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Objectives: Pial arteriovenous fistulas (pAVFs) are direct connections between the pial artery and vein without an intervening nidus. We report a rare case of craniocervical junction (CCJ) pAVF causing medullary and spinal cord edema resulting from surgical removal of the varix with remnant shunt after coil embolization.Case Description: A 16-year-old man presented with subarachnoid hemorrhage. Digital subtraction angiography revealed a CCJ pAVF with multiple fistulas at the 2 varices (varix A and varix B), which was fed by the bilateral lateral spinal arteries and anterior spinal artery (ASA), and drained into the median posterior vermian vein with varix (varix C) and anterior spinal vein (ASV). Varices A and B were embolized using coils, but the shunts remained in varix C. Then, varix C was surgically removed. After this operation, medullary and spinal cord edema occurred. Digital subtraction angiography showed the ASV drainage responsible for edema. Finally, surgical removal of varices A and B was performed. However, arteriovenous shunts, supplied by the ASA and drained into the ASV via the intrinsic vein, were found in the medulla oblongata and coagulated, resulting in disappearance of edema.Conclusions: Edema was probably caused by concentration of drainage from the arteriovenous shunt in the medulla oblongata into the ASV by surgical removal of varix C acting as another draining route. High flow AVF can induce angiogenesis and secondary arteriovenous shunt. Precise analysis of the angioarchitecture is important to treat such cases without complications. [ABSTRACT FROM AUTHOR]