September 24, 2020
An 81-year-old woman presented to the emergency department due to a fall from standing with a brief loss of consciousness lasting 30–60 seconds.
Perimesencephalic Subarachnoid Hemorrhage (PMSAH)
- Background:
- Incidence is estimated at 0.5 per 100,000 people per year and accounts for about 5% of all subarachnoid hemorrhages.
- Bleeding is thought to be from low-pressure venous origin due to the limited extension of blood and low rate of subsequent rebleeding.
- Clinical Presentation:
- The most common complaint is a headache usually starting within minutes compared to seconds with an aneurysmal rupture. Patients usually present with a Glasgow Coma Scale score of 15, oftentimes associated nausea and vomiting, and rarely loss of consciousness of approximately less than 1 minute.
- Can clinically mimic an aneurysmal subarachnoid hemorrhage; therefore, it is important to distinguish between the two
- Key Diagnostic Features:
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PMSAH, as opposed to aneurysmal SAH, is classically located in the lateral basal cisterns, primarily involving the quadrigeminal cistern, ambient cistern, and cerebellopontine angle cistern. It may secondarily extend into the remaining basal cisterns.
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CTA should be performed to rule out aneurysmal rupture as a cause of the bleeding due to high mortality from an aneurysmal bleed.
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MRV may be considered if venous sinus thrombosis is suspected.
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- Differential Diagnoses:
- Aneurysmal subarachnoid hemorrhage
- Dural venous sinus thrombosis
- Cerebral vascular malformation
- Thorough investigation including conventional angiography is required to exclude the above-listed causes of SAH.
- Treatment:
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Treatment is usually supportive.
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Rebleeding is rare and life expectancy is usually not affected.
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Death is rare from PMSAH.
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