Chromosomal abnormalities
In those who are diagnosed with DWM before birth on ultrasound, up to half are found to have a chromosomal abnormality, with the most common being Edwards syndrome (trisomy 18), at roughly 26% of prenatal DWM cases. 6.5% of those diagnosed with DWM after birth also have Edwards syndrome. Other chromosomal abnormalities that can lead to DWM include triploidy, Patau syndrome (trisomy 13), trisomy 9 and partial 3q deletion or duplication. The 3q24 region contains the ZIC1 and ZIC4 genes, known to be associated with DWM. External toxins
Warfarin use during pregnancy has been known to lead to systemic defects in the fetus, including ocular dysgenesis, microcephaly, agenesis of the corpus callosum, skeletal abnormalities and heart defects. In 1985, it was also linked to DWM. Pathophysiology
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. Pathophysiology of hydrocephalus
The reason why hydrocephalus occurs in DWM is not yet fully understood.
A compressed brainstem is not a contraindication, however. ETV has a more modest success rate than shunts, as the hole often closes over. It is more likely to fail in younger patients (below 1 year), and its effects on the developing brain are not yet known. Cysts posterior to the cerebellum, presenting in children younger than 5 years, have been labeled developmental retrocerebellar cysts under a new classification in relation to the proposed neuroendoscopic management.Previously, craniotomy of the posterior fossa and excision of the cystic membrane was used, which was often unsuccessful in preventing cyst reformation and carried a degree of mortality. This may still be reserved for patients with repeated shunt failures/infections. Other
Treatments for any other symptoms are generally focussed on the specific condition involved and may include supported education, physical therapy or other services. Genetic counselling may be offered to parents for future conceptions. Prognosis
The prognosis is first and foremost dependent on the early and successful treatment of hydrocephalus, if present. The other significant factor affecting prognosis is the presence of a comorbid genetic condition or brain anomaly.Mortality rates from DWM are roughly 15%. In a study of Dandy–Walker variant (DWV), a mortality rate of 12.5% was observed. The most common cause of death is complications from hydrocephalus or its treatment. Untreated hydrocephalus can lead to increased intracranial pressure and brain damage. Shunts used to treat DWM have a moderate-to-good success rate, but they have a higher-than-average failure rate, which can result in failure to reduce the intracranial pressure or infection, such as meningitis.