Natural history of asymptomatic renal stones
Incidence 5 – 10 % in screened populations.
Natural history of non obstructing smaller renal stones is unclear and poorly defined.
Campbell’s numbers (studies range widely):
Risk of progression (increasing size or developing symptoms):
- Seems to be about 50 % or more over 5 years
Spontaneous stone passage:
- Occurs about 15 % of the time
Risk of surgical intervention:
- 10 – 20 % after 3 – 4 years (Campbell’s)
- 10 – 25 % per year, with cumulative probability 48 % at 5 years (EAU)
Renal pelvis stones and larger stones are more likely to end up needing surgery.
EAU guidelines:
- Initially repeat imaging at 6 months, then annually in the lack of symptoms and stone growth
- Offer treatment if there is:
- Growth in stone size
- Pain
- Obstruction
- Infections
Indications for active treatment of renal stones:
- Symptoms – pain, obstruction, infection, haematuria
- > 15 mm (essentially all go on to cause problems on observation)
- Growth of stone on surveillance (especially > 5 mm)
- High risk patients – including occupations, CKD, recurrent formers
- Patient preference including social settings, travel
- Single kidneys
Options for managing renal stones once decision for active treatment has been made – ESWL, URS, PCNL, rarely open/laparoscopic/robotic surgery.
Issues with lower pole stones
These can be difficult to treat with ESWL or ureteroscopy.
ESWL for stones in lower pole has significantly lower clearance rates than other stones – even if the stone fragments nicely, fragments may remain in the lower pole calyx and act as a nidus for ongoing stone formation.
Ureteroscopically these stones can be challenging to reach, requiring excessive angulation which may obscure vision and difficulty passing the laser.
Unfavourable anatomical features include:
- Acute infundibulopelvic angle < 90 degrees
- Long infundibular length
- Narrow infundibular width < 4 mm
With newer scopes, lower pole stones are often more accessible with URS, but fragments still don’t drain well.
Lower Pole 2 study compared ESWL and URS for lower pole stones < 1 cm – published 2005 – 50 % SFR for URS, 35 % ESWL (not significant) – ESWL better tolerated / less complications.
PCNL has highest stone free rates for lower poles (with trade-off of morbidity and invasiveness) – perhaps mini-PCNL will be treatment of choice in future.
Percussion / inversion / diuresis therapy (hyperhydration or Lasix) probably helps with passage of small fragments after treatment of LP stone.