[The nucleus of ossification in kidney calculus]

The presence of bone tissue in renal stones has been described for a long time. Two cases of heterotopic ossification are reported in this study. Stone analysis was performed by stereoscopic microscopy, infrared spectrophotometry and fine slice petrographic section and polarized light microscopy. This last technique revealed the existence of osteocytic filling defects inside the stones, an unquestionable sign of mineralized bone tissue.