The pancake kidney, also known as a cake, doughnut, disc, shield, or lump kidney, describes the least common congenital renal fusion anomaly, where the kidneys are completely fused as a lobulated mass in the pelvis (Fig. 1A, B), resembling a pancake (Fig. 2) [1, 2]. The fused kidneys retain separate collecting systems, draining into short ureters that insert normally into the urinary bladder. First described by Looney and Dodd [3], the pancake kidney is considerably rarer than its partially fused cousin the horseshoe kidney, with an estimated incidence of 1 in 65,000-375,000 [2]. It has been postulated that this anomaly arises during development when the umbilical arteries press the nephrogenic primordia together, causing them to fuse and fail to ascend from the pelvis [4]. Vascular supply can be anomalous in both number and origin, arising from the distal aorta or iliac arteries [2]. The collecting systems are also abnormally rotated to face anteriorly [4], and are associated with various duplex configurations [2]. Often an incidental finding, asymptomatic patients can be managed conservatively with monitoring of renal function [1, 4]. Surgery can be considered if complications such as urinary tract infection, stone formation, or obstruction occur [5].
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