of my life”. The headache is of sudden-onset with rapid progression to maximal severity. Neck stiffness due to irritation of the meninges by blood as well as nausea and vomiting are common. Depending on the location of the hemorrhage, focal neurological deficits such as weakness or numbness may also occur.
  • It is important to note that subarachnoid hemorrhage carries a risk of ischemic stroke secondary to cerebral vasospasm, peaking at approximately 7 days post-hemorrhage. For this reason patients are typically treated with a calcium channel blocker to prevent vasospasm. Subarachnoid hemorrhage may also result in significant hyponatremia due to natriuresis and volume depletion. If the aneurysm is not identified and surgically repaired, re-bleeding may occur within the weeks or months following initial rupture.

Further Reading
  • Naidech AM. 2011. "Intracranial Hemorrhage." American Journal of Respiratory and Critical Care Medicine 184.9 (2011): 998-1006


To cite this article
  • Qaseem, Y, “Epidural Hematoma” in Pathway Medicine: An Introduction to Clinical Medicine", PathwayMedicine.org (2017).