Imaging Strategy for Patients With Aneurysmal Subarachnoid Hemorrhage and Negative Initial Imaging: Evidence,...

Subarachnoid hemorrhage (SAH) is frequently caused by a ruptured saccular cerebral aneurysm, making early and accurate diagnosis critical for patient outcomes. CT angiography (CTA) is the standard first-line imaging modality for suspected nontraumatic SAH; however, up to 15% of patients present with negative initial CTA findings, necessitating further imaging work-up. A key distinction in SAH is between an aneurysmal and a non-aneurysmal bleeding pattern. Perimesencephalic hemorrhage, a distinct SAH subtype, exhibits a contained bleeding pattern rarely associated with an underlying aneurysm, and therefore requires a different imaging approach than aneurysmal SAH. Given the alarmingly high mortality of untreated ruptured cerebral aneurysms, a comprehensive imaging strategy enabling prompt identification of intracranial aneurysms is essential to prevent rebleeding. This narrative expert review discusses the available evidence for the optimal imaging strategy in patients presenting with aneurysmal-pattern SAH and initially negative findings. It addresses potential pitfalls in neurovascular imaging, offers guidance on identifying rare causes of SAH through advanced imaging techniques, and examines the yield of repeat neuroimaging in the context of evolving imaging technologies. Finally, we address the diagnostic challenges posed by rarer aneurysm subtypes, including spinal artery aneurysms, dissecting aneurysms, blood blister-like aneurysms, and perforating artery aneurysms. Together, these insights inform the development of a comprehensive, patient-centered imaging algorithm for improved care in cases of aneurysmal SAH without a detectable aneurysm on initial imaging.