What is the recommended treatment for a patient with an ectopic, low-lying right kidney and a 12 x 10 mm stone in the renal pelvis causing mild hydronephrosis?

Management of Renal Pelvis Stone in an Ectopic Low-Lying Kidney

For a patient with an ectopic, low-lying right kidney and a 12 x 10 mm stone in the renal pelvis causing mild hydronephrosis, flexible ureteroscopy (URS) with holmium laser lithotripsy is the recommended first-line treatment. 1, 2

Treatment Decision Algorithm

Stone Characteristics Assessment:

• Stone size: 12 x 10 mm (medium-sized)
• Location: Renal pelvis
• Density: 1176 HU (high density)
• Complicating factor: Ectopic low-lying kidney
• Presence of mild hydronephrosis

Treatment Options Analysis:

1. Flexible Ureteroscopy (URS)

   • Preferred for this case due to:
     • Stone size between 10-20 mm 1
     • Abnormal renal anatomy (ectopic kidney) 2
     • High stone-free rates for renal pelvis stones (81-94%) 1
   • Advantages:
     • Superior access to challenging locations with abnormal anatomy 2
     • Less invasive than PCNL
     • May require staged procedures but safer in this anatomical variation

2. Shock Wave Lithotripsy (SWL)

   • Not recommended because:
     • Ectopic kidney location makes targeting difficult
     • Stone size >10 mm (reduced efficacy) 1
     • High stone density (1176 HU) predicts poor fragmentation 1

3. Percutaneous Nephrolithotomy (PCNL)

   • Generally indicated for stones >20 mm 1
   • In ectopic kidneys, requires specialized approaches:
     • Laparoscopy-assisted PCNL may be considered as a second-line option 3, 4
     • Higher risk of complications due to abnormal anatomy and vascular relationships

Pre-Procedure Considerations

• Imaging requirements:

  • CT urography to fully characterize the ectopic kidney's anatomy
  • Assessment of vascular supply and relationship to surrounding structures
  • Evaluation of the ureter course (often abnormal in ectopic kidneys) 2, 5

• Laboratory evaluation:

  • Mandatory urine culture to rule out infection 2
  • Serum creatinine to assess baseline renal function
  • Complete blood count and coagulation profile

Procedure Details

• Approach:

  • Flexible ureteroscope is essential due to the abnormal course of the ureter in ectopic kidneys 2
  • Gentle manipulation to minimize risk of ureteral injury
  • Holmium laser lithotripsy for stone fragmentation
  • Complete stone removal or fragmentation to <2 mm pieces

• Technical considerations:

  • May require specialized access techniques due to abnormal ureteral course
  • Higher risk of perforation (6%) compared to normal anatomy 2
  • Post-procedure stenting is strongly recommended due to:
    • Anatomical abnormalities
    • Risk of edema and obstruction
    • Potential need for staged procedures

Post-Procedure Management

• Ureteral stent placement for 1-2 weeks
• Close follow-up within 1-2 weeks
• Post-procedure imaging to confirm stone clearance
• Metabolic evaluation to prevent recurrence

Important Caveats

• Risk of complications:

  • Ectopic kidneys have higher rates of obstruction, infection, and stone formation 5, 6
  • Stricture formation risk of approximately 2% 2
  • Multiple procedures may be required for complete stone clearance

• Alternative approach:

  • If URS fails or is technically not feasible, laparoscopic pyelolithotomy has shown excellent results (100% stone-free rates) in ectopic kidneys 4
  • Laparoscopy-assisted PCNL may be considered for larger stones or complex cases 3

• Infection management:

  • If infection is suspected at any point, urgent drainage of the collecting system is mandatory before definitive stone treatment 2

By following this approach, the patient can expect the best outcomes in terms of stone clearance while minimizing the risks associated with treating stones in an ectopic kidney.