What is the approximate incidence of this kind of anomaly?
Horseshoe kidney is one of the most frequently encountered congenital renal anomalies, seen in 1:400-500 individuals, more commonly in males (M:F=2:1).
Apart from its association with urinary tract infections and stones, is it true that this anomaly poses a risk of carcinoma? If yes, which neoplasm?
Horseshoe kidney are associated with transitional cell carcinoma of pelvis, presumably due to stasis, and Wilms tumour.
Is the diagnosis easily made on ultrasound?
Yes and no. If the patient is being scanned supine (rather than prone) and the operator is familiar with the condition, the abnormal orientation of the kidneys and the fusion of the lower poles should be evident. In obese patients, of those with an abundance of bowel gas the lower poles may not be well imaged. Additionally the parenchymal band connecting the lower poles of kidney, seen anterior to aorta, may be mistaken as a retroperitoneal lymph nodal mass.
CT of the abdomen and pelvis demonstrates complete fusion of lower poles of both kidneys. The junction is in the midline, below the inferior mesenteric artery origin. The extra-renal pelvis is prominent on both sides with out frank hydronephrosis.