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.
10% of these occur in the posterior fossa.In a posterior fossa arachnoid cyst, unlike in DWM:
The cyst is clearly localised in a specific location separate from the fourth ventricle outlets. The cerebellum is not hypoplastic, though it may be compressed by the cyst (mass effect). The CSF flow in the cyst is not continuous with that of the fourth ventricle. Hydrocephalus, if it occurs, is due to the cyst pressing on the cerebellum and compressing the cerebral aqueduct or fourth ventricle outlets. Treatment
The main immediate goal of treatment is the control of hydrocephalus and the enlarged posterior fossa cyst, as these can lead to increased intracranial pressure and brain damage. A minority of those affected do not develop hydrocephalus and are treated based on any associated symptoms or condition. Hydrocephalus/cyst
For hydrocephalus or the posterior fossa cyst, shunts are the mainstay of treatment. However, those with DWM have a higher rate of shunt-related complications than other patients with hydrocephalus (mainly due to the unconventional anatomy). One explanation for a failure of a shunt to reduce intracranial pressure in DWM has been that the cyst may herniate into the foramen magnum and form a scarring adhesion at the cervical junction, preventing it from shrinking again.