McDonald and McClellan's classification of crossed renal ectopias

Last revised by Daniel J Bell on 3 Feb 2019

McDonald and McClellan classified crossed renal ectopia into four types 1:

  1. bilateral crossed renal ectopia without fusion
  2. unilateral crossed renal ectopia
  3. bilaterally crossed renal ectopia: represents 90% of all crossed ectopias and includes crossed fused renal ectopia  
  4. 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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