Subarachnoid Hemorrhage

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Diagnosis and reasoning

This patient was woken up by an acute severe headache : a typical "thunderclap" headache. This should be assumed to be due to a subarachnoid hemorrhage (SAH) until proven otherwise. The other life threatening conditions which may present with an acute headache include intracerebal hemorrhage, cervical arterial dissection, acute hypertensive crises, pituitary apoplexy and intracranial infections. Unfortunately, it is impossible to reliably differentiate between these etiologies on clinical grounds alone. A CT scan of the brain is a good first line diagnostic test, but turns out to be negative in this patient. As a lumbar puncture may yield useful information, this should be performed next. The CSF analysis shows the presence of a large number of erythrocytes (red blood cells), which is supportive of an SAH. However, it should be kept in mind that a traumatic lumbar puncture may result in contamination of the CSF with blood, yielding a similar microscopic appearance. CSF spectrophotometry demonstrates the presence of xanthochromia - a characteristic yellowish discoloration caused by the presence of significant quantities of bilirubin (which is a byproduct of erythrocyte lysis). This is virtually pathognomonic of a subarachnoid hemorrhage. Note that bilirubin in the systemic circulation cannot enter the CSF as the blood brain barrier is impermeable to bilirubin. As SAH is often secondary to rupture of a vascular aneurysm, further evaluation via cerebral angiography is mandatory. This patient is found to have an aneurysm in the region of the anterior communicating artery. Nimodipine will reduce the risk of delayed ischemia, while endovascular coil placement will prevent rebleeding from the aneurysm. Sumatriptan is indicated in patients with migraine - and should be avoided in SAH, as it may cause cerebral vasospasm. IV antibiotics are not required immediately (but may be required prophylactically if surgery is performed later).


Discussion

SAH is a neurological emergency characterized by extravasation of blood into the subarachnoid space, and causes approximately 5% of strokes. Almost half of patients are < 55 years of age. Between 80% to 85% of SAHs are due to rupture of an intracranial aneurysm ("aneurysmal SAH"). These aneurysms are acquired in origin, and arise due to hemodynamic stress at sites of arterial branching. In accordance with the law of Laplace, as the radius of the vessel wall increases, the tension required to withstand a given blood pressure increases correspondingly. This sets up a vicious cycle where aneurysmal dilation leads to further wall stress and even more dilation. The risk factors for SAH may be classified into modifiable and non-modifiable categories. The major modifiable risk factors include smoking, hypertension and heavy alcohol use, all of which roughly double the risk. Non modifiable risk factors include a family history of SAH and heritable connective-tissue disorders such as polycystic kidney disease, Ehlers-Danlos syndrome, pseudoxanthoma elasticum, and fibromuscular dysplasia. The most characteristic symptom of SAH is a severe headache of sudden onset ("thunderclap headache"). The onset is usually within a few seconds, while patients may describe the headache as being "the worst headache they have ever experienced". Note that it is the suddent onset which is the key diagnostic feature, as it suggests a vascular etiology. However, patients often neglect to mention this unless directly asked. Photophobia and neck pain may occur due to an inflammatory response to blood in the subarachnoid space. In addition, many patients experience fever, nausea and vomiting. Almost two-thirds of patients have depressed consciousness or frank coma at the time of admission. Some revert to a normal level of consciousness afterwards, while others persist in the same state or deteriorate further. If further deterioration occurs, acute hydrocephalus formation or rebleeding should be considered. Note that between 30% to 50% of these patients experience a minor bleed 7 to 20 days before a major SAH. This minor bleed is usually manifested by a sudden and severe headache termed a "sentinel headache". The examination may show signs of meningeal irritation. Focal neurological deficits may be present and may be due to focal ischemia, or less often, due to bleeding into the cerebral parenchyma. Fundoscopy may show flame-shaped hemorrhages (secondary to central retinal vein obstruction due to increased CSF pressure). Cranial nerve palsies may occur due to aneurysmal compression. Non contrast CT scanning is the initial investigation of choice, and if performed within one day of onset identifies extravasated blood in 95% of patients. However, this proportion falls rapidly afterwards (to only 58% by day five), as the blood is absorbed and cleared from the subarachnoid space. In a minority of these patients, the CT scan may be normal - in which case a lumbar puncture should be performed, with the presence of CSF xanthochromia indicating that blood has been present for at least 2 hours in the CSF. If the lumbar puncture is performed too early, xanthochromia may be absent - thus it is preferably deferred for at least six hours after onset of symptoms. Angiography allows identification of the causative aneurysm and visualization of the surrounding anatomy. CT angiography is widely used for this purpose and may be performed immediately after the CT brain, while the patient is still in the scanner. Magnetic resonance angiography (MRA) is radiation free and does not require contrast. However, the longer duration and difficulty in monitoring patients undergoing the procedure precludes its use in confused or unconscious patients. The initial management of these patients includes resuscitation and stabilization followed by bedrest and continuous observation. Other key elements of the management include adequate analgesia (which may require opioids), venous thromboembolism prophylaxis, blood pressure control and prevention and treatment of neurological and systemic complications. Antiepileptic therapy is indicated in patients who experience seizures. Many units also have the policy of commencing prophylactic antiepileptic therapy in all patients (as there is fear that a seizure will increase intracranial pressure and precipitate rebleeding). Certain units may also have a policy of administering steroids (especially if surgery is likely), although their use is controversial. The main neurological complications of aneurysmal SAH are delayed cerebral ischemia, hydrocephalus and rebleeding. Reactive vasospasm is believed to be the main causative agent of cerebral ischemia, although hypovolemia and hypotension may also play a role. Calcium antagonists (i.e. nimodipine) have been shown to improve the outcome in such patients. Acute hydrocephalus may present as a progressive reduction in consciousness, with associated downward deviation of the eyes and small non-reactive pupils, with repeated CT scanning required for diagnosis. Almost 40% of these patients will develop rebleeding if no interventions are performed. In addition, almost 80% of patients with rebleeds die or remain disabled. Thus endovascular or neurosurgical intervention should be considered if at all possible. Endovascular occlusion (by packing the aneurysm with platinum coils) is currently the intervention of choice, but is difficult to perform in certain anatomical configurations. Surgical clipping and occlusion of the aneurysm is the other major management option. Systemic complications are common in these patients and include fever, hypertension/hypotension, hyperglycemia, electrolyte abnormalities, cardiac arrythmias and heart failure, pulmonary edema and pneumonia. Of patients who survive a SAH, between half to two-thirds are able to return to work one year afterwards. However, many of them report problems with memory, mood, or neuropsychological function.


Take home messages

  1. SAH is an important cause of stroke in younger patients.
  2. The sudden onset is the diagnostic feature which suggests a vascular etiology for the headache.
  3. Non-contrast CT is the investigation of choice. If this is negative, lumbar puncture should be considered.
  4. Lumbar puncture is preferably delayed for at least 6 hours following onset of symptoms.
  5. The major neurological complications are delayed ischemia, acute hydrocephalus and rebleeding.
  6. If interventions are not performed, rebleeding occurs in 40% of patients and is associated with a poor prognosis.

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  1. BMJ: Easily missed? Subarachnoid haemorrhage (2009)
  2. BMJ: Investigating suspected subarachnoid haemorrhage in adults (2011)
  3. BMJ: Subarachnoid haemorrhage (2006)
  4. Lancet: Subarachnoid haemorrhage (2007)
  5. NEJM: Aneurysmal Subarachnoid Hemorrhage (2006)
  6. Stroke: Incidence and Significance of Early Aneurysmal Rebleeding Before Neurosurgical or Neurological Management (2001)