Clinical History
Term baby with anormal brain ultrasound.
Imaging Findings
CT (Figure 1) and MRI (Figures 2, 3) shows a large posterior Fossa cyst. It is agenesis of the corpus callosum with a ventricular colpocephaly. Eventration of the superior vermis remnant, the vallecular opening of the fourth ventricle into the cyst, absence of the inferior vermis and underdevelopment of the lateral cerebellar hemispheres. There is an expanded posterior fossa with a High riding tentorium best show in midline sagittal images (Figure 4). There is an elevated brainstem with small caliber base of the pons.
Discussion
Dandy-Walker malformation (DWM) is considered an uncommon congenital malformation in the posterior fossa, that affects 1/25 000– 30, 000 live births [3]. This malformation consists about a cystic enlargement of the fourth ventricle, hypoplasia and upward rotation of the vermis cerebelli, and an enlarged posterior fossa with a cranially shifted position of the lateral sinus, tentorium, and torcula herophili. [2]
DWM may be associated with another central nervous system (CNS) defects as atresia of the foramen of Magendie and Luschka, corpus callosum agenesis (21%), cerebral gyral malformation (21%), holoprosencephaly (10%), diencephalic cysts (10%), and posterior fossa meningomyelocele (10%) [1].
Dandy-Walker malformations are formed during embryogenesis, at 7 to 10 weeks of gestation, by the perturbation of the development of the cerebellar hemispheres and the fourth ventricle. The cause of the insult is unknown[1].
The Dandy-Walker complex has an extensive variability of phenotypic expression, making hard and, sometimes, possible eluded. The macrocephaly, as an always present sign, associated with any other neurological sign forces the detailed exploration of CNS [2].
Evaluation of posterior cranial fossa abnormalities is the first start in an accurate fetal US study, but Fetal MRI is highly specific. Multiplanariety allows the visualization of the brain structures, evaluate the cerebellar biometry and associated defects. Some studies recommend that DWM, with the upward displacement of a dysplastic/hypoplastic vermis, is associated with the expansion of the cistern Magna and "tail sign" in the total cases [4]. The ‘tail sign’ is a linear hypointensity on T2 images in equivalence with the lower part of the vermis, which agrees histologically to a thickness of the fourth ventricle roof that seems raised and dysplastic. The "tail sign" could be appropriate in the difficult differential diagnosis between Dandy-Walker, vermian hypoplasia, vermian malrotation, and vermian partial agenesis [4].
Decompressing the foramen magnum by the resolution of hydrocephalus or the drainage of the cyst of the posterior fossa or both would be appropriate to attend the impaction at this level with an excellent postoperative result [3]. Despite intraoperative evidence of distal shunt failure, it proved to be ineffective and direct shunting of the posterior cranial fossa cyst was required.[3]
Written informed patient consent for publication has been obtained.
Differential Diagnosis List
Dandy Walker Malformation plus agenesis of the corpus callosum.
Megacisterna magna
Joubert anomaly
Final Diagnosis
Dandy Walker Malformation plus agenesis of the corpus callosum.
