Glossary of Diagnoses and Terminology

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Dandy-Walker malformation and variants

Dandy-Walker malformation and variants refer to a nonspecific congenital brain malformation characterized by (1) the incomplete or underdevelopment of the cerebellar vermis, the middle portion of the cerebellum, the part of the brain located at the back of the skull, (2) cystic enlargement of the 4th ventricle, and (3) an enlargement of the small space located near the brainstem and cerebellum called the posterior fossa. Dandy-Walker malformation and variants have an approximate incidence rate of 1 in 5,000 livebirths.

A diagnosis of Dandy-Walker is most accurate when made after 18 weeks of gestation; however, severe malformations can be detected earlier in pregnancy. An early diagnosis and the presence of additional anomalies are associated with a poorer prognosis. Dandy-Walker has a high perinatal mortality rate, ranging from 30-70%.

Dandy-Walker malformation and variants can be the result of single gene disorders, chromosomal abnormalities, or environmental factors. It can occur as an isolated malformation or in conjunction with other anomalies. Following a diagnosis of Dandy-Walker, further testing such as computerized tomography (CT) scan, magnetic resonance imaging (MRI), and fetal karyotype should be conducted to determine if other anomalies are present.

Dandy-Walker is associated with agenesis of the corpus callosum, atrial septal defect, cleft lip and cleft palate, congenital heart defects, hydrocephalus, neural tube defects, ventricular septal defect, chromosomal abnormalities such as triploidy, trisomy 13, and trisomy 18, and malformations of the gastrointestinal, genitourinary, and skeletal systems.

The recurrence risk depends on whether the condition is isolated or associated with additional anomalies. When associated with chromosomal abnormalities, the recurrence risk is the maternal-age related risk for aneuploidy. If the condition is associated with other structural malformations, such as cleft lip and cleft palate or congenital heart defects, there is an additional recurrence risk of 5%. If the Dandy-Walker malformation is an isolated diagnosis, the recurrence risk ranges from 1% and 5%. [23]