From the Guidelines
Yes, imaging should be repeated for two nonobstructing 0.5 cm renal stones. According to the most recent guidelines, active surveillance of asymptomatic, non-obstructing caliceal stones is possible, and follow-up imaging is recommended 1. The European Association of Urology (EAU) guidelines suggest that active surveillance is acceptable for stones up to 15 mm.
Key Considerations
- Follow-up imaging is typically recommended in 6-12 months to monitor for stone growth or development of new stones.
- The preferred imaging modality is a low-dose CT scan without contrast, though ultrasound may be used for patients concerned about radiation exposure 1.
- During this monitoring period, patients should increase fluid intake to at least 2-2.5 liters per day, limit sodium intake to less than 2,300 mg daily, and moderate animal protein consumption.
- A 24-hour urine collection may be beneficial to identify specific metabolic abnormalities contributing to stone formation.
Importance of Monitoring
Regular monitoring is important because even small, asymptomatic stones can grow over time or cause complications such as obstruction, infection, or renal damage if left unmonitored. If stones grow, increase in number, or become symptomatic, more aggressive intervention such as ureteroscopy or shockwave lithotripsy may be necessary. The American College of Radiology (ACR) recommends noncontrast CT (NCCT) as the imaging study of choice for initial evaluation of patients with acute onset of flank pain and suspicion of stone disease without known prior stone disease 1.
Patient Management
- Patients with nonobstructing renal stones should be managed conservatively with supportive and medical therapy, unless stone growth, associated infection, or specific situations such as vocational reasons necessitate surgical treatment 1.
- Surgical treatment of renal stones depends on stone size and location, with percutaneous nephrolithotomy (PCNL) and flexible ureteroscopy (fURS) being recommended for stones less than 20 mm 1.
From the Research
Imaging for Nonobstructing Renal Stones
- The provided studies do not directly address the question of whether imaging should be repeated for 2 nonobstructing renal stones of 0.5cm in size.
- However, some studies discuss the factors that influence the treatment outcomes of extracorporeal shock wave lithotripsy (ESWL) for renal stones, such as stone size, location, density, and skin-to-stone distance 2, 3, 4, 5.
- One study found that stone density on native CT scans can predict treatment outcomes in ESWL, with lower density stones being more likely to be cleared 3.
- Another study found that the distance from skin to stone, as measured by CT scans, can affect the stone-free rate achieved via ESWL, with shorter distances being associated with higher success rates 4.
- A study comparing Flexible Ureteroscopy, ESWL, and Mini Percutaneous Nephrolithotomy for managing lower pole renal hard stones ≤ 2 cm found that Flexible Ureteroscopy and Mini PCNL had higher stone-free rates than ESWL, but the study did not specifically address the question of imaging for nonobstructing renal stones 6.
- A retrospective study on ESWL found that stone size, location, and mean attenuation value (MAV) correlated with treatment outcomes, but the use of non-contrast-enhanced CT scan (NCCT) did not provide substantial advantages compared to relying solely on kidney-ureter-bladder film (KUB) 5.