- Clinical science
Nephrolithiasis encompasses the formation of all types of urinary calculi in the kidney, which may deposit along the entire urogenital tract from the renal pelvis to the urethra. Risk factors include low fluid intake, high-sodium, high-purine, and low-potassium diets, which can raise the calcium, uric acid, and oxalate levels in the urine and thereby promote stone formation. Urinary stones are most commonly composed of calcium oxalate. Less common stones are made up of uric acid, struvite (due to infection with urease-producing bacteria), calcium phosphate, or cystine. Nephrolithiasis manifests as sudden onset colicky flank pain that may radiate to the groin, testes, or labia (renal/ureteric colic) and is usually associated with hematuria. Diagnostics include noncontrast spiral CT of the abdomen and pelvis or ultrasound to detect the stone, as well as urinalysis to assess for concomitant urinary tract infection and serum BUN/creatinine to evaluate kidney function. Small uncomplicated stones without concurrent infection or severe dilation of the urinary tract may be managed conservatively with hydration and analgesics to promote spontaneous stone passage. When the spontaneous passage appears unlikely or fails due to the stone's size or location, first-line urological interventions include shock wave lithotripsy, ureterorenoscopy, and, in case of large kidney stones, percutaneous nephrolithotomy. The most important preventive measure is adequate hydration. Collected stones should be sent for chemical analysis because in many cases specific lifestyle guidance, diet changes, and/or initiation of medical treatment (e.g, thiazide diuretics, urine alkalinization) can prevent future stone formation.
|Crystal appearance||Radiopacity||Urine alkalinization||Urine acidification|
|∼ 75%|| || |
Biconcave dumbbells (calcium oxalate monohydrate) or bipyramidal envelopes (calcium oxalate dihydrate)
|Uric acid stones||∼ 10%|| || |
Rounded rhomboids or needle-shaped
|Struvite stones||∼ 5–10%|| || |
Rectangular prisms (coffin lid-appearance)
|Calcium phosphate stones||< 5%||Wedge-shaped prisms||✓✓||-||✓|
|Cystine stones|| |
|Xanthine stones|| ||Amorphous crystals||-||-||-|
- Calcium oxalate monohydrate (“whewellite”): brown or black calculi
- Calcium oxalate dihydrate (“weddellite”): light yellow calculi
- Specific preventive measures
- Persistently acidic urine
- , and hyperuricosuria
- Specific treatment: oral chemolitholysis via
- Specific preventive measures
- Specific preventive measures
Less common stones
- Calcium phosphate stones
- Cystine stones
- 2,8-Dihydroxyandenine stones
- Ammonium urate stones
- Crystallization of drug compounds in the urine: most commonly associated with aciclovir, indinavir, sulfonamides, fluoroquinolones, ceftriaxone
- Stone formation due to alterations in urine composition: most commonly associated with acetazolamide, furosemide, topiramate, vitamin D or vitamin A supplements, Aluminium magnesium hydroxide, calcium supplements
Stones usually form in the collecting ducts of the kidneys but may be deposited along the entire urogenital tract from the renal pelvis to the urethra. Their localization and size determine the specific symptoms. Small kidney stones may also be asymptomatic and detected incidentally.
Severe unilateral and colicky flank pain (renal colic)
- Radiates anteriorly to the lower abdomen, groin, labia, testicles, or perineum
- Paroxysmal or progressively worsening
- The area around the kidneys may be tender on percussion (costovertebral angle tenderness)
- Nausea, vomiting, and reduced bowel sounds
- Dysuria, frequency, and urgency
- Passage of gravel or a stone
Initial diagnostic workup includes imaging studies to locate the stone and laboratory tests to determine kidney function and assess for UTI.
- ↑ WBC: suggests concomitant UTI
- ↑ Serum urea nitrogen and creatinine: suggests acute kidney injury
Urine dipstick and urinalysis
- Gross or microscopic hematuria
- Pyuria, positive leukocyte esterase, positive nitrites, or bacteriuria (suggests UTI)
- Urine pH
- Urine microscopy: may detect crystals
- Urine culture: obtain in patients with clinical or laboratory signs of UTI
- Straining of urine: enables chemical analysis of stone composition and specific guidance on preventive treatment (see prevention section below)
- Metabolic evaluation: indicated in recurrent stones formers and high-risk first-time stone formers
Nonenhanced abdominopelvic CT scan: (gold standard) Demonstrates calculus size, site, density , and degree of obstruction
- Hydronephrosis: dilatation of the urinary tract proximal to the site of obstruction
- May be performed using a low-dose or ultra low-dose nonenhanced CT protocol to minimize radiation exposure with comparable sensitivity and specificity
- Ureteral dilation without stone may indicate recent spontaneous passage
- Post IV contrast: used to demonstrate the functioning renal parenchyma, may demonstrate indinavir stones
- Ultrasound: method of choice for patients in whom radiation exposure should be minimized (e.g., pregnant patients, children, recurrent stone formers) or if a gynecological or abdominal differential diagnosis is likely
- Kidney, ureter, and bladder (KUB) X-ray
- Intravenous pyelogram (IVP)
- Nonenhanced abdominopelvic CT scan: (gold standard) Demonstrates calculus size, site, density , and degree of obstruction
Noncontrast abdominopelvic CT scan or ultrasound are the tests of choice for diagnosis of nephrolithiasis!
- Determine if it is a complicated case, including: high-grade or infected hydronephrosis, urosepsis, acute kidney injury, intractable pain, or vomiting
- Hemodynamically stable patients with uncomplicated stones ≤ 10 mm → a trial of observation with symptomatic treatment to enable spontaneous passage
Urological intervention required for:
- Patients with stones > 10 mm
- Complicated stones
- Paitents who decline conservative treatment
- Failure to pass the stone spontaneously after 4–6 weeks
- For most patients with kidney or ureteral stones ≤ 20 mm, first-line interventional treatments include both ureterorenoscopy and shock wave lithotripsy.
- For patient with kidney stones > 20 mm, percutaneous nephrolithotomy is preferred.
- Uncomplicated stones ≤ 10 mm: offer observation with symptomatic treatment and, especially in case of distal ureteral stones > 5 mm, medical expulsive therapy
- Uric acid stones: dissolve with urine alkalinization
- Ureteral stenting or percutaneous nephrostomy : Surgical decompression in case of severely obstructed or infected pyelon; in those cases, definite stone treatment should be delayed until the infection has resolved.
Extracorporeal shock wave lithotripsy (SWL)
- First-line treatment option for renal stones ≤ 20 mm and ureteral stones
- Lowest complication rate but often repeated SWL is necessary for patients with residual stone burden
- Stones have to be clearly visible on x-ray and/or ultrasound
- Contraindicated in case of untreated UTI, during pregnancy, and in patients with bleeding diathesis; not preferred in morbidly obese patients
- Ureterorenoscopy (URS) ;:
- Percutaneous nephrolithotomy : first-line treatment for renal stones > 20 mm
- Laparoscopic or open stone removal (pyelolithotomy or ureterolithotomy): only considered in rare cases where other interventional methods have previously failed or are likely to do so (e.g., because of complex staghorn stones)
Follow-up imaging is indicated after both conservative and operative treatment to ensure freedom of stones!
- Stone size and location determines likelihood of spontaneous passage: Stones ≤ 0.5 cm tend to pass spontaneously, while stones ≥ 1 cm are unlikely to do so, especially if located in the pyelon or proximal ureter.
- 50% of patients may have a new episode of nephrolithiasis within 10 years.
- Sufficient fluid intake (≥ 2.5 L/day)
- For calcium stones:
- For uric acid stones or high urinary uric acid levels in those with calcium stones: allopurinol
- Depending on urinary pH and stone composition: urine alkalinization or acidification (see specific measures in the classification section)
Low calcium diets increase the risk of calcium-containing stone formation because they increase oxalate reabsorption!