Cerebellar hypoplasia
Synonyms and keywords:

# Overview
Cerebellar hypoplasia is a condition in which cerebellar volume is significantly reduced but its shape remains intact. It occurs in multiple diseases and has various patterns on neuroimaging. Variety of prenatal insults have been associated with cerebellar hypoplasia. Diagnosis of cerebellar hypoplasia can be made prenatally as well as postnatally. Prognosis and treatment of cerebellar hypoplasia largely depend upon the underlying etiology.

# Historical prespective
There is no available data on historical perspective of cerebellar hypoplasia.

# Classification
- Cerebellar hypoplasia may be classified according to  into  subtypes:
- Unilateral cerebellar hypoplasia
- Cerebellar hypoplasia with predominant involvement of vermis
- Global cerebellar hypoplasia involving both vermis and cerebellar hemispheres
- Hypoplasia involving pons along with cerebellum i.e pontocerebellar hypoplasia

# Pathophysiology
- The pathogenesis of cerebellar hypoplasia involves faulty neuronal proliferation and migration during embryonic nervous system development. It is related to multiple disease processes,which may include genetics mutations in certain genes involved in organization and maturation of fetal brain e.g Wnt family as well as other genes like En1 & 2, WDR 73, and chromosomal abnormalities especially trisomy 9,trisomy 13,trisomy 18.  Other disease processes associated with cerebellar hypoplasia include prenatal infections, prenatal exposure to teratogens, disruptive lesions, metabolic abnormalities..

# Causes
Cerebellar hypoplasia may be caused by variety of etiologies listed below in the table.
To review risk factors for the development of , click here.

# Differentiating cerebellar hypoplasia from other Diseases
- Cerebellar hypoplasia must be differentiated from cerebellar atrophy. Neuroimaging can help differentiate between the 2 entities. In case of cerebellar atrophy, there is loss of cerebellar parenchyma with subsequent expansion of interfolial spaces or fissures. While in cerebellar hypoplasia fissures have normal size relative to folia.  

# Epidemiology and Demographics
- From , the prevalence of cerebellar hypoplasia was estimated to be  cases per 100,000 births, in a study recruiting individuals from 10 states of Unites States. Prevalence of cerebellar hypoplasia increased overtime. From year 1997-2004, prevalence of cerebellar hypoplasia was estimated to be around 0.68 per 100,000 births while it raised to 2.00 per 100,000 births from year 2005-2011. In another study, a child neurologist reported that 0.4 %(11 out of 2500) of children visiting him had cerebellar hypoplasia. Another study recruiting 188 children with developmental delays reported that 4.5% of the study population had cerebellar hypoplasia. 

## Age
- Cerebellar hypoplasia may be detected in utero but as trans cerebellar diameter is not measured routinely in 3rd trimester so diagnosis is sometimes delayed to post-natal period. However, in case of pontocerebellar hypoplasia inutero diagnosis is considered difficult and it is mostly diagnosed after birth.

## Race
- There is no proven racial predilection for cerebellar hypoplasia. In a study, non-hispanic black maternal race was at a slightly increased risk of cerebellar hypoplasia but the results were statistically non-significant.

# Risk Factors
- Common risk factors in the development of cerebellar hypoplasia are low birth weight, preterm birth, multiple pregnancies, prenatal infections, prenatal use of anti epileptic drugs, maternal use of alcohol or cocaine. Maternal hypertension and maternal use of vasoactive medications have also been associated with increased risk of cerebellar hypoplasia but results were not statistically significant. Postnatal glucocorticoid use in preterm infants has also been associated with poor cerebellar development and maturation. 

# Natural History, Complications and Prognosis
- Prognosis of cerebellar hypoplasia generally depends upon the underlying etiology. Cerebellar hypoplasia associated with non-progressive disorders (e.g abnormal brain formation during fetal development), has a relatively better prognosis. On the other hand, cerebellar hypoplasia associated with progressive conditions has poor prognosis.

# Diagnosis

## Diagnostic criteria
There is no specific diagnostic criteria for cerebellar hypoplasia.

## History and Symptoms.
- Symptoms of cerebellar hypoplasia may include the following:
- Seizures
- Behavioral abnormalities
- Muscular hypotonia
- Tremors
- Microcephaly
- Poor/absent language/speech development
- Intellectual disability
- Headache
- Hearing impairment
- Dizzy spells

## Physical Examination
- Physical examination may be remarkable for:
- Truncal ataxia
- Hypotonia
- Abnormal ocular movements
- Intention tremors
- Speech/language abnormalities
- Developmental delay in children

## Laboratory findings
- There are no specific laboratory findings associated with cerebellar hypoplasia. Lab findings may be abnormal depending upon the underlying etiology.

## Electrocardiogram
There are no ECG findings associated with cerebellar hypoplasia.

## X-ray
There are no x-ray findings associated with cerebellar hypoplasia.

## Echocardiography
There are no echocardiographic findings associated with cerebellar hypoplasia.

## CT scan
Brain CT scan may be helpful in the diagnosis of  but MRI remains the diagnostic study of choice.

## MRI
MRI is the diagnostic study of choice for diagnosis of cerebellar hypoplasia. Findings on MRI suggestive of cerebellar hypoplasia include small trans cerebellar diameter, reduced cerebellar volume with intact cerebellar morphology, and prominent subarachnoid spaces. It can also identify one of the 4 patterns of cerebellar hypoplasia that include unilateral cerebellar hypoplasia, hypoplasia involving cerebellar vermis, hypoplasia involving both cerebellar hemispheres and vermis, pontocerebellar hypoplasia. Sometimes in pontocerebellar hypoplasia, cerebellar hemispheres are so profoundly involved that neuroimaging reveals a "dragonfly" appearance showing small flattened cerebellar hemispheres with relatively spared vermis. 

## Other Imaging Studies
Inutero ultrasonography can reveal reduced trans cerebellar diameter along with other findings suggestive of cerebellar hypoplasia.
Diffusion tensor imaging may be helpful in the diagnosis of cerebellar hypoplasia. Cerebellar microarchitecture and cerebellar white matter tracts along with their connections are ellaborated by diffuse tensor imaging. Disruptive lesions can be better identified using susceptibilty weighted imaging as it has high sensitivity for blood products and calcifications.

## Other Diagnostic Studies
There are no other diagnostic studies associated with cerebellar hypoplasia.

# Treatment
- There is no standard treatment for cerebellar hypoplasia; the mainstay of therapy is symptomatic and supportive care and largely depends upon the underlying etiology.

## Prevention
- There are no primary preventive measures available for .