What to Call Hypoplastic Kidney?*

Among the congenital abnormalities of the urinary tract, the term hypoplastic kidney is one of the least well defined and also one of the most widely used. Certain abnormal structures are sometimes called hypoplastic kidneys and certain abnormal kidneys which we term hypoplastic are called by some aplastic (even agenetic) kidneys, dysplastic, congenital atrophic, miniature, or infantile kidneys, doll's kidneys, dwarf or dwarfed kidneys. If the term hypoplastic is to be retained it should be reserved only for those kidneys which are underdeveloped due to some deficiency, both quantitative and qualitative, in their fundamental components. Among hundreds of bizarrely-shaped or oddlooking kidneys, all diminutive in size, some seem to answer this definition and present a set ofcommon anatomical features suggesting that they may result from similar embryonic defects. They all present themselves as more or less functional kidneys, diminutive in size and weight, because of a quantitative and a qualitative deficiency in their ureteric and metanephric primordia. Their minor calices are both less numerous and less developed than normal, so that in consequence the pyramids, lobes and successive generations of nephrons that have grown from them are scarce and underdeveloped. When the defect is unilateral such a kidney is unable to sustain life without the help of a mate; when bilateral they prove sooner or later to be fatal. Histologically, such structures necessarily contain more or less differentiated nephrons; otherwise they would not be kidneys. Whether or not the term hypoplastic is to be kept and reserved for this family is one question. There is a second more important question, however: 'Should some small kidneys of bizarre shape be ranged under one unique family name?'-whether this name be hypoplastic, meroplastic, ateleplastic, elleipoplastic, or any better term from Greek, until the right word springs from aetiopathogenesis through histology or embryology?