CT-Negative Subarachnoid Hemorrhage in the First Six Hours.

Abstract Background There are no reported cases of negative CT head in the first six hours after a thunderclap headache in a patient found to have an aneurysmal subarachnoid hemorrhage (SAH). Methods We present a case of an anemic patient who experienced aneurysmal SAH with a negative head CT within the first 6 h following thunderclap headache. Results A 47-year-old woman presented with a thunderclap headache and examination showed somnolence and marked meningismus. After a negative CT head was obtained within the first 6 hours of symptom onset, a non-traumatic lumbar puncture (LP) showed consistently bloody collection tubes, prompting repeat imaging that demonstrated a tiny amount of intraventricular hemorrhage. CT angiography revealed an intradural carotid artery aneurysm, and pipeline embolization was successfully performed. Conclusion Non-contrast head CT may be falsely negative within the first 6 hours of aneurysmal SAH in the setting of anemia. In our case, the cause may not have been determined if an LP had not been performed. LP still has a role in diagnosing SAH, particularly in the setting of significant anemia, despite the high sensitivity of non-contrast head CT.