Background Ruptured and thrombosed cerebral aneurysms pose a risk for rebleeding that may go undetected because they are angiographically occult. The presence of multiple aneurysms may further complicate efforts in accurately identifying the true source because their treatment may circumvent further necessary investigations.

Methods This case series and literature review illustrates the background and clinical features of ruptured thrombosed cerebral aneurysms.

Results Thrombosed ruptured cerebral aneurysms have several common anatomic and physiologic mechanisms for their occurrence. They may evade detection if not considered part of a diligent thorough approach that includes careful analysis of the pattern of initial bleeding on non-contrast head CT scan.

Conclusions Despite negative angiographic studies, and even when multiple cerebral aneurysms are present, diffuse subrachnoid hemorrhage may still warrant further investigation.