Detection of a ruptured aneurysmal sac by MRI in a case of negative angiogram. Successful clipping of an anterior communicating artery aneurysm. Case report.

A case of a ruptured aneurysm is presented in which the angiograms did not disclose the sac. Rupture of an aneurysm of the anterior communicating artery was suspected from the distribution of subarachnoid blood on computerized tomography (CT), and the presence of a sac was highly suggestive on magnetic resonance imaging (MRI), which led us to open surgery. A non-thrombosed aneurysm was discovered at the suspected site, and successfully clipped. The necessity is discussed of MRI investigation in patients with subarachnoid haemorrhage (SAH) of unknown aetiology.