RESUMEN
OBJECTIVE: Our goal was to assess the value of MR imaging to patient care in the setting of angiographically negative subarachnoid hemorrhage and to evaluate the potential of MR imaging for revealing the mechanism for idiopathic perimesencephalic subarachnoid hemorrhage. MATERIALS AND METHODS: We retrospectively reviewed 71 patients who presented with subarachnoid hemorrhage and in whom the results of a four-vessel cerebral arteriogram were negative, a CT scan showed no evidence of intraaxial hemorrhage, and MR imaging had been performed within 72 hr of presentation. MR imaging of the brain included sagittal spin-echo T1-weighted, turbo spin-echo proton density-weighted, T2-weighted, and axial T2-weighted gradient-echo sequences. MR imaging of the cervical spine, which was performed in 41 of the 71 patients, included sagittal spin-echo T1-weighted, turbo spin-echo proton density-weighted, T2-weighted, and axial T2-weighted gradient-echo sequences. RESULTS: Perimesencephalic subarachnoid hemorrhage was seen on CT in 25 patients; in four of these patients (16%), MR imaging revealed acute perforator territory infarction involving the caudate, putamen, or thalamus. In 26 other patients, nonperimesencephalic subarachnoid hemorrhage was revealed on CT; in two of these patients (8%), MR imaging showed the cause of the subarachnoid hemorrhage. By contrast, 20 patients had negative findings on CT scans but xanthochromic CSF on lumbar puncture; in two of these patients (10%), MR findings were interpreted as responsible for subarachnoid hemorrhage. CONCLUSION: MR imaging showed diagnostic value in patients with angiographically negative subarachnoid hemorrhage, revealing abnormalities in 14% of the 71 patients, and resulted in a significant change in patient treatment in 6% of the patients. MR imaging also revealed an association between perimesencephalic subarachnoid hemorrhage and infarcts involving the territory of perforating arteries at the base of the brain. This finding may provide insight into the pathogenesis of perimesencephalic subarachnoid hemorrhage.