What is the recommended treatment for a 17mm renal calculus with an associated 11mm cyst and suspected milk of calcium?

Treatment of 17mm Renal Calculus with Suspected Milk of Calcium

If this is confirmed to be milk of calcium in a renal cyst, percutaneous nephrolithotomy (PCNL) with suction is the definitive treatment, as these soft stones can be retrieved without fragmentation and shock wave lithotripsy will be unsuccessful. 1

Diagnostic Confirmation First

Before proceeding with treatment, you must confirm whether this is truly milk of calcium versus a standard renal calculus:

• Obtain a non-contrast CT scan if not already done - this is essential to differentiate milk of calcium from a typical stone 1, 2

• Look for characteristic CT findings of milk of calcium:

  • Low Hounsfield units (typically 114-612 HU, much lower than typical stones) 1
  • Dependent positioning in the posterior aspect of dilated calyces due to gravitational layering 1, 3
  • Fluid level or semilunar (half-moon) pattern on the anterior surface 1, 2
  • The stone may appear faintly radio-opaque or even radiolucent on plain films 1

• Obtain upright plain films if CT is equivocal - milk of calcium will show characteristic layering or half-moon contour that changes with position 2

Treatment Algorithm

If Milk of Calcium is Confirmed:

Proceed directly to PCNL with suction 1

• Do NOT attempt shock wave lithotripsy - it will fail because milk of calcium is a viscous colloidal suspension of calcium salts that cannot be fragmented 1, 2
• PCNL allows retrieval of the soft stone material without need for disintegration 1
• All seven cases in the largest reported series were successfully treated with PCNL and suction alone 1
• Obtain preoperative urine culture as infection is a predisposing factor 1

If This is a Standard 17mm Renal Calculus (Not Milk of Calcium):

Both ureteroscopy (URS) and shock wave lithotripsy (SWL) are acceptable first-line treatments for stones >10mm, though URS yields significantly higher stone-free rates with a single procedure 4

• For stones >10mm, most will require surgical treatment rather than observation 4
• Ureteroscopy advantages: Higher stone-free rates with single procedure 4
• Ureteroscopy disadvantages: Higher complication rates including 1-2% stricture risk and 3-9% ureteral injury risk depending on location 4
• SWL considerations: Lower stone-free rates, may require multiple procedures, but lower complication rates 4

Critical Pitfalls to Avoid

• Never attempt SWL for confirmed milk of calcium - this will result in treatment failure and unnecessary patient morbidity 1, 2
• Do not rely on ultrasound alone - milk of calcium can appear as a simple cyst when completely filling the cyst, or may be misinterpreted as a standard calculus 5, 3
• Do not proceed with surgery based solely on plain radiography - two reported cases underwent unnecessary surgical intervention because milk of calcium was misinterpreted as renal lithiasis 2
• Obtain proper imaging in multiple positions - the characteristic layering effect may only be apparent on upright films or CT 2

Management of the Associated 11mm Cyst

• If milk of calcium is confirmed, the cyst and stone are managed together during PCNL - the entire colloidal suspension is evacuated 1
• Milk of calcium typically forms in obstructed or dilated calyces/cysts where stasis allows calcium salt precipitation 1, 3
• When asymptomatic and definitively diagnosed, milk of calcium requires no treatment - but at 17mm with symptoms prompting evaluation, intervention is appropriate 3, 6