Dandy-Walker malformation: prenatal diagnosis and prognosis
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- Klein, O., Pierre-Kahn, A., Boddaert, N. et al. Childs Nerv Syst (2003) 19: 484. doi:10.1007/s00381-003-0782-5
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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.
Materials and methods
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.
KeywordsDandy-Walker malformationPrognosisPrenatal diagnosisCongenital abnormalitiesCerebellar vermisIntellectual development
Nothing is more hazardous than to prognosticate the outcome of a fetus presenting with a cystic fourth ventricle. This is due to the great variety of malformations that probably have nothing in common, except for the existence of this cyst. The difficulty comes from the fact that the definitions given to these lesions do not always include the same features, and that many of these cyst-like anomalies can mimic each other. It is well known, for example, that any infracerebellar fluid collection, like arachnoid or neuro-glial cysts, can resemble a Dandy-Walker malformation (DWM) by lifting up the vermis, shifting laterally the tonsils, opening the foramen of Magendie, and even raising the tentorium. To improve the prenatal prognostication, an effort must be made towards more strict and precise definitions, better analysis of the prenatal imaging data, and, if possible, cooperative studies aiming for long postnatal follow-up of acceptable cohorts of patients. Nevertheless, the recent advances in prenatal imaging, mainly fetal MRI, have already much improved our knowledge, compared with when ultrasonography was the sole mode of imaging for fetuses.
Definitions and diagnostic problems
Dandy-Walker malformation is a very rare congenital malformation of the posterior fossa, with an incidence ranging between 1/25,000 and 1/35,000 births . This malformation was first described by Dandy and Blackfan in 1914 . Taggart and Walker reported on three new cases in 1942,  and Benda finally labeled the malformation as "Dandy-Walker" in 1954 .
The problem is that definitions have changed according to the diagnostic technique employed and have been modified to include findings discovered case by case. They variably included items like patency of the foramens of Luschka and Magendie, hydrocephalus, or CSF dynamics between the cyst and the subarachnoid pathways. The wide variation in the appearance of the cerebellar vermis on sagittal images and the variability of the terms employed to describe it (compressed, rotated, atrophic, hypoplastic, aplastic, agenetic) have also added to the confusion. In addition, any cystic lesion resulting in a large degree of vermian rotation may suggest, on axial images of CT scans or MRIs, the presence of a vermian hypoplasia or aplasia, despite the presence of a fully formed vermis. Sagittal views of the vermis are mandatory for studying precisely the content of the posterior fossa. CT scans with sagittal reconstruction are inadequate because of insufficient definition. For the moment, the same can be said of ultrasonography. For that reason, MRI with sagittal planes and T2-weighted images are necessary for diagnosis, and this applies to the fetus as well. A more precise analysis of the vermis could be reached by a three-dimensional MRI reconstruction with anatomical recognition of the vermian sulci but the necessary dedicated software  is not yet available.
Large median posterior fossa cyst widely communicating with the fourth ventricle
Rotated, raised, and small cerebellar vermis coming into contact with the tentorium
Upward displacement of the tentorium and lateral sinuses
Posterior bossing of the posterior fossa contributing to its enlargement
Knowing the inconsistency of hydrocephalus in DWMs, the size of the ventricles should not be taken into account in the definition.
Numerous malformations are mentioned in the literature in association with both DWMs and DW complex. They are neurologic, systemic, or genetic [3, 6, 7, 10, 12, 16, 17, 18, 21, 23]. These malformations are sometimes multiple in the same patient. Brain malformations include partial or total corpus callosum agenesis or hypoplasia, interhemispheric cysts, gyral anomalies, gray matter heterotopias, occipital meningoceles, malformations of the dentate nucleus and of the brainstem, and hamartomas. Systemic malformations may be cardiovascular (ventricular septal defects, patent ductus arteriosus, transposition of the great arteries, congenital pulmonary stenosis), urogenital (vesico-ureteral reflux, hydrocele, horse shoe kidney), intestinal (mega rectum, mega sigmoid, duodenal atresia), facial (strabismus, hypertelorism, facial angioma, cleft palate), or at the level of the limbs (malformed limbs, finger or toe syndactyly).
Prognosis of the Dandy-Walker malformation
In most previous series of DWMs, approximately 40% of the children were intellectually normal, 40% were severely retarded, and 20% were borderline. Some authors measured the ratio of cerebellar size to posterior fossa size on CT scans and found no correlation between it and intellectual development . Associated CNS and systemic abnormalities, seizures, and hearing or visual problems have been said to carry poor intellectual outcome  although Bindal et al. did not find that corpus callosum agenesis was correlated with a bad prognosis . These series, however, should be regarded with caution because they were published before the era of MRI, or included patients diagnosed on the basis of CT scans alone. As a consequence, all have true DWMs mixed with other types of infratentorial cystic malformations. This was the case, for example, with our own series published in 1984, in which almost one third of the diagnoses had to be revised after these patients had an MRI.
Compelled by the development of prenatal diagnosis and counseling and an increased demand for better and reliable prognostication of fetal abnormalities, we recently reviewed our cases of DWMs confining the study to only those patients who were investigated by MRI and had a neuropsychological investigation. These 26 patients were followed in our department from January 1990 to December 2001. Seven of them were diagnosed prenatally and 19 postnatally. All their MRIs included axial and sagittal views of the posterior fossa with T1- and T2-weighted sequences. Statistical analysis was performed using a Fisher test to analyze the relationship between intellectual performance and several parameters including vermis lobulation, hydrocephalus, brain anatomy, visceral anatomy, and karyotype. p values of <0.05 were considered significant.
Focusing our attention on the vermis anatomy, we found that the series comprised two distinct groups of patients.
Vermis anatomy and associated brain malformations were, in this series, the only patient-related factors statistically correlated with the outcome (p=0.002). It is noteworthy that hydrocephalus and systemic malformations were unrelated to the intellectual and neurological prognosis. Only 1 patient had an abnormal karyotype, making impossible the inclusion of genetics in the statistical analysis. However, common knowledge, and the fact that this child was extremely handicapped from both an intellectual and a neurological point of view, make it highly probable that genetics is relevant to prognosis. In any case, discovery of an abnormal karyotype in a fetus would certainly restrain us from giving optimistic prenatal counseling.
We must conclude from this study that there are two types of DWMs. One is compatible with a strictly normal life. The vermis in this case is only partially agenetic and the rest of the brain is apparently normal. The second type is, on the contrary, a major malformation carrying poor intellectual and neurological prognosis. This form is characterized by the association of a severely dysplastic vermis and associated brain anomalies, most often of the midline. Is the vermis dysplasia responsible, in itself, for this poor outcome? It has long been questioned whether the cerebellum, and the vermis in particular, play an important role in human behavior [1, 9, 11, 12, 13, 14, 17, 18, 20, 21, 22, 25, 26, 27]. No answer can be given from this series, because all of the children with a severely dysplastic vermis and mental retardation also had other brain malformations.
The malformation is a pure DWM and not one of the DW variants that probably correspond to completely different lesions
Prenatal investigations include a karyotype and a good fetal MRI with T2-weighted sagittal images allowing precise study of the vermis and supratentorial midline
An abnormal karyotype and severely dysplastic vermis, which almost certainly correspond to a grim prognosis, must lead to scrutiny of the supratentorial brain