The syndromes of vermal agenesis are reviewed from the Department of Pediatrics, Hopital des Enfants Malades, Paris, France. These include the Dandy-Walker syndrome and other complicated cases associated with multiple abnormalities. The Dandy-Walker syndrome consists of three abnormalities of development: 1) Partial or complete agenesis of the vermis of the cerebellum; 2) cystic formation in the posterior fossa communicating with the fourth ventricle; and 3) hydrocephalus. Enlargement of the posterior fossa and elevation of the torcular and lateral sinuses are sometimes included among the diagnostic criteria. Associated abnormalities include agenesis of the corpus callosum (7-15% of patients), occipital encephalocele (18%), cleft lip and palate, cardiac malformations, urinary tract abnormalities, and minor facial dysmorphisms. The prognosis is guarded, 75% having borderline IQ or lower, and a mortality rate of 27% in some series. Various chromosomal abnormalities have been demonstrated in a few patients but their significance is unclear. There is a 1-2% chance of recurrence in the same family. Syndromes of agenesis of the cerebellar vermis of genetic origin are distinguished from the Dandy-Walker malformation. These include Joubert syndrome, Walker-Warburg syndrome, Meckel-Gruber syndrome, and atypical Dandy-Walker with facial angioma. Joubert syndrome includes panting respirations, abnormal eye movements, facial asymmetry and ataxia, in addition to vermian agenesis. The MRI shows an umbrella shaped fourth ventricle. Walker-Warburg syndrome includes lissencephaly, retinal abnormalities and hydrocephalus. Meckel-Gruber syndrome is characterized by occipital encephalocele, polycystic kidneys, Polydactyly and hydrocephalus. Some have congenital muscular dystrophy in addition. The inheritance pattern is autosomal recessive. An MRI with median sagittal cuts is usually required in the diagnosis of partial agenesis. No reliable metabolic marker has been determined but some cases of vermian agenesis are associated with abnormal urinary excretion of succinyl-purines and pipecolic acid. Shunting operations are required when hydrocephalus develops. Operations on the posterior fossa have a high rate of failure. Prognosis depends on the occurrence of other CNS abnormalities. 
COMMENT. In patients with agenesis of the cerebellar vermis a correct diagnosis is important in therapy, genetic counseling, and prognosis. Cases with complications which are usually autosomal recessive in inheritance and having a poor prognosis must be distinguished from the typical Dandy-Walker syndrome which is often amenable to surgical therapy.