Urinary diversion / ileal conduit:
Patients with diversion at higher risk of stones due to:
- Systemic metabolic acidosis – causes hypercalciuria and hypocitraturia.
- Chronic UTIs and urease producing organisms.
- Urinary stasis.
- Foreign bodies such as sutures, staple lines, and mucus.
- Hyperoxaluria if long segment of small bowel resected
Other issues including often already impaired renal function and high risks of developing infection, if not acutely infected.
Initial treatment should usually be with nephrostomy if presenting acutely.
- +/- antegrade stent simultaneously in elective setting, or once infection treated / renal functional stabilised in acute setting
Once stent is in situ, options include:
- PCNL or antegrade ureteroscopy
- Retrograde ureteroscopy via conduit/diversion using stent to locate UO
- ESWL – may have poor drainage, esp as left ureter passes under mesentery, and high risk of infection in these patients
NB for elective PCNL/antegrade access for diversions, will not be able to easily pass retrograde ureteric catheter for contrast for puncture – best to get radiologist to puncture or put in nephrostomy first.
Transplant
1 % incidence of stones in transplant kidney.
Risk factors for stone formation:
- Secondary or tertiary hyperparathyroidism (resulting hypercalciuria)
- Recurrent UTI and immunosuppression
- Cyclosporin can cause hyperuricosuria
- Hyperfiltration can increase urinary electrolyte levels
These patients are very susceptible to renal insult with obstruction and infections.
Often present late and atypically – graft is not innervated so pain is atypical, and may just be due to stretch or inflammation of pseudocapsule.
Transplant kidney is most often native left placed in right fossa – so posterior calyces become anterior.
Management options:
- Observation – generally not an option given single kidney and lack of innervation and hence usual warning pain of obstruction
- ESWL – generally not – graft close to pelvic bones and bowel, steinstrasse would be bad, performed prone
- Stent if doing ESWL
- Ureteroscopy
- May be difficulty locating neo-UO – and may be difficult accessing
- May need adjuncts like Kumpe catheters or cobra catheters
- PCNL
- Access best achieved supine under US or CT guidance to avoid bowel (and iliacs)
- Scarred pseudocapsule may be difficult to dilate
- Use flexible ureteroscopes rather than large rigid instruments – graft is fixed and torque could be catastrophic
Horseshoe kidney
Common – 1 in 400. Horseshoe kidneys often sit lower in abdomen, with ascent arrested by IMA.
Stones very common in horseshoe kidneys – may be 20 % even up to 60 %
Renal pelvises are usually anterior, calyces point posteriorly, and ureters may insert quite high on renal pelvis – all predisposing to stasis and stones.
PUJ obstruction more common cf. non-horseshoe kidneys.
Options:
- Observation – reasonable strategy in renal stones as per normal kidneys
- ESWL
- Potentially poor clearance due to posterior calyces, high ureters and subsequent poor drainage
- May be more difficult to target due to location, and aberrant blood supply/vasculature
- Ureteroscopy
- Good option but lower pole stones may be difficult to access with deflection
- Consider single use flexible ureteroscopes
- PCNL
- Good SFR
- Adapt technique due to different anatomy – calyces more posteriorly oriented, abnormal relation of ureter and other organs
- Upper pole access preferred – usually subcostal
- Laparoscopic guided access can be useful
- Kidney may be deeper than normal kidneys – have long sheaths etc available especially in bigger patients
Pelvic or ectopic kidneys
Locations and orientations can be variable – rotation can be quite bizarre.
Deep pelvic locations mean intraperitoneal bowel at risk if performing PCNL – lap assisted puncture may be useful.
Open or laparoscopic ureterolithotomy or pyelolithotomy may be best option.
Polycystic kidneys
5 – 10 x greater risk of stones cf. normal population.
Typically acidic urine with low citrate and low magnesium. Uric acid stones common.
Urinary stasis may result from compression of parenchyma from cysts.
ESWL ?concern for haemorrhagic cysts or rupture – not been borne out in literature.
PCNL similar – risks of cyst rupture and haemorrhage are theoretical and not proven.