Dandy-Walker complex is a group of disorders that affect the development of the brain. The changes in brain development are present from birth (congenital). Dandy-Walker complex affects the formation of the area of the brain known as the cerebellum, which is responsible for coordinating movement, and the fluid-filled spaces around it. People with Dandy-Walker complex may have a portion of the brain called the cerebellar vermis that is smaller than expected (hypoplastic) or completely absent (aplastic). The cerebellar vermis is the area of the brain between the two halves of the cerebellum. People with Dandy-Walker complex have a larger than expected fourth ventricle of the brain. This ventricle allows fluid to flow between the upper and lower areas of the brain and spinal cord. People with Dandy-Walker complex may have an enlarged portion of the base of the skull (posterior fossa). Dandy-Walker complex may be more common in females than in males. Dandy-Walker complex is a group of disorders that have overlapping symptoms. These disorders include: Dandy-Walker malformation (also known as Dandy-Walker syndrome): having a small cerebellar vermis, large fourth ventricle, and enlarged posterior fossa Isolated cerebellar vermis hypoplasia (sometimes known as Dandy-Walker variant): having a small cerebellar vermis without other features of Dandy-Walker complex Mega-cisterna magna: having an enlarged posterior fossa with a typically developed cerebellum. This may be a normal variant and may not cause any health problems. In some cases, Dandy-Walker complex is caused by an underlying genetic change. These genetic changes may cause Dandy-Walker complex alone, or they may cause Dandy-Walker complex as well as other health problems. In these situations, the complex can run in families. However, in most situations, Dandy-Walker complex is caused by a combination of genetic and environmental factors. Dandy-Walker complex can be diagnosed by imaging of the brain such as ultrasound, CT scan, or MRI scan.