E2679. Not Dandy Walker Variant: A Review of Prominent Retrocerebellar CSF Space in Children for the General Radiologist
  1. Tracee Wee; University of British Columbia
  2. Neekita Gupta; Children's Hospital of Eastern Ontario
  3. Anvita Pauranik; British Columbia Children's Hospital
Prominent retrocerebellar cerebrospinal fluid (CSF) space can be frequently encountered on pediatric neuroimaging studies. With abnormal vermian development, when the imaging does not meet the classic definition of Dandy Walker malformation (DWM), the term “Dandy Walker variant or continuum” has been used historically to describe the aberrant posterior fossa development. However, this terminology is no longer recommended. Instead, the emphasis is on a more elaborate description of the findings in the posterior fossa. Moreover, combining the findings in the supratentorial brain can occasionally predict certain neurogenetic disorders which mimic DWM phenotype. The purpose of this exhibit is to demonstrate and differentiate the imaging features of various entities that result in an enlarged retrocerebellar CSF space, such as inferior vermian hypoplasia (IVH) and several neurogenetic conditions.

Educational Goals / Teaching Points
The term “Dandy Walker Continuum or variant” should be avoided and instead an accurate anatomic descriptor should be used. IVH presents with a prominent posterior fossa CSF space with an enlarged caliber of the fourth ventricle, previously termed as Dandy Walker Variant. Several neurogenetic conditions may have aberrant vermian development and present with prominent retrocerebellar fluid space. Assessment for associated anomalies including supratentorial findings is helpful for diagnosis.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
When encountering prominent retrocerebellar CSF space, the first step is to assess the vermis. If the vermis is normally developed, look for signs of any mass effect or compression. If present, this reflects an arachnoid cyst. Normal vermis, without any mass effect, most commonly represents mega cisterna magna (MCM), which is a normal anatomic variant. IVH presents as a prominent retrocerebellar fluid space with small-sized inferior vermis and normal-sized posterior fossa. Posterior fossa brain malformations, Hemangiomas, Arterial anomalies, Coarctation of the aorta and cardiac defects, and Eye abnormalities (PHACE) syndrome can mimic DWM on the sagittal midline image. Asymmetric cerebellar hypoplasia and enlarged Meckel’s cave can point to the diagnosis of PHACES. Several neurogenetic disorders may have prominent retrocerebellar CSF space, mimicking DWM, which may be secondary to reduced size of the posterior fossa structures. Therefore, it is important to assess pontine size when encountering a small vermis. Enlargement of the retrocerebellar fluid space can also be secondary to destructive events in utero such as cerebellar hemorrhage or stroke. Occasionally, accurate diagnosis cannot be predicted by imaging alone requiring neurogenetic workup.

Multiple developmental pathologies can result in an enlarged retrocerebellar CSF space and may have similar appearances. Careful and systematic evaluation of the associated structural abnormalities are necessary to identify the most appropriate diagnosis and differentiate them from true DWM.