Cerebellar hypoplasia

Cerebellar hypoplasia is largely a descriptive term that encompasses a wide range of conditions, including congenital morphological cerebellar abnormalities and acquired changes that result in the cerebellum having reduced volume, stable over time ^1,4,5. The pattern of volume loss may be regional (affecting only part of the cerebellum) or global. 

Terminology

Cerebellar hypoplasia is divided by many into primary (congenital) and secondary (acquired) forms, although distinguishing between the two is not always possible ^3,5.

In some cases, global cerebellar hypoplasia can appear indistinguishable from diffuse cerebellar atrophy on a single study. It can only be distinguished from the latter by demonstrating or implying (clinically) that there has been no change over time ⁴. 

Clinical presentation

The clinical presentation is different, varying from normal to severe bilateral spastic cerebral palsy, intellectual disability, seizures, microcephaly and sensorineural hearing loss ².

Pathology

Given the heterogeneity of conditions included in the term cerebellar hypoplasia, it is unsurprising that the underlying pathology is also variable.

The primary causes of global cerebellar atrophy are chromosomal abnormalities (trisomy 13 and trisomy 18), metabolic disorders, genetic syndromes, and migrational disorders while congenital infections (cytomegalovirus followed by rubella and varicella viruses) are considered as secondary causes ³.

Radiographic features

All imaging modalities show a reduction in size and volume of parts of, or the entire, cerebellum with variable degrees of enlargement of adjacent CSF spaces. The pattern will vary and imaging features will help identify the underlying cause/condition, which are discussed separately ^3,5.

• global cerebellar hypoplasia

  • chromosomal abnormalities (e.g. trisomy 13 and trisomy 18)

  • genetic disorders

    • CHARGE syndrome

    • Cri du chat syndrome

    • neurofibromatosis type 1

    • Ritscher-Schinzel syndrome

    • and many more... ^3,5

  • metabolic disorders

    • mitochondrial disorders (e.g. Leigh disease, pyruvate

      dehydrogenase deficiency)

    • mucopolysaccharidoses (types I and II)

    • Smith-Lemli-Opitz syndrome

    • Zellweger syndrome

• unilateral cerebellar hypoplasia

  • PHACES syndrome

  • familial porencephaly

• pontocerebellar hypoplasia

  • acquired (e.g. cerebellar agenesis, severe prematurity)

  • congenital muscular dystrophy (e.g. Fukuyama disease, muscle-eye-brain disease, Walker-Warburg syndrome)

  • cortical malformations (e.g. lissencephaly, primary microcephaly, polymicrogyria)

  • genetic disorders (e.g. CASK mutation, cerebellofaciodental syndrome)

  • metabolic diseases (e.g. congenital disorders of glycosylation)

  • pontocerebellar hypoplasia of Barth

• vermian hypoplasia

  • genetic disorders

    • acrocallosal syndrome

    • Beckwith-Wiedemann syndrome

    • Gillespie syndrome

  • malformations

    • Dandy Walker malformation

    • isolated inferior vermian hypoplasia

    • pontine temental cap dysplasia

    • vermian aplasia (Joubert syndrome)

    • rhombencephalosynapsis

Differential diagnosis

• diffuse cerebellar atrophy: progressive loss of volume

• Blake pouch cyst

• mega cisterna magna

• arachnoid cyst in the posterior fossa