Whose side are you on? The diagnostic conundrum of solitary crossed renal ectopia.

A 56-year-old man presents with haematuria and through extensive investigation is found to have solitary crossed renal ectopia. This congenital abnormality occurs as a result of a combination of unilateral renal agenesis and renal ectopia. With only 34 cases reported in the worldwide literature, the rarity of solitary crossed renal ectopia makes its diagnosis a challenge. We review the embryological theories behind this congenital anomaly and highlight some of the typical features demonstrated in our case that would lead one to consider a diagnosis of solitary crossed renal ectopia. We also describe features which have not previously been noted in case reports.