McDonald and McClellan classified crossed renal ectopia into four types 1:
- bilateral crossed renal ectopia without fusion
- unilateral crossed renal ectopia
- bilaterally crossed renal ectopia: represents 90% of all crossed ectopias and includes crossed fused renal ectopia
- crossed unfused renal ectopia
They also described six forms of crossed fused renal ectopia in decreasing order of frequency 1:
- type a: inferior crossed fusion, the upper pole of the ectopic kidney fuses with the lower pole of the normal kidney
- type b: sigmoid or S-shaped kidney, the hilum of the ectopic kidney faces laterally and that of the normal kidney faces medially
- type c: lump kidney, both kidneys fuse over a wide margin with the ureter of the ectopic kidney crossing midline
- type d: L-shaped kidney, a.k.a. tandem kidney, in which the ectopic kidney is horizontally oriented and fused with the lower pole of the normal kidney
- type e: disc/pancake kidney, with extensive fusion of both kidneys forming a disc-shaped mass
- type f: superiorly crossed fused, the ectopic kidney is placed above the normal kidney and fused with its upper pole
History and etymology
James H McDonald and Don S McClellan, American urologists, published their classification in 1957 1.
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