page_title: Dandy–Walker malformation
section_title: Pathophysiology
hierarchical_section_title: Dandy–Walker malformation / Pathophysiology
context_page_description: Dandy–Walker malformation, also known as Dandy–Walker syndrome, is a rare congenital brain malformation in which the part joining the two hemispheres of the cerebellum does not fully form, and the fourth ventricle and space behind the cerebellum are enlarged with cerebrospinal fluid. Most of those affected develop hydrocephalus within the first year of life, which can present as increasing head size, vomiting, excessive sleepiness, irritability, downward deviation of the eyes and seizures. Other, less common symptoms are generally associated with comorbid genetic conditions and can include congenital heart defects, eye abnormalities, intellectual disability, congenital tumours, other brain defects such as agenesis of the corpus callosum, skeletal abnormalities, an occipital encephalocele or underdeveloped genitalia or kidneys. It is sometimes discovered in adolescents or adults due to mental health problems.
  DWM is usually caused by a ciliopathic or chromosomal genetic condition, though the causative condition is only identified in around half of those diagnosed before birth and a third of those diagnosed after birth.
context_section_description: The cerebellum begins forming at the fifth week of embryonic development. It differentiates at the top of the metencephalon, while the pons (in the brainstem) differentiates at the bottom, separated by the fourth ventricle. The cerebellar hemispheres form from the rhombic lips on the forward surface of the fourth ventricle, which expand and roll over to fuse in the midline to form the cerebellar vermis by the 15th week. If this process does not complete, the cerebellar vermis will not form fully. This long period of development of the cerebellar vermis makes it particularly vulnerable to disruptions.
  In DWM, the fourth ventricle opens up into and is continuous with almost the entire posterior fossa subarachnoid space.
caption: Diagram of the cerebellum, fourth ventricle and pons. The white arrow shows the foramen of Magendie (medial aperture) connecting the fourth ventricle to the cisterna magna (3). This usually remains open in DWM.[6]