Differential diagnosis
DWM has a large number of conditions that can present highly similarly on imaging and confound diagnosis. Blakes pouch cyst
Blakes pouch cyst (BPC), or persistent Blakes pouch, is a condition that arises when Blakes pouch, an invagination in the fourth ventricle that ruptures at around 4 months of gestation to form the foramen of Magendie (medial aperture), fails to rupture. This can lead to a dilated fourth ventricle and subsequent hydrocephalus of all four ventricles.In a Blakes pouch cyst, unlike in DWM:
The cerebellum is not hypoplastic, though it may be compressed by the enlarged posterior fossa (mass effect). The posterior fossa is not enlarged. The cerebellar tentorium/confluence of sinuses is not raised. Hydrocephalus, when it occurs, involves all four ventricles.Some authors, however, consider Blakes pouch cyst part of a continuum with DWM (the "Dandy–Walker continuum"). Mega cisterna magna
Mega cisterna magna is a condition in which the cisterna magna, the subarachnoid cistern below the fourth ventricle, is enlarged. It has been proposed to be due to a delayed rupture of Blakes pouch rather than a failed rupture.In mega cisterna magna, unlike in DWM:
The cerebellum is not usually hypoplastic. The fourth ventricle is of relatively normal shape. Hydrocephalus is uncommon.There is debate as to whether this malformation is distinct from DWM or forms part of the "Dandy–Walker continuum". Posterior fossa arachnoid cyst
An arachnoid cyst is a collection of cerebrospinal fluid (CSF) in the arachnoid mater.
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.