Fig. 1

a MRA showed a poor arterial supply (yellow arrow). The artery closest to the lesion is located outside the lesion (red arrow). b CT suggested an irregular destruction of the occipital bone and small cysts within the lesion. c MRV showed the left transverse sinus was blocked totally (yellow arrow). d The postoperative CT was negative, no obvious sign of bleeding. e Pathological examination found “giant cells” around the cysts (green arrow), which should be hemosiderin-laden macrophages. We can see that these cells are scattered within the lesions (yellow arrow). f There were numerous cystic spaces (blue arrow) containing bloody fluid (red arrow) in the lesion, which is easily mistaken as an ABC