Nephrolithiasis

Last updated: April 11, 2022

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Nephrolithiasis encompasses the formation of all types of urinary calculi in the kidney, which may be deposited along the entire urogenital tract, from the renal pelvis to the urethra. Risk factors include low fluid intake and high-sodium, high-purine, 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 composed 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, commonly called renal or ureteric colic, and it is usually associated with hematuria. Diagnostics include spiral CT without contrast and/or ultrasound of the abdomen and pelvis to detect the stone, as well as urinalysis to assess for concomitant urinary tract infection (UTI) and serum BUN and creatinine to evaluate kidney function. Small stones that do not require urgent urological intervention can be managed with symptomatic treatment and a trial of medical expulsive therapy to promote spontaneous passage. If spontaneous passage appears unlikely or fails because of the size or location of the stone, first-line urological interventions include shock wave lithotripsy, ureterorenoscopy, and, in patients with large kidney stones, percutaneous nephrolithotomy. The most important preventive measure is adequate hydration. In addition, the analysis of passed stones may provide information to guide dietary changes and/or medical therapy (e.g., thiazide diuretics, urine alkalinization) that can prevent future stone formation.

Epidemiological data refers to the US, unless otherwise specified.

Overview of kidney stones

Types Incidence Etiology/associated findings Urine pH
Crystal appearance Radiopacity Prophylaxis

Calcium oxalate stones

  • 75%
  • ↓ Urine pH (acidic)
  • Biconcave dumbbells or bipyramidal envelopes
Uric acid stones
  • ∼ 10%
  • ↓ Urine pH (acidic) and volume (often seen in desert climates)
  • Rounded rhomboids, rosettes, or needle-shaped
Struvite stones
  • ∼ 5–10%
  • ↑ Urine pH (alkalic)
  • Rectangular prisms (coffin lid-appearance)

Calcium phosphate stones

  • < 5%
  • ↑ Urine pH (alkalic)
  • Wedge-shaped prisms
Cystine stones
  • ↓ Urine pH (acidic)
  • Hexagon-shaped
Xanthine stones
  • Xanthinuria (hereditary)
  • Generally independent of urine pH
  • Amorphous
  • N/A

Calcium oxalate stones [2]

Crohn disease leads to increased oxalate absorption via malabsorption of fatty acids, which can ultimately cause nephrolithiasis.

Uric acid stones

Uricosuric agents (e.g., probenecid) increase the excretion of uric acid, which can accelerate the formation of stones.

Uric acid stones are radiolUcent (x-ray negative).

Struvite stones (magnesium ammonium phosphate stones)

Urinary tract infections can lead to the formation of struvite stones, but struvite stones also increase the risk of urinary tract infections.

Calcium phosphate stones [2]

Cystine stones [8]

To remember that cystine crystals are hexagonal, think “The Cystine Chapel has six sides.”

Xanthine stones

2,8-Dihydroxyadenine stones

Ammonium urate stones

Drug-induced stones

Can be caused by:

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. [10]

  • Severe unilateral and colicky flank pain (renal colic) ; [11]
  • Hematuria
  • Nausea, vomiting, and reduced bowel sounds
  • Dysuria, frequency, and urgency
  • Passage of gravel or a stone
  • Patients are usually unable to sit still and move around frequently (opposed to patients with peritonitis, who usually prefer to lie still)

Depending on the location of the stone, nephrolithiasis may resemble conditions such as appendicitis or testicular torsion.

Approach [13][14][15]

Laboratory studies [13][14]

Laboratory studies are not necessary for the diagnosis of nephrolithiasis, but they may help narrow the differential diagnosis and identify complicating factors (e.g., acute kidney injury, UTI).

Urinalysis [14][16]

Imaging studies [20][21][22]

  • Recommendations in this section are consistent with the 2015 American College of Radiology (ACR) appropriateness criteria for acute-onset flank pain with suspicion of stone disease. [20]
  • In general, an initial presentation suspicious for nephrolithiasis requires confirmatory CT imaging.
  • Imaging is also indicated for acute flank pain of uncertain etiology, e.g., to rule out AAA.
  • Routine CT is controversial in young patients with uncomplicated presentations of renal colic , especially those with a history of nephrolithiasis. [20][23][24][25]

CT abdomen and pelvis without contrast and ultrasound of the abdomen and pelvis are the preferred diagnostic tests for nephrolithiasis in patients for whom imaging is indicated.

CT abdomen and pelvis without IV contrast

CT has the highest accuracy of the imaging modalities to identify kidney stones.

  • Type: low-dose, helical (spiral) CT without contrast
  • Indication: first-line for nonpregnant patients with suspected nephrolithiasis
  • Findings [20]

Hydronephrosis and/or hydroureter without calculi may suggest a recently passed kidney stone. [20]

The addition of IV contrast may help to differentiate ureteral stones from phleboliths and increases the likelihood of detecting alternative causes of abdominal pain (e.g., appendicitis, diverticulitis). However, IV contrast reduces the sensitivity for kidney stones to ∼ 80% compared to > 95% in CT without contrast. [20]

Ultrasound abdomen and pelvis

  • Indications: suspected nephrolithiasis in patients for whom radiation exposure should be minimized (e.g., pregnant patients, pediatric patients, those with recurrent stones)
  • Findings

X-ray kidney, ureter, and bladder (KUB)

  • Indications: follow-up for previously identified radiopaque stones after the initiation of treatment
  • Findings: radiographic densities (e.g., stones, phleboliths, vascular calcifications)

Because KUB sensitivity is proportional to stone size, it is usually only suitable for larger stones.

MRI abdomen and pelvis with or without IV contrast

  • Indications: suspected nephrolithiasis in patients for whom radiation exposure should be minimized (e.g., pregnant patients or children)
  • Findings: similar to CT

Intravenous pyelogram (IVP)

  • Indications: rarely indicated given the broad availability of CT
  • Findings
    • Provides a complete outline of the urinary tract system
    • Size and location of stone, degree of obstruction

Further evaluation [13][15]

For initial episodes of nephrolithiasis, patients should undergo a limited metabolic evaluation to rule out underlying systemic disorders and guide preventative therapy. This workup is typically unnecessary following repeat visits for renal colic where the underlying etiology is already known.

  • Dietary history: fluid intake, protein, calcium, sodium, fruits, vegetables, high-oxalate foods, over-the-counter supplements
  • Laboratory studies: BMP , calcium , uric acid , urinalysis
  • Stone composition analysis [26]
  • 24-hour urine profile
    • Measures saturation of stone-forming salts and other parameters, such as total volume, pH, and creatinine
    • Dietary changes, medical therapies, or additional testing may be recommended based on the results.

Provide patients with a first-time diagnosis of nephrolithiasis with a urine strainer at the time of discharge to collect passed stones for compositional analysis during their follow-up.

The differential diagnoses listed here are not exhaustive.

Recommendations in this section are consistent with the 2016 American Urological Association (AUA) guideline on the surgical management of kidney stones and the 2019 AUA guideline on the medical management of kidney stones. [13][27]

Approach [21][27]

  • Initiate symptomatic management prior to confirmatory imaging for patients with renal colic.
  • Consult urology urgently for interventional treatment in the following cases:
  • Attempt a trial of conservative management for patients with small (≤ 10 mm), uncomplicated stones.
  • Disposition: Most patients with uncomplicated nephrolithiasis can be treated successfully with conservative management during an emergency department visit of a few hours.
    • Admit patients requiring urgent urology consult and intervention.
    • Ensure outpatient urology follow-up for all patients eligible for discharge (e.g., no indications for urgent urology consult, resolved symptoms, no complications).
  • Tailor recurrence prevention measures to the type of stone; see “Prevention” for details.

The larger the stone, the less likely it is to pass spontaneously.

Obstructing nephrolithiasis with suspected infection requires urgent urology consultation and management. [27]

Symptomatic management [16][21]

Conservative management [21][27]

Interventional management [27]

Overview

The choice of interventional treatment is based on the size and location of the stone, suspected infection, and shared decision-making.

Procedures

Urological interventions for nephrolithiasis [27][29]
Intervention

Description

Indications

Extracorporeal shock wave lithotripsy (ESWL)
  • Acoustic shockwaves used to fragment stones (noninvasive)
  • Stones are localized using fluoroscopy or ultrasound.
  • Ureteral stones
  • Lower renal pole stone ≤ 10 mm
  • All other renal stones ≤ 20 mm

Ureterorenoscopy (URS)

Percutaneous nephrolithotomy (PCNL)
  • Lower renal pole stones > 10 mm
  • All other renal stones > 20 mm

Ureterolithotomy

  • Open, laparoscopic, or robotic surgery (invasive)
  • An incision is made into the ureter and the stone is removed.
  • Rarely indicated
  • Reserved for patients for whom other interventions have been unsuccessful

The need for follow-up imaging after conservative or interventional management depends on the symptoms, stone type, and intervention modality.

We list the most important complications. The selection is not exhaustive.

  • Stone size and location determine the likelihood of spontaneous passage: Stones ≤ 5 mm tend to pass spontaneously, while stones ≥ 10 mm are unlikely to do so, especially if located in the pyelon or proximal ureter. [7]
  • 50% of patients may have a new episode of nephrolithiasis within 10 years. [1]

Low calcium diets increase the risk of calcium-containing stone formation because they increase oxalate reabsorption.

Nephrolithiasis in pregnancy

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