Snapshot A 45-year-old woman presents to the emergency room with a severe headache of acute onset. Her headache is significantly more severe than her migraine headaches. Her symptoms began approximately 2 hours ago after she was lifting heavy weights. She denies any head trauma, nausea, or vomiting. Physical examination is unremarkable. A CT head without contrast is normal. An emergency lumbar puncture is done and demonstrates elevated red blood cells that do not diminish from tube 1 to 4. Introduction Definition bleeding into the subarachnoid space, where cerebrospinal fluid (CSF) is housed Epidemiology risk factors cigarette smoking (most important preventable risk factors) hypertension polycystic kidney disease Etiology aneurysm rupture can result from an acute trigger, such as physical exertion may occur in the absence of an acute trigger, such as in sleep Pathogenesis rupture of an aneurysm (most commonly a saccular aneurysm) leads to the release of blood into the CSF under arterial pressure rapid filling of blood within the CSF leads to increased intracranial pressure Presentation Symptoms thunderclap headache a sudden and severe headache, often described as "the worst headache of my life" increased intracranial pressure nausea vomiting meningismus neck stiffness Imaging CT head without contrast indication imaging study of choice in patients with suspected subarachnoid hemorrhage findings hyperdensities in the suprasella cisterns extending peripherally Studies Lumbar puncture indication when CT head without contrast is normal and there is still suspicion for a subarachnoid hemorrhage > 6 hours from symptoms onset findings elevated red blood cell count that does not decrease from collecting tube 1 to 4 xanthochromia Differential Reversible cerebral vasoconstriction syndrome (RCVS) differentiating factors recurrent thunderclap headaches normal neuro imaging but can demonstrate border zone infarcts or vasogenic edema abnormal cerebral angiography Treatment Medical nimodipine indication prophylaxis to reduce the risk of delayed cerebral ischemia Operative aneurysm repair indication to prevent re-rupture of the aneurysm Complications Arterial vasospasm Hydrocepalus Hyponatremia Cerebral salt wasting can be seen after any CNS trauma polydipsia, polyuria, high urine sodium, and hyponatremia