Pediatric aneurysms are rare and pediatric subarachnoid hemorrhage due to aneurysm are even rarer. Pediatric aneurysms and their adult counterparts differ in demographics, location, and type. Pediatric patients have a greater tendency to have giant and dissecting aneurysms, which thrombose spontaneously. Case description: A 15-year-old boy who had mild headache and fever for three months presented to a local hospital with severe headache, vomiting, a generalized seizure and consciousness

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... ance. Imaging examination showed intracranial hemorrhage of unknown bleeding source spreading with subarachnoid hemorrhage and intraventricular hemorrhage. He was transferred to our hospital for close treatment. In our hospital's Computed Tomography Angiography, swelling of the arterial wall was found on the left side of the A1A2 junction. The left fronto-temporal craniotomy was performed with the external ventricular drainage. After the parent artery was secured, the entire circumference of the aneurysm was exposed. The aneurysm was a thrombosed giant fusiform aneurysm and continuous with the thrombosed left A1 segment. The aneurysm was trapped by total three clips. Postoperatively, he had not occurred vasospasm, and transferred rehabilitation hospital with mild motor aphasia. Conclusion: Pediatric aneurysms are rare, and often present as dissecting thrombosed aneurysms or giant aneurysms. ACA dissecting aneurysms are rare but often occur at a young age, and they easily cause thrombosis, which may occlude the aneurysm and the parent artery, resulting in unknown bleeding sources. It is necessary to suspect rupture of an ACA dissecting aneurysm if there is an ICH and SAH of an unknown source of bleeding where the hematoma is localized near the ACA. Craniotomy can effectively remove the hematoma and identify the bleeding source, and it is more desirable to secure the parent artery to prevent rerupture.