Abstract
We describe two cases of stones with unusual radiological characteristics in transplanted kidneys that originated from a blood clot as the nidus for lithogenesis. Both patients presented years after renal transplant, with gross haematuria. CT of the urinary tract showed a stone with a peripheral hyperdense shell (Hounsfield unit, HU >500) and a radiolucent centre (HU <100). Both patients underwent percutaneous nephrolithotomy successfully.Stone analysis showed that the outer shell was calcium oxalate monohydrate and further examination of the stone in the second case confirmed an inner layer of organised clot material. Although the management of these clot stones is similar to that of other types of stones, clinicians should be aware of such a phenomenon and investigate the patients for the possibility of stone formation after haematuria, especially in allograft kidneys.