Neurosurgical Consultants: Brain Disorders: Congenital Anomalies: Dandy-Walker Malformations

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DANDY-WALKER MALFORMATION (CYST)

Dandy-Walker Malformations (or cysts) are developmental malformations in which the 4th Ventricle appears as a "Cystic" structure. This is a defect involving the Cerebellar Vermis, which may be partially or completely absent, with resulting dilation of the 4th Ventricle which becomes a "Cyst". It is thought that the defect results from abnormal embryogenesis of the roof of the 4th Ventricle. A milder form is termed the "Dandy-Walker Variant". This disorder may account for approximately 5% to 10% of cases of Ventriculomegaly (enlarged Ventricles).

DIAGNOSIS

In newborns, the diagnosis can be confirmed by CT or ultrasound.

Sonographic Characteristics of Dandy-Walker Malformation

A Cerebellar Vermis defect (complete or partial). The defect is inferior in partial conditions.

A posterior fossa cyst representing a dilated fourth ventricle.

Enlargement of the Cisterna Magna (representing the fourth ventricle).

Splaying of the cerebellar hemispheres

Ventriculomegaly.

The diagnosis can also be made by identifying the superior displacement of the Lateral Sinus groove on plain x-rays, or by transillumination of the Posterior Cranial Fossa.

Brain Scan & Time of Diagnosis

While many of these patients undergo investigation as newborns, many others develop normally through childhood and may only develop symptoms later in adolescence or early adulthood. Some patients are identified incidentally when undergoing a Brain scan for some other reason such as head trauma.

Figure 1: CT scan (Transaxial View) Dandy-Walker Cyst
This is a Dandy Walker Cyst in a 37 year old female with a 3 month history of increasingly severe headache and increased clumsiness with dysequilibrium. She also had experienced some numbness of the Left thumb & Index fingers.
She did not have Hydrocephalus.
Treatment consisted of a "keyhole" Posterior Cranial Fossa Craniectomy, resection of the Arachnoid Membranes and "shunting" of the Cyst to the peritoneal cavity (a Cyst-Peritoneal Shunt).
Her symptoms were completely relieved.

TREATMENT

For the majority of those patients who were incidentally identified and who are asymptomatic, no treatment is required.

For symptomatic patients, the most effective treatment incorporates the partial resection of the Arachnoid membranes that constitute the "lining" of the Cyst accompanied by the simultaneous insertion of a "shunt" to divert the CSF to the peritoneal cavity from where the fluid can be harmlessly reabsorbed. The resection of the membranes and the intracranial placement of the "shunt" tubing can be accomplished using Minimally Invasive Microendoscopic techniques.

In the event that Hydrocephalus is present, this usually requires a "shunt" of the Lateral Ventricles.

ASSOCIATED ANOMALIES

Other anomalies associated with Dandy-Walker Malformation include agenesis of the Corpus Callosum, Aqueduct of Sylvius stenosis, microcephaly, encephalocele, gyral malformations and Lipomas, cardiac & urinary tract anomalies, polydactyly (extra digits); facial malformations and chromosomal problems.