Background: A cerebral CT scan is routinely performed in all patients evaluated for subarachnoidal haemorrhage. Quick and accurate diagnosis is of the utmost importance in such patients, but the accuracy and value of the initial CT scan has not been fully established.
Material and methods: Initial CT scans of 70 patients (45 women) with subarachnoid haemorrhage were reviewed retrospectively. Cerebral CT scans were performed without intravenous contrast and evaluated independently by two observers.
Results: CT scans were positive for blood in the cerebrospinal fluid spaces in 64 out of 70 patients (91%). Blood was most frequently seen in basal cisterns (75%), Sylvian Fissure (73%) and cerebral cortical sulci (67%). Evidence of raised intracranial pressure was present in 26 patients (41%). The site of the ruptured aneurysm could be localised by CT with high accuracy only in ruptured aneurysms of the middle cerebral artery. The median time from symptom onset to examination was significantly higher in patients with a normal than a pathological CT scan (87 hours vs. 4 hours, p < 0.001). A lumbar puncture was positive for blood in all six patients with a normal CT scan.
Interpretation: This study demonstrates that a lumbal puncture should be performed after a normal cerebral CT scan if subarachnoid haemorrhage is clinically suspected.