A 48-year-old male with no past medical history was lifting weights at the gym when he felt a “pop” in the back of his head immediately followed by a 10/10 holocephalic headache. He was nauseated and had one episode of emesis but retained normal consciousness. He was brought to the emergency department via EMS, and on arrival his vitals were within normal limits. His neurologic examination was normal with the exception of nuchal rigidity. A head CT was completed shortly after arrival. The only abnormalities demonstrated on the head CT are shown in the figure that follows. A CTA was completed which was negative for an aneurysm or vascular malformation.
Which of the following is consistent with findings presented?
Correct Answer: C
The differential diagnosis for subarachnoid hemorrhage is broad, including aneurysm, trauma, vascular tumors, dural arteriovenous fistula, and arteriovenous malformation. The head CT above demonstrates an isolated perimesencephalic subarachnoid hemorrhage. Although less common than the typical basilar subarachnoid hemorrhage, perimesecephalic subarachnoid hemorrhage can be the result of an arterial aneurysm (typically verterbrobasilar), but 95% are idiopathic despite extensive evaluation. Patients presenting with isolated perimesencephalic subarachnoid hemorrhage appear similar with thunderclap headache, nausea, emesis, but typically do not have a loss of consciousness or decreased level of consciousness. Despite CT angiograms being negative, they will undergo typically multiple digital subtraction angiograms to evaluate for an underlying vascular lesion and/or aneurysm. There is no standard of care practice on evaluation of perimesencephalic subarachnoid hemorrhage, but personal practice includes angiogram at the time of presentation and then at day 7 of hospitalization as small aneurysms may collapse at the time of rupture, and allowing for an extended time interval to pass it may reexpand. This type of subarachnoid hemorrhage has lower rates of complications than other subarachnoid hemorrhages including vasospasm and hydrocephalus. Although there is no definitive etiology for perimesencephalic subarachnoid hemorrhage, it is thought to be due to a venous tear and hemorrhage rather than arterial.
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