Introduction

Did you know that 1 in 11 people in the U.S. suffer from the excruciating pain of urolithiasis, or kidney stones? This condition not only causes immense discomfort to those affected but also places a significant burden on our emergency departments, with nearly a million visits each year. While many cases resolve themselves through the spontaneous passage of the stones, others present as emergencies requiring procedural interventions. Let’s delve into what makes kidney stones such a daunting challenge for both individuals and healthcare systems.

Classifications

Urolithiasis is categorized based on its location within the urinary tract and its chemical composition, with each aspect significantly influencing management strategies. The etiology varies across different types of stone compositions, leading to distinct preventive measures for each.

Most stones are mixed composition with more than half contain calcium salts.

Epidemiology

The incidence of urolithiasis peaks in young adults aged 20-40 years, with a rate of about 1-2 per 1000 individuals.

The most common type, calcium stones, are found more frequently in men, with a male-to-female ratio of 3:1.

Conversely, struvite and matrix stones are more commonly seen in women, with a male-to-female ratio of 1:2.5.

Etiology

Risk factors

In the prevention section, we will discuss strategies involving the mitigation of risk factors.

Pathogenesis

Stones formation

There are two theories that describe the growth and aggregation of crystal.

1. Fix particle mechanism (Anderson-Carr-Randall theory)
2. Free particle mechanism

1. Fix particle mechanism

The fixed particle mechanism states that stones formed attached to calcific plaques called Randall plaques. These plaques can be visualized as a thin (<2 mm) calcified plaques at renal papillae on CT imaging.

2. Free particle mechanism

Across both fixed and free mechanisms, the formation of microaggregate crystals is proposed to occur through three distinct processes.

• Nucleation
  Crystal/foreign body initiates formation in urine supersaturated with crystallizing salt
• Stone matrix
  Organic matrix of urinary proteins + serum serves as framework for deposition of crystals
• Inhibitor
  Little/no concentration of urinary stone inhibitors such as
  • Citrate
  • Pyrophosphate
  • Glycosaminoglycan
  • Nephrocalcin
  • Tamm-Horsfall protein

Mechanism of renal colic

Clinical manifestation

Regardless of the stone type, patients may exhibit a range of symptoms, from being asymptomatic to critically ill.

Factors that affect clinical findings include the site/degree of obstruction and stone size.

Site of urolithiasis

Associated symptoms

Due to prostaglandin release, there may be associated symptoms such as;

• nausea
• vomiting
• fever

Complication

In cases of severe and/or prolonged urinary obstruction. There may be;

• (Post-renal) acute renal failure
• Oliguria/anuria
• Urinary tract infection
• Sepsis

Laboratory findings

• microscopic hematuria in urinalysis (may be absent in acute total obstruction)
• ↑ serum Cr (due to obstructive uropathy)

Choice of imaging modality

Ultrasound KUB

Plain film KUB

CT for urinary stones

MRI for urinary stones

Acute management

Conservative medical therapy

Approximately 86% of stones pass spontaneously within 30-40 days, with success rates dependent on size. Therefore, patients with smaller (< 5-6 mm), uncomplicated stones may be managed conservatively.

Pain control

• NSAIDs
  • Directly counteract prostaglandin release → first-line treatment for pain
  • Can be given as IV or oral
• Opioids
  • Reserved for refractory pain

Nausea and vomiting management

IV antiemetic medications such as

• Ondansetron
• Metroclopramide
• Promethazine

Dehydration management

Considered IV crystalloid in patients with sign of moderate to severe dehydration or persistent vomiting.

Caution: Use of IV hydration does not show to facilitate stone passage.

Medical expulsive therapy (MET)

• Alpha-blockers
  Useful adjunct to facilitate passage of 5-10 mm stones but not beneficial for smaller ones.
  • Doxazosin
  • Tamsulosin

Hospitalization

Hospitalization for close observation may be considered in patients with;

• Intractable pain or vomiting
• Inability to tolerate oral intake
• Pregnancy
• Pediatric age

Urological intervention

Considered urgent/emergent urological intervention in patients with;

• Larger stones (which are unlikely to spontaneously stone passage)
• Acute complication
• Solitary kidney

Intervention methods

Actual intervention plan should be discussed with urologist according to patient’s presentation, medical conditions, and urologist’s comfort and preference.

Flexible ureteroscopy (URS)

• The most common method used
• Direct endoscopic visualization of the urinary tract and retrieval of an obstructing stone
• Good option for lower pole stones between 1.5-2 cm
• Ideal choice of treatment for patients taking anticoagulant/antiplatelet medication

Extracorporeal shockwave lithotripsy (ESWL)

• Used of ultrasound shockwaves from the body surface to fragment the stone into smaller pieces that can be passed into urine
  • May required follow up flexible URS for ureteral stent
• Typically need IV sedation or general anesthesia (but can be performed on an outpatient basis)
• Some stones are resistant to this method
  • Cystine stones
  • Matrix stones
  • ↑HU calcium stones

Percutaneous nephrolithotomy (PCNL)

Preferred in

• Size > 20 mm
• Staghorn calculi
• Kidney and proximal ureter stones
• Chronic kidney disease

Contraindications

• Pregnancy
• Bleeding disorders
• Active urinary tract infections

Emergent decompression

Considered in patients with acute obstruction with signs of urinary tract infection to prevent permanent renal damage and worsening of infection.

• Indwelling ureteral catheter
• Nephrostomy tube

Prevention

Lifestyle modification

Oral hydration

Oral hydration is recommended at a rate that produces approximately 2.5-3.5 L of urine per day.

Acceptable choice of fluid included

• Water
• Coffee
• Tea
• Beer
• Low sugar fruit juices
  except for
  • Tomato (↑Na content)
  • Grapefruit (↑Oxalate content)
  • Cranberry (↑Oxalate content)

Diet modification

Avoid intake of;

• High oxalate foods⁽¹⁾
• Fish oil
• Vitamin C

Increase intake of;

• Citric acid⁽²⁾
• Calcium⁽³⁾

Specific stones prevention

Calcium stones

• Medications
  • Thiazide diuretics
  • Citrate salts (K citrate)
• Lifestyle modifications

Uric acid stones

• Medications
  • Citrate salts (K citrate)
  • Uric acid lowering medication
    • Allopurinol
• Lifestyle modifications

Cystine stones

• Medications
  • Citrate salts (K citrate)
  • Thiol drugs
• Lifestyle modifications

Differential diagnosis

Footnotes

Further reading

• Urolithiasis
• Kidney and Ureteral Stones