Perimesencephalic subarachnoid hemorrhage: when to stop imaging?

To evaluate the yield of digital subtraction angiography (DSA) and repeated follow-up imaging in patients with initial pattern of perimesencephalic subarachnoid hemorrhage (PSAH) and negative computed tomography angiography (CTA) in excluding an underlying aneurysm. We conducted a retrospective analysis of all nontraumatic SAH who underwent a DSA between January 2006 and January 2010 and selected those with a PSAH pattern on CT done within 72 h from ictus. All CTAs were performed with a 64-section multidetector row CT scanner, and findings were compared with DSA and to follow-up imaging. Forty-nine patients with initial PSAH pattern and negative CTA who underwent subsequent DSA were identified. Six patients were excluded because CTA was not available in hospitals or 72 h after ictus. Only one patient (2.4%) had a false negative CTA with a 1-mm left ICA aneurysm seen on DSA, considered not to be the source of hemorrhage. An average of 2.0 ± 1.2 follow-up exams per patient (range 0-5) revealed no source of bleeding. One patient had a procedure-related transient complication, but evolved with no sequels. In patients with PSAH, CTA is reliable for ruling out an underlying aneurysm. DSA and, especially, further follow-up imaging have no increased diagnostic yield compared to initial negative CTA.