Subarachnoid hemorrhage (SAH) is a neurologic emergency due to bleeding into the subarachnoid space. Mortality can reach 50%. The clinical presentation is most often in the form of headache, classically defined as maximal at onset and worst of life. The most common cause is traumatic; approximately 80% of nontraumatic SAH are due to aneurysmal rupture, with the remainder from idiopathic peri-mesencephalic hemorrhage or other less common causes. (Long et al, 2017) Acute SAH from a ruptured intracranial aneurysm contributes for 30% of all hemorrhagic strokes, but it can be also secondary to inflammatory events. (Schneider et al, 2018)
Although its overall incidence is less than that of acute ischemic stroke, sub-arachnoid hemorrhage carries increased risks of both mortality and disability. (Boiling & Groves, 2019) The incidence has decreased over past decades, possibly in part related to lifestyle changes such as smoking cessation and management of hypertension. The clinical presentation varies, but severe, sudden onset of headache is the most common symptom, variably associated with meningismus, transient or prolonged unconsciousness, and focal neurological deficits including cranial nerve palsies and paresis. (Claassen & Park, 2022)
When a clinical suspicion for SAH exists based on history and physical exam, non-contrast computed tomography (CT) is the first diagnostic tool. At the onset of the bleed, subarachnoid blood is the most readily visible on CT, but it becomes more difficult to appreciate as red blood cell (RBC) degradation progresses. Advances in neuroimaging have increased the sensitivity of non-contrast CT, raising questions regarding the need for lumbar puncture (LP) in the face of a negative CT. If non-contrast head CT is not definitive (time to study, patient elements [i.e., severe anemia], interpretation limitations [i.e., trainee radiologist, motion artifact], etc) the next recommended diagnostic tool is the LP. Once the diagnosis of SAH is established, the most important time-sensitive goals include confirmation of airway security and stabilization of hemodynamics. (Marcolini et al, 2019)
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