Unclassified Cerebellar Dysplasia

Definition 
• Focal or diffuse dysplasias of cerebellar hemispheres or vermis not associated with other known malformations or syndromes
○ Excludes Dandy-Walker spectrum, Lhermitte-Duclos disease, rhombencephalosynapsis, molar tooth malformations, congenital muscular dystrophies, syndromic (e.g., PHACES)
○ Excludes infectious (e.g., cytomegalovirus), metabolic etiologies (including inherited, e.g., congenital disorders of glycosylation-1a)

Diagnostic criteria
• Asymmetry or focal disruption of cerebellar folial and sulcalmorphology
○ Sometimes frank cleft is present
• Bumpy gray-white matter interface in cerebellum
• Lack of normal arborization of white matter
• Abnormal hyperintense signal in subcortical white matter → cyst-like foci
• Cerebellar gray matter heterotopia
• Enlarged and vertically oriented fissures
• Disordered foliation


PATHOLOGY
• Cerebellar cortex does not assume adult-like histology prior to age 1
• In 1 study of 147 normal infants, minor cerebellar dysplasias were identified in close to 85%
○ Some minor dysplasias involute after 9 months of age


CLINICAL ISSUES
• Hypotonia, microcephaly, speech delay

DIAGNOSTIC CHECKLIST
• Assess for "cobblestone" lissencephaly and congenital muscular dystrophy when considering diagnosis of isolated cerebellar dysplasia
• Look for and document associated posterior fossa and supratentorial lesions
• Small cerebellar hemisphere in fetus may reflect dysplasia


Best imaging tool
○ MR

Protocol advice
○ Use thin-slice profile T2WI in axial and coronal planes to define cerebellar morphology

Consider
• Assess for "cobblestone" lissencephaly and congenital muscular dystrophy when considering diagnosis of isolated cerebellar dysplasia

Reporting Tips
• Look for and document-associated posterior fossa and supratentorial lesions

Imaging gallery

Coronal FLAIR MR in a 5 year old with developmental delay and right hemiparesis shows agenesis of the corpus callosum with focal dysplasia of the left cerebellar hemisphere. Note the abnormal foliation in the small affected hemisphere  compared to the normal right side.

Axial T2WI MR in the same patient shows the distorted and disorganized pattern of white matter in the dysplastic left hemisphere in comparison with the normal right cerebellum (folia should be parallel to calvaria in axial plane).

Coronal T2WI MR in a child with vermian hypoplasia shows disordered foliation  in the right hemisphere and a prominent vertical fissure on the left . These disorders are thought to most likely be disruptions due to prenatal injury.

Coronal T2WI MR in a 4-year-old boy with global developmental delay shows a very abnormal cerebellum with vertically oriented folia and fissures along with nodular areas of gray matter, likely cerebellar heterotopia.