女,26岁,因头痛1月入院。头颅CT表现(图1):小脑蚓部、四脑室后见一边界清楚、密度较均匀的类圆形高密度肿块,CT值92~108HU,肿块前缘见点状更高密度影,CT值301HU,四脑室受压前移呈“一”字形,幕上脑室系统对称性扩大,脑实质及颅骨结构未见明显异常。CT诊断:小脑蚓部或四脑室后占 Female, 26 years old, admitted to hospital in January due to headache. Head CT (Figure 1): cerebellar vermis, the fourth ventricle to see a clearly defined, uniform density of round high-density mass, CT value 92 ~ 108HU, see the front edge of the mass higher density, CT value 301HU, the anterior contractile movement of the fourth ventricle was “a” shape, the supratentorial system of symmetry of the ventricle enlarged, no obvious abnormalities in the brain parenchyma and skull structure. CT diagnosis: cerebellar vermis or fourth ventricle accounted for