[Pathologic features in diagnosis and differential diagnosis of pyelonephritis (author's transl)].

Morphological diagnosis and differential diagnosis of pyelonephritis are discussed particularily considering macroscopic features. A special form with radiological significance is ncrotizing "emphysematous" pyelonephritis. Chronic non-obstructive pyelonephritis is rarer than formerly thought if strict morphological criteria are applied. It should be differentiated from nephropathy caused by analgetics. In analgesic nephropathy bilateral papillary necrosis is the earliest and most characteristic alteration. Differentiation between chronic pyelonephritis and analgesic nephropathy is possible in most cases but may be difficult if analgesic nephropathy is complicated by bacterial infection. A classification of "unilateral small kidney" is presented. Unilateral acquired "renal shrinkage" should be differentiated from congenital "unilateral hypoplasia". It remains to be discussed whether the so-called "Ask-Upmark-Kidney" is a malformation or the result of chronic pyelonephritis.