DMSA Case 6 Answers

1) What is the diagnosis?

Horseshoe kidney. The key to the diagnosis here is the abnormal axis of the kidneys - the lower poles point medially.

2) How common is this condition?

The incidence is 1 in 400 with a 2:1 male: female ratio. It is the most common fusional abnormality, characterized by fused lower renal poles. It is variable in appearance and may be asymmetric. The fused portion of the kidney (or "isthmus") may be fibrous or full-thickness normal functioning parenchyma

This is compared to the much rarer Cake/Lump kidney (total fusion) or Disc/Pancake kidney (upper and lower pole fusion). It should also be distinguished from cross-fused ectopia.

3) Name some complications of this condition?

Many horseshoe kidneys are asymptomatic and found incidentally. There may be other anomalies of the genito-urinary tract in up to 50% of patients along with anorectal, cardiovascular and skeletal anomalies. It is seen in 7% of those with Turner’s syndrome and particularly associated with trisomy 18.

This isthmus lies directly anterior to the aorta and prevents normal rotation and migration. Therefore, the pelvises are more anterior and the isthmus gets "caught" on the IMA or less frequently the SMA. The affected kidney characteristically has multiple renal arteries from multiple sources.

The main problems stem from the abnormal path of the ureters. They emerge antero-medially and pass anterior to the isthmus where they are prone to obstruction. Resultant urinary stasis makes the kidney prone to infection and stones. There is a 3-4X increased rate of transitional cell carcinoma, which probably related to chronic infection and stones.

Other problems relate to the isthmus. Wilm’s tumour is 4X more likely to arise from this occasionally dysplastic tissue in childhood and there is reckoned to be an increased risk of renal cell carcinoma later in life. The isthmus is also prone to trauma and may obstruct labour in pregnancy.

Click here to see another case, this time on bone scintigraphy

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The text is entirely the opinion of the author and does not necessarily reflect that of RUH NHS Trust or the Bristol Radiology Training Scheme. Website content devised by Paul McCoubrie.