Pathophysiology and Management of Renal Calculi

Calcium Stones (75%)

Calcium stones are the most common type, accounting for approximately 75% of all cases. They typically form when excess calcium combines with either oxalate or phosphate. This type of stone is most frequently seen in middle-aged men and often presents with a positive family history.

Struvite Stones (15%)

Struvite stones are composed of magnesium and ammonium phosphate. These are frequently associated with microbial infections in women, specifically involving bacteria such as Proteus or Pseudomonas. These bacteria possess the ability to split urea into ammonia, which alters the urinary environment to favor stone formation.

Uric Acid Stones (10%)

Uric acid stones form in highly acidic urine. This acidity is often the result of underlying medical conditions, such as:

• Gout
• Leukemia
• Ulcerative colitis

Cysteinuria (2.5%)

Cysteinuria is a rare hereditary condition characterized by the decreased reabsorption of the amino acid cysteine. This leads to high levels of cysteine in the urine, which eventually crystallizes into stones.

Exam Tip: When reviewing urinalysis, remember that the presence of crystals (such as uric acid or calcium oxalate) is a key indicator of stone-forming potential.

Clinical Presentation and Symptoms

The clinical course of renal calculi can vary. Many patients may remain asymptomatic until the stone begins to move or causes an obstruction. Common symptoms include:

• Renal Colic: Intense, spasmodic pain often felt in the flank.
• Haematuria: The presence of blood in the urine.
• Gastrointestinal Distress: Nausea and vomiting.
• Urinary Changes: Increased urgency and frequency of urination.
• Systemic Signs: Fever, which may indicate an associated infection.

Management and Treatment

The management of renal calculi depends on the size of the stone and the severity of the symptoms.

Conservative Management

In many cases, more than 90% of stones will pass naturally through the urine within a period of 3 to 6 weeks. During this time, pain relief is a primary clinical priority.

Surgical and Interventional Options

If stones are too large to pass or cause significant obstruction, medical intervention is required:

• Extracorporeal Shock Wave Lithotripsy (ESWL): A non-invasive procedure that uses shock waves to break stones into smaller fragments that can then be passed.
• Surgery: Direct surgical removal of the stones.
• Short-term interventions: In cases of obstructive uropathy, doctors may use stents, nephrostomy, or catheters to manage urine flow.

If both kidneys sustain significant damage due to prolonged obstruction, long-term treatments such as dialysis or a kidney transplant may become necessary.