This is usually inserted in the posterior fossa, but a shunt in the lateral ventricles may be used instead or in conjunction. Endoscopic third ventriculostomy (ETV) is a less invasive option for patients older than 1 year. Posterior fossa shunts are most effective (80% of the time) but carry the highest risk of complications, while ETV is least effective but has the least risk of complications. The mortality rate is roughly 15%, mostly due to complications from hydrocephalus or its treatment, which can include subdural haematomas or infection. The prognosis after successful hydrocephalus treatment is usually good but depends on any associated condition and its symptoms. Those without hydrocephalus are treated based on any associated symptoms or condition.The prevalence of DWM is estimated at between 1 in 25,000 to 1 in 50,000. DWM is the cause of around 4.3% of cases of congenital hydrocephalus and 2.5% of all cases of hydrocephalus. At least 21% of those with DWM have a sibling with the malformation, and at least 16% have a parent with the malformation. The malformation was first described by English surgeon John Bland-Sutton in 1887, though it was named by German psychiatrist Clemens Ernst Benda in 1954 after American neurosurgeons Walter Dandy and Arthur Earl Walker, who described it in 1914 and 1942, respectively. Signs and symptoms
Hydrocephalus
The most frequent and prominent symptoms of DWM are those associated with hydrocephalus in the postnatal period. Hydrocephalus occurs in an estimated 80% of patients with classic DWM.
The melanocytic tumours in these cases are thought to relate to the same genetic errors in the development of the embryonic neural tube that lead to the DWM, since the subsequent embryonic neural crest gives rise to melanocytes, among other cells. 10% of patients had endocrine or metabolic disorders, and 2.7% had excessive hair growth (hypertrichosis). 9% of patients (almost all with classic DWM) had musculoskeletal abnormalities, which included scoliosis or kyphoscoliosis and arthrogryposis. 5.9% of patients had underdeveloped reproductive organs, such as hypoplastic genitalia or undescended testicles (cryptorchidism). 5.3% of patients had underdeveloped or polycystic kidneys.Occipital encephalocele may occur in DWM. This has generally been found at rates between 6 and 8%. It has been suggested to occur to compensate for the increased pressure in the posterior fossa during foetal life.Syringomyelia occasionally occurs with DWM, though it is not certain how often. One review reported an occurrence of 4.3% in a sample. This may be due to herniation of the bottom of the cyst through the foramen magnum (a similar mechanism to Chiari malformation). Alternatively, it may be a result of hydrocephalus, in which it forms as a "fifth ventricle" due to an enlarged central canal.Rarely, spina bifida has been found with DWM. When it is present, it is usually spina bifida occulta. Cause
DWM is caused by any disruption to embryonic development that affects the formation of the cerebellar vermis. This is usually a genetic mutation that results in impaired cell migration and division. A large number of genetic conditions can result in the anomaly.