Cerebelo

The Fetal Cerebellum: Development and
Common Malformations
Catherine Garel, MD1, Catherine Fallet-Bianco, MD2, and
Laurent Guibaud, MD, PhD3
Abstract
The cerebellum undergoes a protracted development, making it particularly vulnerable to a broad spectrum of developmental
events. Acquired destructive and hemorrhagic insults may also occur. The main steps of cerebellar development arereviewed.
The normal imaging patterns of the cerebellum in prenatal ultrasound and magnetic resonance imaging (MRI) are described with
emphasis on the limitations of these modalities. Because of confusion in the literature regarding the terminology used for
cerebellar malformations, some terms (agenesis, hypoplasia, dysplasia, and atrophy) are clarified. Three main pathologic settings
are consideredand the main diagnoses that can be suggested are described: retrocerebellar fluid enlargement with normal or
abnormal biometry (Dandy-Walker malformation, Blake pouch cyst, vermian agenesis), partially or globally decreased cerebellar
biometry (cerebellar hypoplasia, agenesis, rhombencephalosynapsis, ischemic and/or hemorrhagic damage), partially or globally
abnormal cerebellar echogenicity(ischemic and/or hemorrhagic damage, cerebellar dysplasia, capillary telangiectasia). The appropriate
timing for performing MRI is also discussed.
Keywords
cerebellum, prenatal diagnosis, ultrasonography, Dandy-Walker malformation, agenesis, hypoplasia, dysplasia, atrophy
Received April 19, 2011. Received revised July 18, 2011. Accepted for publication July 21, 2011.
The cerebellum is one of theearliest cerebral structures to
develop. Its development is particularly protracted since cellular
proliferation, migration, and maturation extend into the first
postnatal months. Therefore, the cerebellum is particularly
vulnerable to a broad spectrum of developmental events.
Cerebellarmalformations are commonly observed during prenatal
ultrasonographic screening. There is a lack ofconsensus
regarding the terminology used and the description and mechanisms
of the different entities, and therefore literature about this
topic can be somewhat confusing. The aim of this article is to
clarify the main types of cerebellar malformations and to suggest
appropriate terminology that should be used to describe them.
It would help to clarify matters for both physicians and families.The main steps of cerebellar development will be reviewed,
and the normal imaging pattern of the fetal cerebellum in ultrasonographic
and magnetic resonance imaging (MRI) will be
described. In the third part, 3 different pathologic settings will
be described, making it possible to survey the great majority of
cerebellar malformations.
Cerebellar Development
Morphogenesis of the CerebellumAfter its closure, the rostral part of the neural tube corresponding
to the future brain, develops rapidly and undergoes
dilations, constrictions and flexures resulting in the formation
of 3 primary brain vesicles: the prosencephalon (forebrain), the
mesencephalon (midbrain) and the rhombencephalon (hindbrain),
the latter being separated from the mesencephalon by
the cephalic flexure and fromthe spinal cord by the cervical
flexure. By the fifth-sixth gestational week, the pontine flexure
separates the rhombencephalon into the metencephalon and the
myelencephalon and results in a transverse fold in the rhombencephalic
roof, the plica choroida that invaginates in the
fourth ventricle forming the choroid plexus.1 The plica choroida
divides the roof of the fourth ventricle into ananterior
membranous area and a posterior membranous area. The anterior
membranous area develops, giving rise to the cerebellar
vermis; it eventually disappears leaving the choroid plexus
attached to the inferior surface of the cerebellum. As a result
1 Service de Radiologie, Hoˆ pital d’Enfants Armand-Trousseau, Paris, France
2 Service de Neuropathologie, Hoˆ pital Saint-Anne, Paris, France...