Delayed MRI following angiogram-negative subarachnoid hemorrhage was low yield and is not routinely necessary, according to a study published in the April issue of Clinical Radiology.

MRI has been posited as a potentially helpful imaging tool in patients with non-perimesencephalic angiogram-negative spontaneous subarachnoid hemorrhage (AN-SAH). Though patients at the institution of senior author J. Byrne, MD, of the John Radcliffe Hospital in Oxford, England, were undergoing delayed MRI eight weeks after the ictus, the usefulness of this strategy was unknown. Woodfield and colleagues assessed the diagnostic yield of delayed MRI in identifying a cause of AN-SAH in their study.

The study reviewed all patients presenting with spontaneous subarachnoid hemorrhage who had negative CT angiography and catheter angiography over a six year period. During this time, 1,023 angiograms were performed for a new presentation of subarachnoid hemorrhage. Two hundred forty-two, or 23.7 percent, did not show cause for the hemorrhage. Another catheter angiogram was performed in 48 patients and aneurysms were found in two patients.

Out of the remaining 240 patients, 131 underwent a subsequent MRI brain scan. One hundred and five, or 80.2 percent, of MRI exams were performed four or more weeks after angiography. Cavernomas were discovered to be the likely bleeding source in two of the patients. Thirty-nine patients underwent cervical spine MRI and none were identified as the cause. None of the patients re-presented to the institution over the study period.

“MRI may be useful in confirming the diagnosis of cavernoma where this is suspected from the presentation CT, but is unlikely to identify an occult cause of AN-SAH in patients where the initial imaging or clinical presentation is not suggestive of an underlying angiographically occult vascular lesion,” wrote Byrne and colleagues. “In patients with signs or symptoms suggestive of spinal vascular anomalies, MRI of the whole spine may provide useful diagnostic information.”