Ultrasound
Findings: Classic abnormal findings described on cranial CT and MRI scans also can be demonstrated on cranial sonography. Commercially available equipment is used with a 3- to 7.5-MHz transducer, depending on the size of the patient's head. Transducers of 5- to 7.5-MHz are used for newborns, and transducers of 3- to 5-MHz are used for older infants.
On US, a large posterior fossa midline cyst, which communicates with the fourth ventricle, is demonstrated best on midline sagittal sections. The anterolaterally displaced hypoplastic cerebellar hemispheres are seen best in the coronal projection. Sagittal and coronal sections can demonstrate the enlargement of the posterior fossa, high position of the tentorium, and dilated third and lateral ventricles.
Scans performed with the transducer not only by using the transfontanel approach but also by placing it directly over the posterior or posterolateral fontanelle can show a large posterior fossa cyst and hypoplastic cerebellar hemispheres.
It is important in these patients to assess the supratentorial compartment for associated anomalies, such as callosal agenesis.
Using US, Dandy-Walker malformation usually is discovered before birth although prominence of the cisterna magna is often confused with Dandy-Walker malformation in utero (see Image below).
Caption: Dandy-Walker malformation. In utero sonogram of Dandy-Walker malformation. Note abnormal cerebellar vermis in association with a posterior fossa cyst (arrow) and splaying of the cerebellar hemispheres. Image courtesy of Ecker et al.Prenatal diagnosis of Dandy-Walker malformation should not be made before the 18th week of gestation because development of the cerebellar vermis may be incomplete at that time. Although great variability exists in intracranial findings in fetuses, sagittal measurements exceeding 10 mm help confirm the presence of a Dandy-Walker cyst. US examination, including fetal echocardiography, should be directed toward identifying additional supratentorial and extracranial anomalies. Follow-up sonograms are useful for monitoring cyst size and ventriculomegaly. Three-dimensional US reportedly proved most helpful in delineating the exact nature and anatomic level of the anomaly in utero.
Degree of Confidence: US is heavily operator dependent. Associated findings of Dandy-Walker malformation may be missed, such as pachygyria, polymicrogyria, heterotopias, and dural abnormalities.
False Positives/Negatives: Fetal US can demonstrate Dandy-Walker malformation and variant, but caution should be exercised, since the developing normal cerebellum can mimic hypoplasia.
Angiography
Findings: X-ray angiography can demonstrate angiographic features of Dandy-Walker malformation. In the arterial phase, the posterior cerebral vessels are elevated. The superior cerebellar arteries are displaced anterosuperiorly above the posterior cerebral arteries. The posterior inferior cerebellar arteries (PICAs) are shortened, with high tonsillar loop. The inferior vermian branches of the PICA are absent. In some patients, the entire PICA is absent or hypoplastic. In the venous phase, arteriography shows absence of the inferior vermian veins, elevation of the great vein of Galen, and high position of the transverse sinuses.
| Treatment/Management |
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Medical Care:
Physical therapy is often used to help patients improve their abnormal motor functioning. However, many individuals will still continue to have difficulty walking and have poor balance. Another treatment is to give medication to reduce seizures. Seizures are involuntary muscle movements and/or decreased awareness of the environment due to overexcitement of nerve cells in the brain.
Surgical Care:
Treatment usually consists of a shunt to treat associated hydrocephalus. The neurosurgeon can shunt the cyst (cystoperitoneal), the ventricles (ventriculoperitoneal), or both.
To treat the buildup of fluid in the head, a flexible tube called a shunt can be placed in the ventricles of the brain, the inside of the brain, or the posterior fossa (the indented bone in the lower, back part of the skull). From one of these areas, the tube will drain the extra fluid into the space between layers that line the belly. The fluid will then be absorbed along the wall of the belly.
The shunting procedure will decrease the pressure in the head and will thus prevent the head from widening further. Sometimes, more than one tube needs to be placed, such as a tube in a ventricle and a tube in the posterior fossa. If these two spaces are not connecting, the surgeon will connect the tubes to a common valve that drains the fluid.
Unfortunately, the cyst cannot be removed with surgery because it already has blood vessels that go through it and connect to the brain. Taking out the cysts would thus cause too much damage to the brain.
Medication:
No medication could treat this congenital malformation although there are medications that can treat underlying problems.
Diet:
No specific regimen for the malformation. The diet is based on the associated problems of DWS.
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Deterrence/Prevention:
Some cases of congenital brain defects can be prevented with good maternal nutrition, including folic acid supplements. Folic acid is a vitamin that has been shown to reduce the incidence of neural tube defects. The Centers for Disease Control and Prevention recommends that all women of childbearing age consume 0.4 mg of folic acid daily to prevent neural tube defects. All over-the-counter multivitamins contain this amount of folic acid. Pregnant women should avoid exposure to infection, especially during the first trimester. Abstention from drugs and alcohol during pregnancy may reduce risk. Genetic counseling is advisable for parents who have had one child with anencephaly, since the likelihood of having another is increased.
Complications:
The list of complications that have been mentioned in various sources for Dandy-Walker Syndrome includes:
· Hydrocephalus
· Raised intracranial pressure
· Polydactyly
· Papilloedema
· Syndactyly
Prognosis:
The prognosis for patients with Dandy-Walker syndrome is only moderately favorable, even when the hydrocephalus is treated early and correctly. The presence of multiple congenital defects may adversely affect survival. Prognosis for normal intellectual development is variable depending on the severity of the syndrome and associated malformations.
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Medical/Legal Pitfalls:
· Failure to diagnose Dandy-Walker malformation with hydrocephalus in a neonate or a child can cause serious neurologic complications.
· Faulty diagnosis, such as mega cisterna magna or arachnoid cyst instead of Dandy-Walker malformation, can cause morbidity and mortality.
Special Concerns:
· US can be performed during pregnancy, and the diagnosis of Dandy-Walker malformation can be made antenatally. To confirm the diagnosis and gain detailed information, MRI evaluation can be used antenatally.
· Genetic counseling may be needed because a familial occurrence has been reported. Fetal karyotyping also is recommended for chromosomal analysis.
| References |
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Medfriendly.com
Health of Children
eMedicine
WrongDiagnosis.com
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