Dandy-Walker malformation: prenatal diagnosis and prognosis

The difficulty in prognosticating the clinical and intellectual outcome of fetuses presenting with a Dandy-Walker malformation (DWM) comes from the great variety of cystic, median, and retrocerebellar malformations that probably have nothing in common and the variability of the definitions given to these lesions. In addition, many of these lesions can mimic each other. A correct diagnosis cannot be made without a good quality MRI including sagittal views of the vermis and T2-weighted images. We limited the diagnosis of DWM to those malformations with all of the following features: 1) a large median posterior fossa cyst widely communicating with the fourth ventricle, 2) a small, rotated, raised cerebellar vermis, 3) an upwardly displaced tentorium, 4) an enlarged posterior fossa, 5) antero-laterally displaced but apparently normal cerebellar hemispheres, 6) a normal brain stem. If any one of the previous criteria were not met, the malformation was considered distinct from DWM.

The charts of 26 patients with DWMs (18 females and 8 males; median age 10.5 years) were reviewed retrospectively. The diagnosis of the malformation was made prenatally in 7 children and postnatally in the 19 others. All the patients had both one MRI including axial and sagittal views of the posterior fossa as well as T1- and T2-weighted sequences, and one neuro-psychological investigation. Syndromic DWMs and Dandy Walker variants were excluded from the study. MRIs were reviewed in a blinded manner looking for brain malformation or damage and studying with particular attention the anatomy of the vermis. Systemic malformations were also recorded. Developmental quotient (DQ) and intellectual quotient (IQ) were said to be normal when equal or greater than 85, and low when below this value. Statistical analysis was performed using a Fisher test to analyze the relationship between intellectual performances, vermis anatomy, ventricular size, brain anatomy, and associated malformations.

On scrutiny of sagittal T2 sequences, the vermis, although constantly small, rotated, and pushed towards the tentorium presented as two distinct morphologies, leading us to distinguish two groups of patients. In the first group (n=21), the vermis presented with two fissures, three lobes, and a fastigium as in the normal situation. In this particular group, none of the patients had associated brain malformation and all but 2 were functioning normally. One of the 2 retarded children had a fragile X syndrome. The other had a severe periventricular leukomalacia due to prematurity, which, per se, was sufficient to account for mental delay. In the second group (n=5), the vermis was highly malformed, obviously dysplastic, presenting with only one fissure or no fissure at all. It was constantly associated with major brain anomalies, most often a complete corpus callosum agenesis. All the patients in this group were more or less severely retarded. Vermis anatomy in DWMs was statistically correlated to neurological and intellectual outcome. Is the vermis dysplasia responsible, in itself, for this poor outcome? No answer can be given from this series, because retardation was observed in children who always had both a severely dysplastic vermis and other brain malformations. No other patient-related factor was statistically correlated to the outcome, in particular, hydrocephalus and extracerebral malformations.

We described two types of DWM. The most frequent is characterized by an isolated and partially agenetic vermis. This malformation is compatible with a normal life. The second type consists of a severely abnormally lobulated vermis and associated brain malformation. This malformation is always accompanied by mental retardation.