A subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space surrounding the brain, i.e., the area between the arachnoid and the pia mater. It may arise due to trauma or spontaneously, and is a medical emergency which can lead to death or severe disability even if recognized and treated in an early stage.
Symptoms and causes
SAH can result from head trauma, the most common cause, or may occur spontaneously. Spontaneous SAH most commonly follows the rupture of a cerebral aneurysm or cerebral arteriovenous malformation, but can also be due to angioma, thrombosis, hematoma, or brain tumor.
SAH in a trauma patient is often detected when a patient who has been involved in an accident becomes less responsive or develops hemiplegia (one-sided weakness) or changed pupillary reflexes, and Glasgow Coma Score calculations deteriorate. Headache is not necessarily present.
In contrast to other types of headaches, which have slower onsets, the headache of SAH is sometimes called a "thunderclap headache". It is often described as the worst headache the victim has ever had. Neurological symptoms (like slurred speech, paralysis, and visual symptoms) and meningism are not necessarily present, but nausea, vomiting and loss of consciousness are often seen.
Aneurysm related SAH has a 50% pre-hospital mortality, highlighting the significant nature of the hemorrhage.
The diagnosis is made by the clinical history, physical examination, and CT scanning. The scan may reveal blood in the sub-arachnoid space, cerebral ventricles or brain parenchyma, depending on the size and location of the bleed. In traumatic SAH (tSAH), the scan may also identify any additional intracranial injuries. Lumbar puncture may be needed for diagnosis in small subarachnoid bleeds that may not be detected on CT scans; the presence of xanthochromia -- a yellow tinge to the cerebrospinal fluid consequent to breakdown of blood -- is indicative of SAH, whereas gross blood may merely indicate a traumatic lumbar puncture. Cerebral angiography can isolate the source of bleeding prior to surgical treatment.
Neurosurgical intervention is necessary in severe or traumatic SAH, especially in the case of high or increasing Hunt-Hess scoring. This may be by craniotomy and external clipping of the bleeding vessel or aneurysm, or by interventional radiology (neuroradiology), which employs transfemoral angiography and inserting of metal coils to stem the bleeding (which is especially useful in aneurysmatic hemorrhage).
In case of spontaneous rupture of aneurysm, there are few evidence-based guidelines on the timing of neurosurgical interventions, and this often depends on the clinical experience and guidelines of local interventional centers. There is, however, a risk of re-rupture of the aneurysm and most experts favor intervention as soon as the appropriate operating room and personnel resources can be mobilized.
Medical treatment is available to both reduce the risk of repeat bleeding, and to treat a serious complication of SAH called vasospasm. In the case of spontaneous SAH from an aneurysm, there is a significant risk of repeat bleeding until definitive surgical intervention can be performed. During this waiting period medical treatments to control blood pressure, bed rest, and a quiet environment reduce the risk of rebleed.
Vasospasm is a serious complication of SAH. It may be seen in 50% of SAH patients studied with angiography, and is symptomatic roughly 30% of the time. This condition can be verified by transcranial doppler or cerebral angiography, and can cause ischemic brain injury which can cause permanent brain damage, and if severe can be fatal. Nimodipine is an oral calcium channel blocker, that has been shown to reduce the chance of a bad outcome, even if it does not significantly reduce the amount of angiographic vasospasm.
A patient who recovers without immediate intervention may receive follow-up angiography to identify aneurysms which may be amenable to coiling to prevent recurrent episodes of SAH.