Dandy Walker malformation (DWM), also known as Dandy Walker syndrome, describes a continuum of abnormalities of the posterior fossa (located between the tentorium cerebelli and foramen magnum), that includes complete or partial agenesis of the cerebellar vermis.
The malformations commonly develop during embryonic stages and occur when openings which allow cerebrospinal fluid (a colorless fluid that is found in the brain and spinal cord) to move into the area surrounding the surface of the brain do not open.
The syndrome is also linked with hydrocephalus (“water on the brain”), in which blockage of the normal flow of spinal fluid leads to higher amounts of fluid accumulating in and around the brain.
Moreover, cysts may form in the 4th ventricle, that is a fluid-filled cavity between the cerebellum (a structure which is located at the back of the brain) and brainstem, making the ventricle to enlarge. Ventricles are openings in the brain which produce the cerebrospinal fluid.
Other brain abnormalities of this syndrome include abnormally small gyri or an absence of gyri (a ridge on the cerebral cortex).
DWM is named after doctors Arthur E. Walker and Walter E. Dandy, who described the signs of the syndrome in the early 1900s. After the initial description, more research was conducted which described the numerous morphological characteristics of this syndrome.
In the majority of babies, signs and symptoms of DWM occur during the first 12 months of life, and may include:
- excessive sleepiness;
- jerking movements of the legs and arms;
- problems with vision or hearing;
- abnormal breathing;
- problems with eye movement;
- lack of muscle coordination;
- poor balance and coordination;
- unsteadiness, particularly with walking;
- developmental delays in motor skills, like – walking, sitting up, and talking.
Most affected children have hydrocephalus with an abnormally rapid increase in head circumference. Patients also have a bulging at the back of the skull.
In 10 to 20% of patients with DWM, symptoms do not appear until late childhood or into adulthood. This milder form of DWM, called Dandy-Walker variant, is linked with less severe signs and symptoms.
Associated developmental defects of the central nervous system may include:
- spina bifida (an incomplete closing of the backbone and membranes around the spinal cord);
- dysgenesis of the corpus callosum;
- the Klippel-Feil deformation;
- lipoma of the corpus callosum;
- goloprozenzepalya (occurs as a result of a malfunction in the mechanism of intrauterine growth of the fetus);
- hamartoma in the gray hillock;
- malformation of the lower olivary nucleus;
- dysplasia of the cingulate gyrus;
- malformations of the lobules of the cerebellum;
- the dermoid cyst;
- heterotopy of gray matter;
- microcephaly (the head is smaller than normal);
- occipital encephalocele;
- cerebellar heterotopy.
Doctors still do not completely understand the causes of DWM and its variants. However, potential causes include:
- maternal use of warfarin (a medication which is used to treat blood clots) during pregnancy;
- maternal diabetes;
- exposure of the developing fetus to certain toxins;
- exposure of the unborn baby to viruses, like – Toxoplasma and rubella;
- chromosomal abnormalities associated with the syndrome include triploidy and trisomies (trisomy 18, 13, 21 or 9).
Note – there is 1% chance of recurrence in further pregnancies, but most cases are with no previous family history.
Dandy Walker Syndrome Statistics & Life Expectancy
This syndrome is up to 3 times more common in girls. No racial or ethnic group predominance is observed.
It accounts for about 7.5 percent of the cases of infantile hydrocephalus. The estimated prevalence of a DWS and related variants is about 1 per 30,000 live births.
The syndrome carries a poorer prognosis if diagnosed prior to 21 weeks of gestation. It is estimated that approximately 1 in 5 patients with DWS survives past the first 12 months of life.
An estimated 70 percent mortality is observed in live-born fetuses, commonly due to associated abnormalities. In addition, doctors reported a sudden death in numerous cases, especially due to an inadequate blood supply to the brain.
Seizures occur in about 15% of patients. Also, around fifty percent of patients have normal IQ.
It may be diagnosed in pregnancy by ultrasound as early as 12 weeks after conception. However, ultra-sounds later in pregnancy are more sensitive.
The findings on ultrasound consist of a cyst in the cerebellum. Hydrocephalus is easily visible by ultrasound due to the fact that the lateral ventricles will be markedly dilated.
After birth, tests may include:
- cranial ultrasound – it is done to monitor the development of hydrocephalus;
- MRI and CT scan – they are done to measure the shape and size of the 4th ventricle;
- X-ray of the skull – it is done to check for skull enlargement.
Hydrocephalus associated with DWM is treated with surgery. During the surgery, a tube is inserted to redirect the fluid which surrounds the brain. This tube also helps fluid drainage into other parts of the human body which can absorb the fluid.
In recent years, endoscopic procedures have become more favored than shunt placement in managing obstructive hydrocephalus.
The shunt can be used for the ventricles (ventriculoperitoneal), the cyst, or both. According to the data, the use of drainage procedures and shunt has had an important impact, slashing mortality rates by about 50%.
If the patients struggle with seizures, the healthcare specialist may prescribe medications to help alleviate the symptoms.
For cognitive problems, DWM treatment approaches can include:
- occupational therapy;
- speech therapy.
The effect of DWM on intellectual development is variable, with some children never achieving normal intellectual development even when the excess fluid buildup is treated, whereas other have normal cognition.
Note – if the unborn baby is diagnosed with the syndrome, the expectant mother should be able to attempt a vaginal delivery, unless hydrocephalus develops and leads to an increase in the fetal head which will be too large to pass through the birth canal.
Dandy-Walker Syndrome vs Arnold Chiari Malformation
Chiari malformation is a condition in which brain tissue extends into the spinal canal. Most commonly, it is caused by structural defects in the spinal cord and brain which happen during fetal development.
People with Chiari malformation can have the following symptoms:
- abnormal breathing, like – central sleep apnea;
- neck pain;
- a curvature of the spine (scoliosis);
- spinal cord impairment;
- slow heart rhythm;
- ringing or buzzing in the ears (tinnitus);
- speech problems, like – hoarseness;
- vision problems, like – blurred or double vision;
- difficulty swallowing, occasionally accompanied by choking, gagging, and vomiting;
- numbness and tingling of the feet and hands;
- poor hand coordination (fine motor skills);
- unsteady gait.
Although both are involved in malformation of the posterior fossa structure, these conditions have different mechanisms and causes. In addition, they start at different times in the embryonic development.