DANDY-WALKER VARIANT (1,2)

ULTRASOUND

• Cisterna magna - normal.
• Partial vermian agenesis (usually inferior vermis).
• Fourth ventricle - lesser degree of dilatation.
• Posterior fossa volume - relatively normal.
• Lateral ventricles - no or minimal dilatation (24%).
• Extra CNS abnormalities (47%).
• Abnormal karyotypes (9%).

Normal superior cerebellum – no defect in the vermis
Defect in inferior cerebellar vermis with direct communication between IVth ventricle and cisterna magna

OTHER CAUSES OF INFERIOR VERMIAN DYSGENESIS

1. Sporadic.
2. Joubert's Syndrome (3).
• Familial vermian agenesis (more pronounced in the posterior inferior portion of the vermis). Normal cerebellar hemisphere + IV ventricle.
• Callosal agenesis; hydrocephalus.
• Occipital encephalocele.
• Polycystic kidneys or enlarged echogenic kidneys.
• Increased nuchal translucency in the first trimester is described (4).
• Abnormal movement (especially of the eye - nystagmus).
• Polydactyly and clubfoot.
• Episodic hyperpnea.
• Ataxia
• Mental retardation.
• AR inheritance with variable expressivity.

3. Down Syndrome

4. Walker-Warburg Syndrome
5. Cerebro-oculo-muscular syndrome.
6. Less frequently:
• Meckel-Gruber Syndrome.
• Ellis van Creveld.
• Coffin Siris Syndrome.
• Dominant X Linked Aicardia Syndrome.
• Cornelia de Lange Syndrome.

FALSE POSITIVE DANDY-WALKER VARIANT

The false impression of a defect in the inferior vermis may be created by visualizing the cerebellum at a steep angle. By reorientation the transducer angle the true cerebellar vermis may be assessed.

Defect in the inferior vermis corrected by correcting the transducer angle

REFERENCES

1. Laing F, Frates M, Brown D et.al. Sonography of the fetal posterior fossa: False appearance of mega cisterna magna and Dandy-Walker variant. Radiology 1994;192:247-251.
2. Estroff J, Scott M, Benacerraf B. Dandy-Walker variant: prenatal sonographic features and clinical outcome. Radiology 1992;185:755-758.
3. Ni Scanaill S, Crowley P, Hogan M et.al. Abnormal prenatal sonographic findings in the posterior cranial fossa: a case of Joubert's syndrome. Ultrasound Obstet Gynecol 1999;13:71-74.
4. Reynders CS, Pauker SP, Benacerraf BR. First trimester isolated nuchal lucency: significance and outcome. J Ultrasound Med 1997;16:101-105.