Natural History of Chronic Pyelonephritic Scarring

The large irregular scar seen in the natural specimen is nearly always associated with destruction of the related renal pyramid. It differs from the scar due to infarction in that with the latter the associated pyramid remains, albeit reduced in size (Smith, 1962). It is thus easily recognized in excretion pyelography when this procedure is conducted so that the renal outlines are defined (either by careful preliminary preparation of the abdomen or by means of tomography). The scar reveals itself as a localized narrowing of the renal substance, often only a few millimetres thick, which is associated with distortion, blunting, or complete absence of the adjacent pyramid, depending on its size and age. There may or may not be a flattening or depres sion in the renal outline at the site (Hodson, 1959). In fact, in many cases the renal outline is remarkably smooth. This appearance can be exactly mimicked by chronic ulcerating tuberculosis, by back-pressure atrophy behind a calculus jammed in a calix, and by what has become known as the phenacetin kidney, except that in the last instance necrotizing papillitis results in the frequent sloughing and separation of the pyramid, which has not yet been seen in our series of pyelonephritic scars. When generalized throughout the kidney such scarring is often confused with generalized back-pressure atrophy due to prolonged obstruction of urine-flow at the renal pelvis or in the ureter. This also presents as a flattening or recession of the actual pyramids associated with narrowing of the renal sub stance, but without scarring. Also, these effects are present uniformly and to an equal degree throughout and produce a radiological appearance which is quite different from the very irregular result of renal scarring. The two can be clearly differentiated, except sometimes in the very small contracted kidney. In fact, experience over 10 years, often checked by surgical and necropsy evidence, has shown that radiology pro vides a very reliable means of diagnosing this scarred form of chronic pyelonephritis during life, and thus a means of studying the life-history of this condition in a manner not possible by other methods of observation. It must be emphasized that often a scar can be so extensive that it must represent the gross destruction of a tissue mass amounting at times to most of an upper or lower renal pole.