Medullary Sponge Kidney

Medullary sponge kidney is not a new clinical and pathologic entity. It has been described by European authors since 1939 (12) but only recently has it received attention in the English literature. It has also been called cystic disease of the renal pyramids (15, 21), multiple cysts of the renal medulla (10), cystic dilatation of the renal collecting tubules (22), renal tubular ectasia (19), and simply sponge kidney (3, 5, 17, 20). Lenarduzzi in 1939 (12) first used the term medullary sponge kidney, likening the appearance of the medulla to a sponge. Description The pathologic changes are confined to the medullary portions of the kidney and consist of dilatation of the collecting tubules of the pyramids associated with multiple small cysts and cyst-like cavities. Some of these cystic structures have been shown to communicate with the ectatic tubules, and the dilated, sometimes branched collecting tubules and small cystic structures frequently contain small calculi. More commonly, both kidneys are involved, but the lesion may be limited to a single pyramid. The changes in the kidney vary greatly, with seemingly normal pyramids adjacent to pyramids that are grossly involved, enlarged, and with flattened and shallow but otherwise normal minor calyces. If the lesion is generalized, the kidney may be enlarged, but the cortex, calyces, pelvis, and ureter are not unusual unless affected by the complications of the disease, namely, repeated infections, stone formation, and passage of stones. Etiology The cause of medullary sponge kidney is unknown; most authors agree that it represents a developmental defect in the formation of the renal collecting tubules. Fleischner (8) described the disease as a heredofamilial one, and its occurrence in siblings has been reported (4). Two brothers with the disease are currently being studied at this hospital. Incidence The condition is uncommon. In 1960 Abeshouse and Abeshouse (1) were able to collect 131 cases from the literature and added 5 of their own. The largest single series to date (44 cases) was reported by Ekström et al., in their comprehensive monograph on the subject (7). In the sixteen-month period from July 1959 through October 1960, 29 instances of medullary sponge kidney were seen at the University of California Medical Center. Fourteen of these were found in the course of intravenous urography, an overall incidence of approximately 0.5 per cent of 2,465 consecutive urograms. Of the remaining 15 patients, 11 were examined at other hospitals and the urograms were seen in consultation, and 4 were patients investigated at this hospital prior to the sixteen-month study period.