Nonaneurysmal subarachnoid haemorrhage

Approximately 75% of patients who suffer a non-traumatic, spontaneous SAH will be found to have a cerebral aneurysm.83 An AVM will be discovered in another 5%. Twenty per cent of SAH patients will have various other causes to which the haemorrhage is attributed. When the initial angiogram does not demonstrate an aetiology, further investigation with MRI and CT angiography is warranted. While past studies have found that a significant number of patients with initially negative arteriograms had an aneurysm ultimately demonstrated on a second angiogram or at autopsy, the use of repeat angiography is controversial.84-86 As angiographic techniques have improved, the yield of repeat angiography has decreased. Forster reported only one patient in whom a second angiogram diagnosed a previously occult cerebral aneurysm out of 56 SAH patients with initially negative studies.87 Others have reported higher diagnostic yields of 3-22%.88-93 It has been our policy to tailor each diagnostic evaluation to the patient's specific findings. If the initial angiogram fails to demonstrate a cause of the SAH but shows focal vasospasm, the angiogram is repeated five to seven days later. We also advocate repeat angiography if a portion of the cerebral vasculature is not adequately visualised on the initial study or in patients who have a large amount of subarachnoid blood visualised on CT scanning.

The differential diagnoses that must be considered in cases of non-aneurysmal SAH are extensive. Trauma is the most frequent cause of non-aneurysmal SAH and at times it can be difficult to determine if the SAH was the result or the cause of the patient's injuries. Other aetiologies include angiographically demonstrable and angiographically occult vascular malformations and arteriovenous fistulas, coagulopathies, granulomatous angiitis, venous thrombosis, small arterial and venous tears, central nervous system infection, intra- and extra-axial tumours, hypertension, drug abuse, and various aetiologies within the spinal canal.94-96 SAH of spinal origin occurs most commonly from spinal AVMs.

The management goals in spontaneous SAH are similar to those in patients with head trauma, namely diagnose the condition and minimise the potential for further injury. The treatment of SAH of unknown aetiology is aimed at preventing secondary injury and providing relief of symptoms. Patients are initially placed on bedrest under close observation. Blood pressure is controlled with antihypertensives and the patients are well hydrated. Headache and cervical pain are treated with analgesics as needed and prophylactic anticonvulsants are administered. Corticosteroids, in the form of dexamethasone 4 mg every six hours, are used to alleviate symptomatically signs of blood induced meningitis. While symptomatic vasospasm occurs in a small percentage of patients who present with SAH of undetermined aetiology, we administer an oral calcium channel blocking agent, nimodipine, 60 mg every four hours, to reduce the effects of cerebral vasospasm, should it occur. The incidence of vasospasm is less than in those patients found to have aneurysmal SAH and may be related to the magnitude of the haemorrhage seen on the presenting CT scan.89 We have observed angiographic vasospasm in non-aneurysmal SAH, although clinically symptomatic vasospasm in this specific group of patients is rare in our experience. The treatment of symptomatic vasospasm will be discussed further in the following section on aneurysmal SAH.

Patients who present with non-aneurysmal SAH are typically in better neurological condition than those patients with SAH from ruptured aneurysms.97-100 Although the source of SAH remains undiscovered in 20% of patients, the mortality rate for this group of patients is less than 3%. The incidence of rebleeding is 4% in the first six months and ranges from 02% to 0 86% per year after six months.101 The outcomes of a number of reported series concerning SAH with negative angiography have found that 80% of patients with SAH of undetermined aetiology will have a good outcome and return to gainful employment, as opposed to less than 50% of patients who survive aneurysmal SAH.83,100 The patient's clinical status usually corresponds to the amount of subarachnoid blood present on the CT scan.90 The magnitude of the haemorrhage seen on CT scan relates to the development of complications secondary to the haemorrhage. These complications include cerebral vasospasm, hydrocephalus, seizures, memory disturbances, headache, and psychological disturbances. Stober has reviewed the blood distribution on CT scans following both aneurysmal and non-aneurysmal SAH and determined that SAH of unknown aetiology is unlikely to result in blood in the Sylvian or interhemispheric fissures.102 The interpeduncular or perimesencephalic cisterns often demonstrate focal blood collections when SAH of unknown aetiology occurs.43,103,104

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