• A Lagares, P A Gómez, R D Lobato, J F Alén, R Alday, J Campollo, P González, A de la Lama, J C Palomino, and P Miranda.
• Servicio de Neurocirugía, Hospital 12 de Octubre, Madrid.
• Neurocirugia. 2002 Apr 1;13(2):110-9.

IntroductionIdiopathic subarachnoid haemorrhage (ISAH) represents approximately 15-30% of all subarachnoid haemorrhages. On the basis of the diagnostic CT and depending on the location of the subarachnoid bleeding, patients with ISAH may be classified into three groups: a) Patients with normal CT and diagnosis made by lumbar puncture (ISAHNCT); b) patients with a pure perimesencephalic pattern (ISAHPM) and c) patients with a bleeding pattern resembling that of aneurismatic rupture (ISAHA). This classification could permit the establishment of differences in the management and prognosis.ObjectivesTo describe the clinical and radiological characteristics of these three classes of patients and analyse their medium and long term outcome and moreover, compare these with those observed in patients suffering aneurysmal subarachnoid haemorrhage (ASAH).Material And MethodsA series of 122 patients consecutively admitted to Hospital 12 de Octubre Madrid between 1990 and 2000 with the diagnosis of ISAH were retrospectively reviewed. Patients were considered to have suffered ISAH when the first complete four vessel angiography did not show the presence of any aneurysm or vascular lesion responsible for the bleeding. Patients were classified depending on the pattern of bleeding into ISAHNCT, ISAHPM as described by Van Gijn et al., and ISAHA. The angiography study was repeated when: a) the first study was incomplete or had poor quality, b) vasospasm was present, c) in those patients who had an aneurysmal pattern of bleeding in the initial CT. Different clinical and radiological characteristics were recorded as well as complications that occurred during the hospital stay. Final outcome was evaluated by means of the Glasgow Outcome Score (GOS). With the purpose of comparing these clinical and radiological characteristics and the outcome of patients with ISAH with those suffering aneurysmal subarachnoid haemorrhage (ASAH), 294 patients diagnosed with ASAH during the same study period were also reviewed.Results27% of patients admitted to our hospital with the diagnosis of non-traumatic subarachnoid hemorrhaged were diagnosed as ISAH. Of these, 41% presented with a ISAHA pattern, 39% ISAHPM and 20% ISAHNCT. The average age was similar in the different subgroups of SAH, being around 55 years. There was a greater frequency of male patients in the ISAHNCT and ISAHPM groups. In comparison with ASAH, ISAH characterises by patients presenting with less frequency a bad clinical grade and also loss of consciousness at stroke. There are fewer complications in patients with ISAH than ASAH, with a frequency of rebleeding and ischemia much less (5 and 6% respectively). Within the ISAH group, patients with ISAHA pattern of bleeding present more complications. Outcome is excellent for patients with ISAHNCT and ISAHPM, and rather worse for patients with ISAHA (median followup 5.8 years).ConclusionsThis study confirms that the frequency of ISAH in our environment reaches the higher limit of that shown previously in the literature, replicating the results previously published by our group. Patients with ISAH have a better prognosis and a smaller risk of complications than patients with ASAH, the prognosis of patients with ISAHCTN and ISAHPM being particularly good. Patients with ISAHA present initially with a severe clinical situation, probably related to the bigger amount of bleeding, as well as a higher frequency of systemic complications, cerebral ischemia and hydrocephalus. However, if the absence of vascular lesions is confirmed, the long term prognosis is similar to that of the other subgroups of ISAH.

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