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Dandy Walker Syndrome is a neurological disorder that adversely affects brain development, mainly the development of the cerebellum, which is the part of the brain responsible for coordination of movement. In this malformation, various parts of the cerebellum undergo abnormal development, resulting in anatomical abnormalities that can be observed with appropriate neuroimaging. Vermis, the central part of the cerebellum may be very small or absent and may be abnormally positioned. The right and left sides of the cerebellum may be underdeveloped and small as well. In the patients, fourth ventricle (a fluid-filled cavity between the brainstem and the cerebellum) is found to be abnormally large, a condition known as cystic dilatation of the fourth ventricle. Posterior fossa, the part of the skull that contains the cerebellum and the brainstem is also abnormally large in size. These cerebellar abnormalities offer various types of limitations and difficulties with movement, coordination, intellect, and other neurological functions. Dandy-Walker Syndrome is estimated to affect approximately 1 in 10,000 to 30,000 newborns. It accounts for about 7.5% of the cases of infantile hydrocephalus. Dandy Walker Syndrome is known as the most common posterior fossa malformation.
Dandy Walker Syndrome represents several abnormalities of brain development which coexist. Three different identified types of Dandy Walker complexes closely represent associated forms of the Syndrome: Dandy Walker Syndrome malformation, Dandy Walker Syndrome mega cisterna magna & Dandy Walker Syndrome variant. The Dandy Walker Syndrome malformation is the most severe presentation with complete agenesis of the cerebellar vermis. This involves hydrocephalus, cystic dilation of the fourth ventricle, and complications due to coexisting genetic conditions, such as Spina Bifida. Variant form is less severe than the malformation type. This form is associated with the most wide-ranging set of features and outcomes of Dandy Walker Syndrome. Hydrocephalus is seen in 25% of cases & the third and lateral ventricles as well as the brain stem are normal.
About 70% mortality is observed in live-born fetuses, often due to associated abnormalities. The syndrome carries a poorer prognosis if diagnosed prior to 21 weeks of gestation and better prognosis if diagnosis is made postnatally.
Genetic mutations thought to cause Dandy-Walker Syndrome have been found, but these mutations account for a very small number of actual clinical cases. Many types of chromosomal abnormalities are also associated with Dandy-Walker Syndrome. The syndrome can be associated with condition in which there is an extra copy of one chromosome in each cell (trisomy). Dandy-Walker Syndrome most often occurs in people with an extra copy of chromosome 18 (trisomy 18), but can also occur in people with trisomy 13, trisomy 21, or trisomy 9. The syndrome can also be associated with deletions or duplications of particular pieces of certain chromosomes. It can also be a feature of various different genetic syndromes that are caused by specific genetic mutations.
Dandy-Walker Syndrome could be caused by environmental factors that affect embryological development (early development before birth). Fetal exposure to substances that cause birth defects (teratogens) may play a significant role in causing this condition. A diabetic mother is more likely than a non-diabetic mother to bear a child with Dandy-Walker Syndrome. Most cases are sporadic, which means they occur in people with no family history of the disorder. A small subset of cases seems to run in families; however, a clear pattern of inheritance is not found.
Dandy Walker syndrome is also considered as part of an emerging class of diseases called ciliopathies. The underlying cause may be a dysfunctional molecular mechanism in the primary cilia structures of the cell, leading to defects in numerous critical developmental signalling pathways, vital to cellular development. Dandy Walker Syndrome is also found to often occur in patients with PHACES syndrome (Posterior fossa malformations-hemangiomas-arterial anomalies-cardiac defects-eye abnormalities-sternal cleft and supraumbilical raphe syndrome).
Signs and symptoms:
In a vast majority of patients with Dandy-Walker malformation, clinical features are present at birth or develop during the infancy period. Some children suffer with hydrocephalus (buildup of fluid in the brain) that may lead to disproportionate increase in the head size (macrocephaly). About 50% of affected individuals have mild to severe intellectual disability, and those with normal intelligence may suffer with learning disabilities of various grades. Children with Dandy-Walker malformation often suffer with global developmental delay, particularly delay in motor skills such as crawling, walking, climbing, and coordinating movements of the upper and lower limbs.
Signs and symptoms often include muscle stiffness, spastic paraplegia (paralysis of the lower limbs), vision problems, hearing abnormalities, and seizures. Many other types of brain abnormalities have been reported, albeit less commonly. These abnormalities include agenesis of corpus callosum (absent or underdeveloped tissue that connects the left and right halves of the brain), occipital encephalocele (sac-like protrusion of the brain through an opening at the back portion of the skull), or failure of some neurons (nerve cells) to migrate to their standard location in the brain during embryonic development. When these additional brain malformations are present, more severe signs and symptoms are experienced by the patients.
Dandy-Walker malformation not just affects the brain, but abnormalities in other systems can also be seen. Such abnormalities may include heart defects, urogenital tract malformations, polydactyly (presence of extra fingers or toes), syndactyly (fused fingers or toes), or abnormal craniofacial features. In about 10-20% of the patients, typical signs and symptoms do not appear until late childhood or into adulthood. These individuals in whom the clinical features manifest late, usually a different range of features is observed than those affected in infancy, including unsteadiness of gait, headaches, facial palsy (paralysis of facial muscles), hypertonia (increased muscle tone), muscle spasms, mental abnormalities and behavioral changes. In rare cases, patients may have no observable signs or symptoms.
Most common cause of death in Dandy Walker Syndrome is attributed to problems related to hydrocephalus or complications of its treatment.
Dandy Walker Syndrome is diagnosed by neuroimaging that includes CT & MRI of brain. To ascertain the underlying cause, genetic tests should be done. Antenatal sonography can detect the syndrome by marked enlargement of the cisterna magna, complete aplasia of the vermis & gap between the cerebellar hemispheres. Although if ultrasound scanning is performed before 18 weeks of gestation, false diagnosis is not uncommon due to improper formation of vermis by that time. In general, MRI brain is the investigation modality of choice for assessment of Dandy Walker Syndrome. CSF flow study is also recommended to the associated hydrodynamic changes.
In asymptomatic cases, though found to be very rare, no treatment is required. Hydrocephalus associated with Dandy Walker syndrome is treated ventriculoperitoneal shunting in which a tube is inserted to redirect the fluid around the brain and to drainage of this fluid into the peritoneal cavity. Physical and vocational therapy is needed to manage the functional limitations arising out of muscle hypertonia, stiffness, gait abnormalities and coordination problems. Behavioral, educational and psychological therapies are required for the children to attain best outcomes.
Other names of the condition:
Mega cisterna magna
Dandy Walker syndrome
Dandy Walker malformation
Dandy Walker complex