To the Editor: We were very interested in the article “Analysis and Classification of Cerebellar Malformations” by Patel and Barkovich (1), and we thank the authors for their imaging-based classification of cerebellar malformations, which highlights an area of great confusion. This classification has an important value because it defines and helps in the recognition of some cerebellar malformations that have been less described in the radiologic literature.
We ask ourselves whether an imaging-based classification represents categories of similar malformations. Even if it is very helpful to understand these malformations, it may be artificial to separate a first category of “cerebellar hypoplasia” from “cerebellar dysplasias” because most of the malformations included in the latter category are associated with vermian hypoplasia. Moreover, to quote prenatal “cytomegalovirus” infection as an example, its etiopathogenesis and prognosis are probably not the same as the prognosis of “isolated diffusely abnormal foliation.” We think that a classification based on cerebellar embryology, genetics, or signaling molecules that play a role in specifying cerebellar domains (morphogenesis) but also in cellular migration (histogenesis) (1, 2) would better define different types of cerebellar malformations that are similar in terms of their consequences to brain function. Nevertheless, we agree that to obtain such classification is a very difficult task.
We were also very interested in and satisfied with the description and the recognition of focal and/or diffuse cerebellar cortical dysplasia as a new radiologically detectable cerebellar malformation. Although the pathology literature has already provided relevant information about its morphologic characteristics, it has recently been revealed by MR imaging and deserves note in the radiology literature. We agree that focal cortical dysplasia will be recognized more commonly, especially in patients with developmental disabilities. Even if the mechanism by which the dysplasia develops remains poorly understood, its recognition could probably be the first step to understanding its role.
The authors report that imaging findings in cases of cortical dysplasia and cerebellar heterotopia have not been previously described and that, moreover, they do not have histologic details of isolated focal cerebellar dysplasias. We bring to their attention our previous report of cerebellar cortical dysplasias already published in the AJNR (3) and our article concerning the neuropathologic description of a neonatal case of isolated focal cortical dysplasia associated with cerebellar heterotopia (4). Even if the pathogenesis of focal cerebellar cortical dysplasias is being investigated (4), its pathologic significance and the mechanism by which the same malformation that is often associated with more widespread brain anomalies could be, in other cases, an isolated finding remains unknown.
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