Subarachnoid Hemorrhage

Subarachnoid Hemorrhage: A subarachnoid hemorrhage is sudden bleeding into the subarachnoid space between the pial and arachnoid membranes of the brain. While the mechanism of action is often thought of as rupture of a cerebral aneurysm or arteriovenous malformation, trauma is actually the most common mechanism. Prompt recognition and treatment are required as the mortality rate at one week is almost 40%.

Epidemiology:  Roughly 80% of subarachnoid hemorrhages occur in patients older than 40 years. Although more common in men (incidence ratio of 3:2), during the third trimester of pregnancy woman are at increased risk. About 20,000-30,000 new cases are diagnosed in the United States each year.

Risk Factors: Smoking is the most important reversible risk factor for subarachnoid hemorrhage. Hypertension and alcohol are also significant risk factors.

Symptoms: A sudden and severe headache, facial pain, double vision. Physical exam may also reveal retinal hemorrhages and meningismus.

Differential Diagnosis: TIA, Migraine Headache, Cluster Headache, Meningitis, Encephalitis, Hypertensive Emergency.

Investigations: The diagnosis of a subarachnoid hemorrhage can usually be made with a CT scan. If the CT scan is not conclusive, a lumbar puncture may be done to confirm or rule out the diagnosis.

Treatment: Both the prognosis and treatment of subarachnoid hemorrhage is dependent on the level of consciousness of the patient, the age, and amount of blood seen on imaging. Patients will be admitted to the ICU with the goals of reducing intracranial pressure, reducing the risk of rebleeding, providing venous thromboembolism prophylaxis, and if necessary transferred to surgery. Vasospasm is the major complication and the risk may be reduced by nimodipine, a calcium channel blocker.
Imaging Findings
- Defined as blood between the pia and the arachnoid membrane
- Can cause acute hydrocephalus from clot, delayed hydrocephalus from arachnoid granulation scarring, or vasospasm (peaks 7-10 days after injury)
- Best seen as hyperdensities on non-contrast CT, and MR FLAIR
- Hyperintense on T1, isointense on T2; DWI can show restricted diffusion in ischemic areas if reactive vasopasm
- Can be focal in distribution, in several sulci, or more diffuse layering over tentorium or found in basal cisterns
- Hyperdense blood in interpeduncular cistern may be only manifestation
- Associated with trauma: soft tissue injury, cerebral contusion, epidural and subdural hematomas, and diffuse axonal injury
- If no trauma consider workup for cerebral aneurysm or arteriovenous malformation



Case #1a. Noncontrast CT of head: hyperattenuating blood in basal cisterns, midline, and sulci.

Case #1b. Noncontrast CT: Blood also seen in left sylvian fissure. Asymmetric SAH.