Michael P. D'Alessandro, M.D.
Peer Review Status: Internally Peer Reviewed
Is downward displacement of the cerebellum and fourth ventricle into the cervical canal and is part of the meningomyelocele complex.
All types have hydrocephalus that is frequently asymmetric with disproportionate dilation of the occipital horns and atria relative to the frontal and temporal horns. There is a characteristic anterior pointing and medial concavity of the frontal horns, seen on the coronal scans. The massa intermedia is enlarged. The posterior fossa is relatively small. The interhemispheric fissue is sometimes prominent.
Type I - elongation and minimal displacement of the cerebellar tonsils inferiorly.
Type II - marked spinal herniation of the inferior cerebellar vermis, medulla oblongata, lower pons and fourth ventricle. In a newborn Type II is the most common and is nearly always associated with a meningomyelocele.
Type III - displacement of the entire cerebellum into a large cervical spina bifida.
Type IV - isolated cerebellar hypoplasia without significant displacement of posterior fossa contents.
See References Chapter.
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