Rare/Regional Variants

Abstract

Rare malformations and regional variants are relative terms. While it is generally easy to distinguish between rare and common, it is difficult to define the border between the rare and the not-so-rare. As far as anorectal malformations (ARM) are concerned, the problem is compounded by the vagaries of space and time. Lesions that are nonexistent or super-rarities in one part of the world are common in another part. Lesions that were common at one period of time become rare in the same part of the world at another period of time. Nevertheless, many varieties of ARM are seen universally and have been seen over several decades; these varieties merit the name “common” and will not be discussed in this chapter.