DIFFERENTIATING the congenital small kidney from the acquired, atrophic kidney, either clinically or pathologically, may be extremely difficult.1-5 Small kidneys have been indiscriminately described as atrophic, hypoplastic, dysplastic, aplastic, contracted, or infantile, terms which encompass a conglomeration of congenital abnormalities and acquired diseases, each of which may result in diminution of renal size.
Abnormalities in the amount of renal tissue (hypoplasia) and anomalies of kidney differentiation (dysplasia)5, although imperfectly understood and categorized, comprise the congenital small renal masses which may be confused with acquired shrunken, hydronephrotic, ischemically contracted or advanced pyelonephritic small kidneys. The patient's history or clinical course will often corroborate a radiographic interpretation of acquired renal contraction or the more gross dysplastic processes. However, in a number of situations, neither clinical or laboratory findings nor the radiographic appearance of the kidney on intravenous pyelography can resolve the problem of the etiology of a small kidney.
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