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CROSSED FUSED RENAL
ECTOPIA |
Crossed fused renal ectopia is the fusion of both kidneys, with at least one kidney on the side opposite its normal location.
- Incidence = 1/7000 births (1).
- Thought to result from aberrant metanephros development in which the normal displacement of the fetal kidneys from the pelvis to the lumbar fossae is altered or inhibited.
- M > F
- Right (67%)
ETIOLOGY / PATHOPHYSIOLOGY |
Due to abnormal ascent of the kidneys, resulting in abnormalities in renal position, rotation and fusion. Renal ectopic by definition refers to abnormal position of the kidneys. The most common site of an ectopic kidney is in the pelvis, rarely it can be too high and in the chest - a thoracic kidney.
When an ectopic kidney crosses over to the contralateral side it is called crossed renal ectopia and the kidney lies below the contralateral kidney. There is usually fusion between the 2 kidneys and in doing this the crossed lower kidney malrotates so the pelves point to the midline and the crossed kidney's drainage is to the side it would drain to if it had not malrotated.
ULTRASOUND |
- Unilateral empty renal fossa (simulating unilateral renal agenesis however the other kidney is large and bilobed).
- Single larger than normal kidney (size alone should not be used to differentiate a renal agenesis from a crossed fused renal ectopia).
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Renal
length – 6 cm |
- Two echogenic collecting systems.
- Contour of the kidney.
- In unilateral renal agenesis the kidney is enlarged but normal.
- In crossed fused ectopia the kidney is composed of two smaller kidneys joined and often separated by a notch (bilobed).
- Color doppler of the renal arteries may assist.
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- Fifty percent of patients have associated genitourinary, skeletal and cardiac valvular defects.
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CT Scan or croosed
fused renal ectopia on right
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Note the anterior rotation of
the renal pelvis due to the associated malrotation
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REFERENCES |
- Greenblatt AM, Beretsky I, Lankin DH et.al. In utero diagnosis of crossed renal ectopia using high resolution real time ultrasound. J Ultrasound Med 1985;4:105.
- Jeanty P, Romero R, Kepple D et.al. Prenatal diagnosis of unilateral empty renal fossa. J Ultrasound Med 1990;9:651-654.