Is there a correlation between urolithiasis in horseshoe kidneys and isthmus thickness or renal angulation?

Stone disease is a common complication of horseshoe kidneys (HSK). There are currently limited studies that examine the relationship between HSK anatomy and stone formation. We aim to determine if there is such an association by measuring the isthmus size and renal angulation in both stone and non-stone forming HSK using computed tomography (CT).

This is a retrospective study performed at a single tertiary centre. Using the radiological information system, all CT reports between 01 January 2010 and 31 December 2015 were searched for the keyword 'horseshoe' on the radiological information system. This produced a list of 285 reports. Each report and image packet of these 285 studies were reviewed to confirm the presence of an HSK and duplicate patients from multiple examinations were highlighted. One hundred and thirty-eight unique HSK patients were obtained and the studies were assessed for the presence or absence of stones. A total of 112 HSK were found; 88 of which contained no stone and 24 with stone. Angle measurements and isthmus size were measured on these kidneys. As axial images are obtained as standard in all cases, these measurements were all obtained in the axial plane. All parameters were measured and recorded manually by one person so as to reduce inter-observer variability.

Isthmus size varied widely, measuring from 2 to 39 mm. Right renal angle ranged from 51 to 158°, left 38 to 152°.

The isthmus size and renal angle measurements were not found to be significant determinants for stone disease in our patient population.