Ureteral and Kidney Stones

Etiology

Renal calculi are typically caused by crystallization of supersaturated stone-forming materials in the urine. Calcium, in the form of calcium oxalate, calcium phosphate, and calcium urate, is the most common stone-forming material. Uric acid is the second most common component. Other less common components include xanthine, cystine, struvite, and precipitation of medications such as the protease inhibitor indinavir sulfate in persons infected with human immunodeficiency virus (HIV). Alternatively, renal pathologic processes may initiate crystal formations within the renal tubules that are extruded into the renal collecting system to undergo further growth. Urinary stasis secondary to chronic obstruction or reflux, urinary pH abnormalities, and chronic infections also may contribute to stone formation.

Prevalence and Epidemiology

Nephrolithiasis and ureterolithiasis represent a significant cause of urinary obstruction and abdominal pain. Infections, such as pyelonephritis, pyonephrosis, or renal abscess, may complicate stone disease and may be difficult to differentiate clinically. Imaging evaluation is necessary to confirm the diagnosis of stone disease and detect complications.

The lifetime risk for forming renal stones differs in various parts of the world: it is 1% to 5% in Asia, 5% to 9% in Europe, and 13% in North America. The composition of stones and their location in the urinary tract, bladder, or kidneys also may significantly differ in different countries. Renal stone disease is slightly more common in males than in females and in whites than in blacks. Stones in the upper urinary tract are related to lifestyle and are more frequent among affluent people, those living in developed countries, and in those with diets high in animal protein. A high frequency of stone formation occurs among hypertensive patients and among those with a high body mass index.

Clinical Presentation

Nephrolithiasis and ureterolithiasis often present as severe colicky pain in the region of the flanks that may radiate into the groin. Nausea and vomiting, costovertebral angle tenderness, and hematuria are commonly present with obstruction of a ureter with urinary calculi.

Pathophysiology

Most patients with symptomatic renal or ureteral stones present because of flank pain caused by acute ureteral obstruction. The most common location of the stone is in one of the three areas of narrowing in the ureter: the ureteropelvic junction, the pelvic brim as the ureter crosses into the pelvis, and the ureterovesical junction.

Imaging