Cerebellum—small brain but large confusion: A review of selected cerebellar malformations and disruptions

Abstract

Defining and classifying congenital disorders of the cerebellum can be difficult and confusing. One reason is that some abnormalities called "malformations" are not truly (primary) developmental malformations. This applies to Chiari I "malformations" as well as to Chiari II "malformations." The latter results mainly from a prenatal cerebrospinal fluid (CSF) leak. Also disruptive cerebellar lesions are not uncommon, examples being the "vanishing cerebellum" in myelomeningocele, cerebellar lesions in very low birth weight prematurely born infants, unilateral cerebellar hypoplasia/aplasia, and probably some instances of cerebellar agenesis (CA). The cerebellar hypoplasias consist of a heterogeneous group of inherited and prenatally acquired conditions. The concept of pontocerebellar hypoplasias will need to be expanded beyond the two main types (PCH-1 and PCH-2), and demonstrate that a classification system of cerebellar malformations cannot be based on neuroimaging criteria only. Additional studies are expected to show that this also applies to the molar tooth sign, which was initially described in Joubert syndrome (JS). The JS is the prototype of midhindbrain malformation, but its delineation is still unsolved. JS may well be an overdiagnosed entity; many cases likely not having JS are on record. Rhombencephalosynapsis (RS) has been increasingly diagnosed with the advent of neuroimaging. No familial cases have been observed. Although many affected individuals have variable impairments, RS can be found in children with normal cognitive function. In this review, some of the cerebellar anomalies are briefly discussed.

The Shrunken, Bright Cerebellum: A Characteristic MRI Finding in Congenital Disorders of Glycosylation Type 1a

“…Thus, cerebellar involvement in CDG-1a is probably best described as a combination of CA and CH, similar to pontocerebellar hypoplasia and other putative prenatal-onset degenerative disorders. 10,12,13 A consistent, striking finding in our series was the presence of high T2/FLAIR signal intensity of the involved cerebellar cortex and, often, the subcortical white matter. To the best of our knowledge, this is a novel finding in CDG1a, which we believe may be important in the differential diagnosis.…”

“…Conversely, CH is a congenital condition characterized by incomplete development of the cerebellum, in which the fissures are of normal size compared with the folia. 10 In practice, such differentiation is much less easy to achieve, particularly when a single MR imaging study is available. In our series, all patients exhibited a variably severe volume loss of the cerebellum at presentation, with involvement of both the vermis and the cerebellar hemispheres, which further progressed on follow-up.…”

Congenital Abnormalities of the Posterior Fossa

“…However, these cysts may be asymptomatic and discovered incidentally. Overall, children who undergo surgery and shunt placement have a favorable outcome (4,23).…”

“…Congenital posterior fossa anomalies may result from inherited (genetic) or acquired (disruptive) causes (4,5). A malformation is defined as a congenital morphologic anomaly of a single organ or body part due to an alteration of the primary developmental program caused by a genetic defect (6).…”

Epidemiology of central nervous system malformations in South-Eastern Hungary

“…The prevalence of cerebellar aplasia/hypoplasia is unknown. It has been described in context of several genetic and metabolic syndromes (69,73), therefore its population-based survey would be a great challenge. The clinical spectrum of our cases was similar to those ones reported by Wassmer et al (74).…”