Subarachnoid hemorrhage diagnosed by lumbar puncture after negative computed tomography angiography head

Acute headache is a common emergency department (ED) chief complaint that usually has a benign course. Rare etiologies such as subarachnoid hemorrhage (SAH) can lead to extensive disability or even death. If suspected, SAH requires an intricate and intensive diagnostic investigation. Classic teaching recommends computed tomography head imaging without contrast which, if negative, is followed by lumbar puncture (LP) to rule out SAH. With improvements in computed tomography (CT), practice patterns have begun to adjust to allow computed tomography angiography (CTA) to rule out SAH. This case report describes a 23-year-old woman presenting with headache, neck, and back pain. Her initial CT head and CTA head imaging was negative for SAH. However, 3 days later upon re-presentation to the ED with the same symptoms, an LP was positive for increasing red blood cell count in subsequent tubes. She was transferred to a facility with interventional neurology capabilities where digital subtraction angiography showed a left anterior choroidal saccular aneurysm for which she underwent coiling. Given recent changes in SAH clinical practice guidelines, this case highlights the importance of understanding the current limitations of CT imaging, understanding the risks and benefits of both CT and LP, and always maintaining a high suspicion for especially lethal and disabling conditions such as SAH.