Renal Pyramidal Structure Opacification in Excretory Urography and its Relation to Medullary Sponge Kidney

Medullary sponge kidney is a relatively uncommon disorder characterized by ectasia of the collecting tubules of the pyramids, frequently associated with small cysts or cyst-like structures and minute concretions (1, 4, 7, 8, 10). In a recent review of a series of 2,465 consecutive intravenous urograms 14 cases were discovered, an overall incidence of approximately 0.5 per cent (9). When the lesion is severe and pyramidal concretions are present, the differential diagnosis involves primarily the separation of medullary sponge kidney from diseases causing nephrocalcinosis, particularly renal tubular acidosis and hyperparathyroidism. To a lesser extent, papillary necrosis, unusual renal tuberculosis, and abscesses with chronic pyelonephritis have to be excluded. When the lesions are well developed, the diagnosis of medullary sponge kidney usually presents no problem (3). A mild case, on the other hand, frequently goes unrecognized. The chief diagnostic difficulty in this mild group has been the exclusion of pyramidal opacification, sometimes referred to as “pyramidal blush” or sunburst, flame-shaped, or brush-like opacification of the pyramids (5, 6). Most authorities agree that, in the absence of urinary tract obstruction, opacification of pyramidal structures on excretion urography is not a morbid condition. On the other hand, several authors (2, 6, 11) have regarded this phenomenon as an indication of ectasia of the renal collecting tubules and have speculated upon its relationship to medullary sponge kidney. In the 2,465 intravenous urograms previously mentioned, excluding the cases of medullary sponge kidney, 21 examples of varying degrees of pyramidal blush were found, an incidence of less than 1 per cent. This report presents evidence to support the thesis that the phenomenon of pyramidal blush is a roentgen manifestation of benign dilatation of the collecting tubules. The dilatation varies in degree and, in the instance of more pronounced ectasia and cyst-like changes, results in the symptomatic pathologic entity called medullary sponge kidney. The latter is frequently complicated by the formation of small pyramidal concretions. Material In conjunction with a continuing clinicoradiologic study of medullary sponge kidney at the University of California Medical Center, San Francisco, past and current excretory urograms in which the phenomenon of pyramidal opacification was noted, were re-examined. Only radiographs which showed this opacification in the absence of external abdominal compression, calyceal spasm, or upper urinary tract obstruction were included. Among these were several which had been obtained with one or another of the older contrast media, indicating that the phenomenon is not simply a matter of better opacification by the newer urographic agents.