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The Chiari II malformation is the most common serious malformation of the posterior fossa, with a frequency of approximately 1 case per 1000 population. Hindbrain dysfunction is the major cause of mortality. The mortality rate is 15% in the first few years of life and is reported to be as high as 50% for the long term rate, regardless of the treatment strategy.zHd影像园
Chiari畸形II型(Chiari II Malformation)MRI病例图片影像诊断分析
【临床病史】：患者，2天的婴儿，胎儿期超声检查发现异常。2-day-old infant noted to have an abnormality on prenatal ultrasound.zHd影像园
Chiari II型畸形是一种复杂的先天畸形，主要有颅骨、硬膜、颅脑、脊椎、脊髓异常表现。被认为是一种原始的神经胚形成病变，几乎都伴有脊膜膨出。同时还有多种伴发的异常，包括小脑扁桃体通过枕骨大孔下疝，小脑半球拉长呈塔状、小脑蚓部超过小脑幕切迹，被盖呈鸟嘴样改变，脑积水、中间块突出，空洞脑、胼胝体发育不良。zHd影像园
【讨论】：The Chiari II malformation is a complex anomaly with skull, dural, brain, spinal and spinal cord manifestations. It is regarded as a disease of primary neurulation and is almost invariably associated with a myelomeningocele. There are multiple associated findings, to include; protrusion of the cerebellar tonsils through the foramen magnum, extension of the cerebellar hemispheres and vermis above the incisura of the tentorium, beaked appearance of thetectum, fenestration of the falx, hydrocephalus, a prominent massa intermedia, colpocephaly, and dysgensis of the corpus callosum.zHd影像园
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【影像诊断】：Chiari II Malformation Chiari畸形II型zHd影像园
【诊断要点】：Chiari II malformations are complex congenital deformities involving the brainstem and cerebellum with a host of associated developmental abnormalities Chiari II型畸形是一种复杂的先天畸形，累及脑干和小脑半球，常有许多伴随的发育异常。zHd影像园
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T2-weighted sagittal (Figure 6 and Figure 7) and axial (Figure 8and Figure 9) images of the spine demonstrate a myelomeningocele at the level of the lower lumbar spine (purple arrows).zHd影像园
There is displacement of the brainstem and lower cerebellum into the cervical spinal canal and a myelomeningocele is almost always present.脑干和小脑下部移位至颈椎管内并且常常会出现脊膜膨出。【影源自图片】MRI图像zHd影像园
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【影像表现】：T1-weighted sagittal images (Figure 1 and Figure 2) and T2-weighted axial images (Figure 3,Figure 4, and Figure 5) of the brain demonstrate a small posterior fossa with herniation of the cerebellar tonsils through the foramen magnum (blue arrows) and a beaked appearance of the tectum (green arrow). There is associated hydrocephalus (red arrow).zHd影像园
Chiari II型畸形是最常见的后颅窝重度畸形，发生率约每1000人群中出现1例。脑后部功能障碍是最主要的死亡原因。在生命最初的几年中死亡率大概是15％，长期来看死亡率达到50％，不管是否采用外科治疗。zHd影像园