The residual renal stone.

A study of the observer error built in to contact preoperative radiography for renal stones shows that particles less than 2 mm in diameter are likely to be missed. The radiographic follow-up of 100 patients from whom 120 large staghorn calculi have been removed over a period of up to 10 years shows that new calculi may form in kidneys which have been completely cleared, and that residual stones do not always grow, but equally often pass spontaneously, or remain unchanged.