It can be diagnosed prenatally on ultrasound as early as 14 weeks of gestation, although it is usually diagnosed postnatally by MRI. It is diagnosed within the first year of life 41% of the time, normally due to increasing signs of hydrocephalus, but 28% of the time it is discovered in adolescence or adulthood due to mental health problems, such as psychosis or mood disorder. Criteria and classification
The precise diagnostic criteria and classification systems of DWM are not agreed upon, and significant dispute exists as to which terms or criteria should be used. The core criteria of DWM are hypoplasia of the cerebellar vermis and an enlarged fourth ventricle and posterior fossa (the space behind the cerebellum), though the specific degree of hypoplasia or cystic enlargement for diagnosis of DWM is not agreed upon. Additionally, there are several similar conditions which have at various times been grouped with DWM on a continuum by some authors and separated as distinct by others, further complicating diagnosis.In 1976, Harwood-Nash and Fitz proposed the term Dandy–Walker variant (DWV) for a malformation in which the posterior fossa is not enlarged but the cerebellar vermis is hypoplastic. In 1989, Barkovich et al. proposed the term Dandy–Walker complex (DWC) to include classic DWM and DWV (under type A) plus a third malformation (under type B) in which the cerebellar vermis remains large enough to sit between the fourth ventricle and the cisterna magna beneath it, and instead it is mostly the cisterna magna that is enlarged.
Complications from overdrainage such as subdural haematomas are also possible and can lead to mortality. Shunts in the fourth ventricle (cystoperitoneal shunts, or CP shunts) have a generally high rate of successful cyst and ventricle size reduction, especially in the cyst (at least 80%). With a shunt in the lateral ventricles (ventriculoperitoneal shunt, or VP shunt), studies have generally found a roughly 50% successful cyst size reduction rate, with successful ventricle size reduction roughly two thirds of the time.Other systemic or genetic conditions are often present with DWM, and each have their own significant effect on prognosis. Epidemiology
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.A 2017 review found that most patients (65%) were diagnosed with either "Dandy–Walker malformation" or "Dandy–Walker syndrome", while 20% were diagnosed with "Dandy–Walker variant" and 1.1% with "mega cisterna magna". History
The malformation was first described in 1887 by English surgeon John Bland-Sutton as hypoplasia of the cerebellar vermis, an enlarged posterior fossa and hydrocephalus. In 1914, American neurosurgeon Walter Dandy and American paediatrician Kenneth Blackfan described the malformation as partial or complete absence of the cerebellar vermis, an enlarged fourth ventricle and hydrocephalus.