Renal tract calculi

 

Aetiology

 

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

Calcium stones (70%) are either calcium oxalate (40%) or calcium phosphate (15%) or mixed (Calcium oxalate-phosphate).

Causes:

    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.

 

Clinical

· Pain

— Renal

Loin, unbilicus, testis

— Mid ureter

Iliac fossa

— Lower ureter

Scrotum, tip of penis / labia

± bladder irritability

· Haematuria

Ix

For all first time stone formers

· MSU, microscopy for RBC, WBC, casts, cyrstals

· Blds

— U&E, Ca++, uric acid, PO4-

· Retrieve and analyse stone

· Spot urinary cysteine test

· Xrays

— IVP

· CTU

— 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.

Complications

· Obstruction

· Infection

— pyonephrosis

v Obstruction + infection® urgent decompression with percutanous nephrostomy

Rx

· General

— Analgesia

— Antiemetics

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.

Follow-up

· 2 x fluid intake

· Metabolic evaluation

— Stone analysis

— 24hr urine

calcium, uric acid, oxalate, citrate, sodium, volume, pH

— Bloods

Urea, creatinine, calcium, phosphate, uric acid