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Background Distal posterior inferior cerebellar artery (PICA) aneurysms are rare and may present atypically. Subarachnoid hemorrhage (SAH) localized to the posterior fossa can be subtle on initial imaging and may mimic neoplasm or cavernous malformation.Case Description A 72-year-old man with prior lateral medullary infarct presented with acute dizziness and imbalance (NIHSS 0). Initial CT/CTA were interpreted as negative for hemorrhage or large vessel occlusion. MRI demonstrated a hemorrhagic lesion posterior to the fourth ventricle with mild mass effect. Differential included neoplasm, abscess, or vascular lesion. Repeat imaging raised concern for subarachnoid hemorrhage. Digital subtraction angiography (DSA) revealed a distal PICA aneurysm with contribution from a distal AICA pedicle. The aneurysm was treated via primary coil embolization with sacrificeof distal PICA and AICA branches. The patient remained neurologically intact without vasospasm and was discharged home.Conclusion: Distal PICA aneurysms may present with minimal symptoms and NIHSS 0. Posterior fossa SAH may initially mimic mass lesion. Early angiographic evaluation is critical when imaging findings are discordant.Disclosures A. Baryah: None. M. Leary: None. H. Nasser: None. C. Melinosky: None.Abstract E-212 Figure 1