Result from crystal formation in urine: increased concentration of solute (Calcium, oxalate, cysteine, urate, xanthine), reduced volume of urine or low levels of inhibitors of stone formation (Citrate, Mg, nephrocalcin).
Epitaxy – Urinary calculi have a mixture of crystals amoungst which one predominates. A foreign body (catheter, organic matrix of proteins (Tamhorsfall), another stone, necrotic renal papilla, schistosome ova) forms a nucleus around which stone forms.
Calcium stones (70%) are either calcium oxalate (40%) or calcium phosphate (15%) or mixed (Calcium oxalate-phosphate).
— Increased calcium in urine. Can be associated with normal serum calcium (absorptive hypercalciuria, tubular calium leak) or hypercalcaemia.
— Increased uric acid in urine may encourage formation of calcium stones.
— Increase urinary oxalate (inherited or acquired – from increased intake, fat malabsorption or excessive Vit C)
— Reduced urinary citrate
Uric acid stone (8%). Radiolucent. Acid urine. Can occur in hyperuricaemic patients or patients with normal serum Urate.
Struvite stone (Magnesium ammonium phosphate and carbonate apetite) 15%. Urease splitting UTI with proteus, klebsiella or mycoplasma. Staghorn calculus. Alkaline urine
Cysteine stones (2%). Very hard stones forming in acid urine. Due to congenital disorder of cyteine resportion.
Loin, unbilicus, testis
— Mid ureter
— Lower ureter
Scrotum, tip of penis / labia
± bladder irritability
For all first time stone formers
· MSU, microscopy for RBC, WBC, casts, cyrstals
— U&E, Ca++, uric acid, PO4-
· Retrieve and analyse stone
· Spot urinary cysteine test
— Gold standard
— Non-contrast enhanced spiral CT
— Thick slices
— Aim to visualise stone
For patients with recurrent stones, multiple stones, nephrocalciuosis perform 2 24 hour urine collections for calclium, oxalate, urate, phosphorous, citrate, creatinine, volume and pH.
v Obstruction + infection® urgent decompression with percutanous nephrostomy
Size and probability of spontaneous resolution
— 4mm – 90%
— 4 – 6mm: 40%
— >6mm: 25%
— Absolute indications for intervention: obstruction and sepsis, obstruction and deteriorating renal function
— Relative indication: stone >6mm, continuing pain, failure to resolve after adequate period of observation
Interventions for renal stone
— ESWL: Stones <2cm (less than 1cm in lower pole calyx).
o Absolute contra-indication: AAA, Pregnancy, obstruction
o Relative contra-indication : obesity, cystein stones, horseshoe kidney, solitary kidney.
o Complications: infection, stein strasse obstruction, pain, bruising, intra-renal haematuria.
— PCNL: Stones >2cm. Stone fragmented with US, pneumatic or electrohydrolic device.
— Open surgery: Removal of stone either through renal sinus (Gil-Vernet) or nephrotomy. Nephrectomy is used when kidney contributes <15% of renal function and is infected
Interventions for ureteric stones
— Ureteric stent: can be used to relieve obstruction when associated with infection or deteriorating renal function. Prophylactic before ESWL for renal stones, Push-bang to displace mid-ureteic stones proximally for ESWL.
— ESWL: Least successful for mid-ureteric stones (65%) compared to lower and upper 1/3 stones (80%).
— Ureteroscopy. Can use flexible (laser only) or rigid (laser, pneumatic device or US for fragmentation). Most successful for upper 1/3 (96%) vs middle 1/3 (75%) vs lower 1/3 (55%).
— Dormia basket can be used only with stones 5mm in size no more than 5cm from ureteric orifice
o All ureteric procedures can be complicated by ureteric perforation, avulsion or late stricture.
· 2 x fluid intake
· Metabolic evaluation
— Stone analysis
— 24hr urine
calcium, uric acid, oxalate, citrate, sodium, volume, pH
Urea, creatinine, calcium, phosphate, uric acid