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 is a medical emergency which, depending on severity, 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.

In spontaneous SAH, the cardinal symptom is sudden severe headache, described by patients as "like being hit over the head with a heavy object". In contrast to other types of headaches which have slower onsets, the headache of SAH is sometimes called a "thunderclap headache". Neurological symptoms (like slurred speech, paralysis, visual symptoms and meningism) are not necessarily present, but nausea and vomiting are often seen.

Diagnosis

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. Cerebral angiography can isolate the source of bleeding prior to surgical treatment.

Classification

The Hunt and Hess scale (1968) of subarachnoid hemorrhage severity is:

• Grade 1: Asymptomatic; or minimal headache and slight nuchal rigidity.
• Grade 2: Moderate to severe headache; nuchal rigidity; no neurologic deficit except cranial nerve palsy.
• Grade 3: Drowsy; minimal neurologic deficit.
• Grade 4: Stuporous; moderate to severe hemiparesis; possibly early decerebrate rigidity and vegetative disturbances.
• Grade 5: Deep coma; decerebrate rigidity; moribund.

Treatment

Neurosurgical intervention is necessary in severe SAH with high or increasing Hunt-Hess scoring. This may be by craniotomy and external clipping of the bleeding artery, or by interventional radiology, which employs angiography and inserting of metal coils to stem the bleeding. 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. Some experts favor a "wait-and-see" management in less severe cases.

Medical treatment involves absolute bedrest with the head slightly elevated to encourage venous flow away from the area of the hemorrhage. Some centers are trying the "Triple H treatment", hypertensive hypervolemic hemodilution, which is hoped to minimize continuing bleeding. 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.

Complications

Complications of SAH can be acute, subacute, and chronic.

• Acute:
  • Coma and brainstem herniation due to increased intracerebral pressure (ICP)
  • Pulmonary edema ("neurogenic pulmonary edema") as a result of the suddenly increased ICP
• Subacute:
  • Vasospasm, leading to ischemia of the brain (can be prevented partially with the calcium channel antagonist nimodipine)
  • Hyponatremia (low sodium levels) - due to SIADH or cerebral salt wasting syndrome
• Chronic:
  • Long-term immobility
  • Pneumonia and pulmonary embolism (due to immobility)
  • SAH recurrence (20% within two weeks)

External links

• Emedicine (http://www.emedicine.com/NEURO/topic357.htm) article on SAH
• Neuroland (http://neuroland.com/cvd/sah.htm) SAH page

Reference

• Hunt WE, Hess RM. Surgical risk as related to time of intervention in the repair of intracranial aneurysms. J Neurosurg 1968;28:14-9. PMID 5635959.