Stone disease
Key points
Infective stones
Bacteria split urea to ammonia - forms ammonium salts
Magnesium phosphate + ammonium phosphate + calcium phosphate
Proteus mirabilis (gram negative rod) infection is associated with stone formation
Metabolic stones
More solid - less 'gelatinous' matrix
Calcium stones:
Idiopathic Hypercalciuria most common cause of metabolic stones
No effect on serum Calcium
Reduced citrate levels predispose to calcium stones
Citrate binds to and solubilises calcium
Oxalate stones:
Hyperoxaluria - Primary is autosomal recessive condition
Hepatic enzyme deficiency
Type 1 100% end stage renal failure - need renal and liver transplant
Types 2&3 less severe
Secondary Oxaluria can be due to malabsorption syndromes e.g. Crohns disease, short gut, cystic fibrosis
Cysteine stones:
Autosomal recessive
Cysteine excreted in high volumes in proximal tubule
Most form pure cystine stones
Often larger and more frequent stones compared to calcium stones
Greater disease and operative burden - more likely to develop chronic renal failure compared to those with calcium stones
Morner test can be used to test for cysteine - turns purple when mixed with with sodium nitroprusside + cyanide
Standard scenario
Initial diagnosis of stone
Main concern is renal function
Assess and manage for:
1. Sepsis
2. Dehydration
3. Pain
Extra examination for XGP:
Painful flank mass, cutaneous fistulae
Find cause of stone:
History -UTIs, Dietary and water intake, symptoms of hypercalcaemia
Family history - Calciuria (dominant), Hyperoxaluria (recessive), homocysteinuria (recessive)
Investigations
Bloods (Calcium/Urate)
Send stone if passed
USS
CT KUB to delineate
If staghorn or XGP suspected - do DMSA
Known stone formers -
Can get X-ray KUB for radio-opaque stone assessments
Stone MDT
Management
<0.5cm conservative
0.5-1cm discuss with family regarding management preference
>1cm likely needs intervention
Pelvicalyceal stones:
Percutaneous nephrolithotomy (PCNL)
Request help of uro-radiologist and experienced stone surgeon in theatre
Cystoscopy and ureteric access catheter
Catheterise + tape both together
Position prone or supine with side up depending on table USS findings
USS + fluoroscopic access through cortex
Dilate tract and insert metal sheath
12-24Fr Nephroscope and Holmium laser to fragment
Use vortex effect to remove stones
Nephrostomy/JJ stent if lots of fragments needing to pass - remove in 6 weeks
Ureteric stone:
Laser Ureterorenoscopy 4.2Fr scope
If laser not available - cystoscopy and stent
Nephrostomy if septic and obstructed upper tract
References
Essentials of Pediatric Urology, 3rd edition, 2022, Chapter 11 Urinary Tract Calculi
Leslie SW, Sajjad H. Hypercalciuria. [Updated 2024 Feb 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK448183/
Shah A, Leslie SW, Ramakrishnan S. Hyperoxaluria. [Updated 2024 Mar 4]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK558987/
Leslie SW, Sajjad H, Nazzal L. Cystinuria. [Updated 2023 May 30]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470527/