Definition of Renal Calculi
Renal calculi are mineral deposits that form in the renal calyces and pelvis of the kidney, either free-floating or attached to the renal papillae, composed of crystalline and organic components that develop when urine becomes supersaturated with specific minerals. 1
Basic Composition and Formation
- Calcium oxalate is the most common constituent, found in the majority of kidney stones 1
- Many calcium stones form on a foundation of calcium phosphate called Randall's plaques, which are present on the renal papillary surface 1
- Stones contain both crystalline minerals and organic components that bind together when urine supersaturation occurs 1, 2
Common Stone Types
Calcium-Based Stones
- Calcium oxalate stones are the predominant type and rarely grow in staghorn configuration 3
- Calcium phosphate stones also rarely develop into staghorn calculi 3
- Stones from certain metabolic conditions may contain mixtures of calcium oxalate and calcium phosphate 3
Struvite (Infection) Stones
- Composed of magnesium ammonium phosphate (struvite) and/or calcium carbonate apatite, these are strongly associated with urinary tract infections from urease-producing bacteria 4, 5
- Bacteria reside within the stone itself, making the stone infected (unlike other stone types where stones remain sterile inside) 4, 5
- Most frequently form staghorn calculi, which are branched stones that fill the renal pelvis and extend into multiple calices 4
Other Stone Types
- Uric acid stones are radiolucent on plain radiography and can grow in staghorn configuration 3
- Cystine stones can also form staghorn configurations and are commonly resistant to shock wave lithotripsy 3
Clinical Significance
Prevalence and Risk
- Stone disease affects up to 14.8% of the population with increasing rates 1
- Recurrence rate reaches up to 50% within 5 years of the initial stone episode 1, 2
- Obesity, diabetes, hypertension, and metabolic syndrome are established risk factors 1
Complications
- Untreated staghorn calculi can destroy the kidney and cause life-threatening sepsis 4, 5
- Stone disease can lead to hypertension, chronic kidney disease, and end-stage renal disease 1
- Calcium oxalate precipitation may cause discrete stones or diffuse nephrocalcinosis leading to chronic renal failure 4
Important Clinical Distinctions
- Stone composition directly determines treatment approach, as different types respond differently to lithotripsy and require specific medical management strategies 3
- Stone analysis should be obtained at least once when a stone is available to guide preventive measures 4
- Complete stone removal is particularly critical for struvite stones to eradicate causative organisms, relieve obstruction, and preserve kidney function 4, 5