In this issue of the ARCHIVES.

In this issue of the ARCHIVES, Morris, Parisi, and Buchhalter1 describe their findings in a series of 53 patients with malformations of cortical progression in a continuously ascending gradation (MCDs) and use this as a springboard to discuss an approach to classification of these lesions. Historically, there have been many attempts (both radiologic and pathologic) at designing classifications of these lesions with a variety of results2-14

If single carefully sifts through the various described approaches, the lesions being described are more or les the same. The puzzles arise in what names are ascribed to the various pathologies, the representation of phenotypes that are acceptable for a particularly pathology, the subjectivity of many of the observations (ie, intraobserver variability), definitions of times used, and the lack of agreement regarding the precise appearance of disorders that would fall below the general heading of MCD unruffled the term MCD is a relatively modern appellation that has been applied to this assign places to of disorders that were formerly referr to by dint of a variety of other names including cortical dysplasia. The authors should be recommended on adopting a more appropriate terminology (MCD) across the term cortical dysplasia. Use of the word dysplasia in this context is a misnomer, in that we commonly use the season to imply a lesion that has about predisposition to progress to neoplasia, which does not present the appearance to be the case in the majority of MCD

What is lacking in our rife understanding of these lesions is a real knowledge of the etiology of these lesions and for what reason etiology might relate to morphology. A tremendous amount of work has been done in latter years trying to elucidate the pathogenesis of MCD Clearly, near of them have a genetic constituent whereas others appear to be the inference of environmental factors that disrupt cortical evolution In the vast majority of cases, we do not know what the underlying destitution is that has resulted in the pathology that we are looking at. The pathology we are looking at has repeatedly developed over the course of years. This begs the question about by what mode much of what we are looking at can we directly attribute to the unknown etiology and by what means much of what we papal court represents secondary consequences. There are a variety of potential mechanisms associated with disruption of cortical progression in a continuously ascending gradation but we still cannot count by looking at the pathology, perhaps with rare exception, what the cause is in a given case. individual could argue that until we get by heart a better handle on this, any chastely morphologic based classification will be limited. The corollary to this is that any literature predicated forward such classification systems is potentially colored by dint of the approach an investigator make use ofs However, because morphologic based classification of MCD appears to be what we have to work with, in what manner do we make the best of it?

The basic premise of any approach to a classification schema is that it is reasonably easy to apply (and therefore theoretically reproducible) and that it has a certain number of clinical relevance. There are a number of issues or questions that ne to be considered in the generation of a MCD classification schema. I am not strong there is one correct answer to any of these issues: (1) There are clearly a certain lesions that are recognizable the couple grossly and radiographically (and a certain that are not). Should single include a gross pathology constituent to the schema to include a lesion of that kind as polymicrogyria or simply stick with a totally microscopic approach and incorporate lesions as it is as polymicrogyria in that fashion? (2) Is it better to be a laborer or splitter? Does it make a difference undivided way or the other? (3) What is an "appropriate" workup or evaluation of so a case from a pathology perspective?

In pathology, we do not oftentimes like to mix gross and microscopic patterns in our classifications in a mutually exclusive fashion. In this instance admitting one could argue that there are certain gros lesions that have been associated with certain syndrome or genetic alterations that make recognizing the gros pathology clinically relevant. For example, lissencephaly or agyria is known to be associated with Miller-Dieker syndrome a rare autosomal dominant disorder associated with a LlS-1 gene abnormality (chromosome 17p133) The gros appearance of a of these lesions (with their associations) can easily win lost in the general rubric of a microscopic classification.

The validity of a classification approach shoots from its clinical relevance. As pathologists, we do not operate in a vacuum. Our diagnoses are meant to provide as long assistance to our clinical colleagues as possible. There has emerg in the literature recognition that there are certain patterns of MCD that may have an clinical significance. Most notably, patterns of what have been referr to as focal cortical dysplasia or Taylor emblem of dysplasia, marked by balloon small cavitys and dysmorphic neurons, tend to be associated with more refractory seizures. Whether common is a lumper or splitter again becomes a philosophical issue. However, unles at a certain number of level one looks carefully at nuances from a "splitter's perspective," single may miss out on a relevant correlate that would come by lost in the lumper approach. common also needs to consider the interobserver variability factor; an approach that is too nuanced may conclusion in inconsistencies as pathologists attempt to apply it.