A lumbar puncture in progress. A large area on the back has been washed with an iodine-based disinfectant leaving brown coloration As only 10 percent of people admitted to the emergency department with a thunderclap headache are having an SAH, other possible causes are usually considered simultaneously, such as meningitis, migraine, and cerebral venous sinus thrombosis. Intracerebral hemorrhage, in which bleeding occurs within the brain itself, is twice as common as SAH and is often misdiagnosed as the latter. It is not unusual for SAH to be initially misdiagnosed as a migraine or tension headache, which can lead to a delay in obtaining a CT scan. In a 2004 study, this occurred in 12 percent of all cases and was more likely in people who had smaller hemorrhages and no impairment in their mental status. The delay in diagnosis led to a worse outcome. In some people, the headache resolves by itself, and no other symptoms are present. This type of headache is referred to as "sentinel headache", because it is presumed to result from a small leak (a "warning leak") from an aneurysm. A sentinel headache still warrants investigations with CT scan and lumbar puncture, as further bleeding may occur in the subsequent three weeks. The initial steps for evaluating a person with a suspected subarachnoid hemorrhage are obtaining a medical history and performing a physical examination. The diagnosis cannot be made on clinical grounds alone and in general medical imaging and possibly a lumbar puncture is required to confirm or exclude bleeding. Imaging The modality of choice is computed tomography (CT scan), without contrast, of the brain. This has a high sensitivity and will correctly identify 98.7% of cases within six hours of the onset of symptoms. A CT scan can rule out the diagnosis in someone with a normal neurological exam if done within six hours. Its efficacy declines thereafter, and magnetic resonance imaging (MRI) is more sensitive than CT after several days. Angiography After a subarachnoid hemorrhage is confirmed, its origin needs to be determined. If the bleeding is likely to have originated from an aneurysm (as determined by the CT scan appearance), the choice is between cerebral angiography (injecting radiocontrast through a catheter to the brain arteries) and CT angiography (visualizing blood vessels with radiocontrast on a CT scan) to identify aneurysms. Catheter angiography also offers the possibility of coiling an aneurysm (see below). In emergency department patients complaining of acute-onset headache without significant risk factors for SAH, evidence suggests that CT scanning of the head followed by CT angiography can reliably exclude SAH without the need for a lumbar puncture. The risk of missing an aneurysmal bleed as the cause of SAH with this approach is less than 1%. Lumbar puncture Xanthochromia versus normal CSF. Lumbar puncture, in which cerebrospinal fluid (CSF) is removed from the subarachnoid space of the spinal canal using a hypodermic needle, shows evidence of bleeding in three percent of people in whom a non-contrast CT was found normal. A lumbar puncture or CT scan with contrast is therefore regarded as mandatory in people with suspected SAH when imaging is delayed to after six hours from the onset of symptoms and is negative. At least three tubes of CSF are collected. If an elevated number of red blood cells is present equally in all bottles, this indicates a subarachnoid hemorrhage. If the number of cells decreases per bottle, it is more likely that it is due to damage to a small blood vessel during the procedure (known as a "traumatic tap"). While there is no official cutoff for red blood cells in the CSF no documented cases have occurred at less than "a few hundred cells" per high-powered field. The CSF sample is also examined for xanthochromia—the yellow appearance of centrifugated fluid. This can be determined by spectrophotometry (measuring the absorption of particular wavelengths of light) or visual examination. It is unclear which method is superior. Xanthochromia remains a reliable ways to detect SAH several days after the onset of headache. An interval of at least 12 hours between the onset of the headache and lumbar puncture is required, as it takes several hours for the hemoglobin from the red blood cells to be metabolized into bilirubin. ECG ECG changes resembling those of an STEMI in a woman who had an acute CNS injury from a subarachnoid hemorrhage. Electrocardiographic changes are relatively common in subarachnoid hemorrhage, occurring in 40–70 percent of cases. They may include QT prolongation, Q waves, cardiac dysrhythmias, and ST elevation that mimics a heart attack. Classification There are several grading scales available for SAH. The Glasgow Coma Scale (GCS) is ubiquitously used for assessing consciousness. Its three specialized scores are used to evaluate SAH; in each, a higher number is associated with a worse outcome. These scales have been derived by retrospectively matching characteristics of people with their outcomes. The first widely used scale for neurological condition following SAH was published by Botterell and Cannell in 1956 and referred to as the Botterell Grading Scale. This was modified by Hunt and Hess in 1968: Grade Signs and symptoms Survival 1 Asymptomatic or minimal headache and slight neck stiffness 70% 2 Moderate to severe headache; neck stiffness; no neurologic deficit except cranial nerve palsy 60% 3 Drowsy; minimal neurologic deficit 50% 4 Stuporous; moderate to severe hemiparesis; possibly early decerebrate rigidity and vegetative disturbances 20% 5 Deep coma; decerebrate rigidity; moribund 10% The Fisher Grade classifies the appearance of subarachnoid hemorrhage on CT scan. Grade Appearance of hemorrhage 1 None evident 2 Less than 1 mm thick 3 More than 1 mm thick 4 Diffuse or none with intraventricular hemorrhage or parenchymal extension This scale has been modified by Claassen and coworkers, reflecting the additive risk from SAH size and accompanying intraventricular hemorrhage (0 – none; 1 – minimal SAH w/o IVH; 2 – minimal SAH with IVH; 3 – thick SAH w/o IVH; 4 – thick SAH with IVH);. The World Federation of Neurosurgeons (WFNS) classification uses Glasgow coma score and focal neurological deficit to gauge severity of symptoms. Grade GCS Focal neurological deficit 1 15 Absent 2 13–14 Absent 3 13–14 Present 4 7–12 Present or absent 5 <7 Present or absent A comprehensive classification scheme has been suggested by Ogilvy and Carter to predict outcome and gauge therapy. The system consists of five grades and it assigns one point for the presence or absence of each of five factors: age greater than 50; Hunt and Hess grade 4 or 5; Fisher scale 3 or 4; aneurysm size greater than 10 mm; and posterior circulation aneurysm 25 mm or more.
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