Rare variations in renal anatomy and blood supply: CT appearances and embryological background. A pictorial essay.

Helical CT angiography is increasingly used for the evaluation of the kidneys and the renal vessels. Knowledge of the potential variants in renal and renal vascular anatomy and of their appearances on helical CT are thus indispensable for radiologists who perform and interpret such examinations. We report six cases of anatomic variants that we encountered in our tertiary referral centre over the past 5 years, during which time we have performed 4850 helical CT angiograms, including 1432 renal artery examinations. These represent rarer anomalies in renal vascularization, most of which were associated with renal malformations (horseshoe kidney with or without cortical torsion, renal malrotation, single kidney, and thoracic origin of a renal artery). We present the helical CT findings and discuss the possible embryological mechanisms and the practical implications of these abnormalities for the radiologist.