A kidney stone,also known as a renal calculus is a solid concretion or crystal aggregation formed in the kidneys from dietary minerals in the urine. Urinary stones are typically classified by their location in the kidney (nephrolithiasis),ureter (ureterolithiasis),or bladder (cystolithiasis),or by their chemical composition (calcium-containing,struvite,uric acid,or other compounds). Kidney stones typically leave the body by passage in the urine stream,and many stones are formed and passed without causing symptoms. If stones grow to sufficient size they can cause obstruction of the ureter. Ureteral obstruction causes postrenal azotemia and hydronephrosis (distension and dilation of the renal pelvis and calyces),as well as spasm of the ureter |