What is a pancake kidney on CT and ultrasound?
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Answer:
A pancake kidney is a rare fusion anomaly in which both renal masses fail to ascend and fuse completely in the pelvis, forming a single discoid or lobulated mass with no intervening septum and no recognisable separate kidneys. Two distinguishing features separate it from its relatives: unlike a horseshoe kidney, which fuses only at the lower poles and remains in a near-normal position on either side of the spine, the pancake kidney is completely fused and pelvic; and unlike crossed fused ectopia, in which both renal masses lie on one side and one ureter crosses the midline, the pancake kidney’s two ureters remain short and do not cross. The renal pelves face anteriorly and the blood supply is multiple and anomalous, arising from the distal aorta and the common or internal iliac vessels. Complications are recurrent infection, calculi and hydronephrosis from ureteric kinking, and there is a reported increase in malignancy. CT defines the vascular anatomy and is essential before pelvic surgery.
Why is it called so?
The fused kidneys form a single flat, rounded discoid mass in the pelvis, like a pancake.
Pathophysiology
Between the fourth and eighth weeks of gestation the metanephric blastemas normally ascend from the pelvis to the lumbar region while rotating medially. If the two masses lie in contact before ascent, the abnormally close nephrogenic tissue fuses across the midline. The resulting single mass cannot pass between the umbilical arteries and remains in the pelvis, so it never rotates and its pelves stay anteriorly directed. Because the kidney never ascends, it also never acquires a definitive renal artery from the lumbar aorta and retains the primitive segmental supply from whatever vessels lie adjacent, which is why the arterial anatomy is multiple and unpredictable.
Alternative names: Discoid kidney, cake kidney, lump kidney, fused pelvic kidney
Other associated named signs: Horseshoe kidney and its flower vase appearance, crossed fused ectopia, and the drooping lily sign
References
Access all radiology signs posted so far: https://radiogyan.com/radiology-signs/
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