Definition
Renal or urinary calculi are concretions formed by precipitation of various urinary solutes in the urinary tract. They contain calcium oxalate (60%), phosphate as a mixture of calcium, ammonium and magnesium phosphate – also called struvite – (triple phosphate stones are infective in origin) (30%), uric acid (5%) and cystine (1%).
Key Points
- Calculi may develop because of or cause UTIs.
- Most stones (80–85%) pass without complication.
- Most stones are managed non-surgically.
- The pain of renal/ureteric calculi is very severe.
- Ureteric stone with obstruction and upper UTI is a urological emergency requiring immediate IV antibiotics and relief of the obstruction by ureteric stent or nephrostomy.
- Beware of the diagnosis of ureteric colic in patients >60 years – it might be a leaking AAA.
Epidemiology
Male : female 3:1. Early adult life. Among Europeans prevalence is 3%.
Pathogenesis
- Hypercalciuria: 65% of patients have idiopathic hypercalciuria.
- Nucleation theory: a crystal or foreign body acts as a nucleus for crystallization of supersaturated urine.
- Stone matrix theory: a protein matrix secreted by renal tubular cells acts as a scaffold for crystallization of supersaturated urine.
- Reduced inhibition theory: reduced urinary levels of naturally occurring inhibitors of crystallization.
- Dehydration.
- Infection: staghorn triple phosphate calculi are formed by the action of urease-producing organisms (Proteus, Klebsiella), which produce ammonia and render the urine alkaline.
- Schistosomiasis predisposes to bladder calculi (and cancer).
Pathology
- Staghorn calculi are large, fill the renal pelvis and calices, and lead to recurring pyelonephritis and renal parenchymal damage.
- Other stones are smaller, ranging in size from a few millimetres to 1–2 cm. They cause problems by obstructing the urinary tract, usually the ureter. Calyceal stones may cause haematuria and bladder stones may cause infection. Chronic bladder stones predispose to squamous carcinoma of the bladder (rare).
Clinical Features
- Calyceal stones may be asymptomatic.
- Staghorn calculi present with loin pain and upper UTI.
- Ureteric colic – severe colicky pain radiating from the loin to the groin and into the testes or labia associated with gross or microscopic haematuria.
- Bladder calculi present with sudden interruption of urinary stream, perineal pain and pain at the tip of the penis.
Investigations
- FBC, U+E, serum creatinine, calcium, phosphate, urate, proteins and alkaline phosphatase.
- Urine microscopy for haematuria (present in most patients with urinary calculi) and crystals.
- Urine culture: secondary infection.
- Urine pH: <5.0 suggests uric acid stones, >7.0 suggests urea splitting organisms.
- Kidney, ureter, bladder (KUB) radiograph: 90% of renal calculi are radio-opaque.
- CT scanning: non-contrast helical CT scanning is more accurate than IVU in detecting urinary tract calculi. Gives no information about degree of obstruction or renal function.
- IVU: confirms the presence and the position of the stone in the genitourinary tract.
- An ultrasound may be indicated to exclude AAA. May show hydronephrosis or hydroureter if obstruction present.
- A renogram: may be indicated with staghorn calculi to assess renal function.
- 24-hour urine collection when patient is at home in normal environment.
- Stone analysis: origin.
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