Background. Aneurysms of the distal anterior cerebral artery (DACA) are uncommon; they often form near the pericallosal-callosomarginal junction and are typically small. To our knowledge, giant DACA aneurysms developing from the more distant parts of the anterior cerebral artery (ACA), A4-5, have been described only once in the literature. Case description. A 66-year-old gentleman reported with a brief loss of consciousness followed by weakness in his right lower leg. The patient was admitted with a Glasgow Coma Score (GCS) of 15. A computed tomography (CT) scan of the head revealed a left hyperdense mass in the frontal parasagittal supracallosal region. Contrast MRI revealed a heterogeneously enhancing mass measuring 35x30x25 mm. CT angiography (CTA) revealed a small saccular aneurysm on the posteromedial aspect of the mass, perpendicular to the vertical plane of the coronal suture, corresponding to the A4-A5 junction of the left ACA. Through a left paramedian craniotomy, a modified anterior interhemispheric approach that was more posterior than the conventional projection was performed. A giant partially thrombosed was found. The aneurysm was resected, and the neck was reconstructed using four clips placed on top of them to enhance the clipping force over any remaining thrombus. The patient recovered as expected and was neurologically intact three months later. Conclusion. Giant distal anterior cerebral artery (DACA) aneurysms found in the A4-A5 segment represent a pathologically uncommon phenomenon. Due to the rarity of giant aneurysms at this location, their reporting is important to inform meticulous pre-operative planning.
