患者,男,40岁。枕部肿物数年,近2年来,枕部肿物增大,压之易退。体检　后枕部可触及拇指头大小肿物,呈囊性感,压之消退。Ｘ线平片　头颅侧位片示枕骨有大片无骨结构之透亮区,与乳突气房连成一片,枕骨内、外板变薄。汤氏位片示枕骨后下部见大片透亮区,与左侧乳突气房相连成片,且 Patient, male, 40 years old. Occipital tumor for several years, nearly 2 years, the occipital tumor increases, the pressure of easy to retreat. Physical examination can be reached after the occipital thumb size tumor, was cystic sexy, pressure subsided. X-ray plain skull showed a large occipital bone-free structure of the translucent area, and mastoid air room even into a piece of the occipital bone, the outer thinning. Thompson piece shows the lower part of the occipital bone see large translucent area, connected with the left mastoid air chamber into pieces, and