Calyceal Diverticulum Formation
Calyceal diverticula form due to congenital abnormalities during ureteral bud development, resulting in outpouchings of the upper collecting system that communicate with the renal calyces through a narrow neck. 1, 2
Pathogenesis
The formation mechanism is fundamentally congenital in origin rather than acquired:
Developmental anomaly: CD arise from abnormalities during the embryologic process of ureteral bud formation, creating abnormally dilated calyces caused by a narrowed infundibulum 1, 3
Structural characteristics: These are outpouchings lined by transitional epithelium that maintain communication with the collecting system through a narrow channel or neck 2
Clinical Context
Understanding the congenital nature has important implications:
Prevalence: While historically reported at 0.21-0.45% incidence, recent pediatric series suggest CD may comprise up to 5% of all renal cystic lesions, indicating they are more common than previously recognized 3, 4
Demographics: There is a female preponderance (67%), and bilateral involvement occurs in approximately 14% of cases 3
Stone formation: The narrow communication predisposes to urinary stasis, with stones found in up to 50% of calyceal diverticula in reported series, though 96% of symptomatic patients present with stones 2
Diagnostic Pitfall
A critical caveat: CD are frequently misdiagnosed as simple renal cysts or parapelvic cysts on initial imaging 4. The key distinguishing feature is demonstrating communication with the pelvicalyceal system, which requires:
- Delayed-phase imaging on intravenous urography or CT urography 5
- Contrast MR urography with postcontrast images at 5 minutes to visualize the connecting neck 4
- Measurement of aspirated fluid creatinine levels (significantly elevated compared to serum) when diagnosis remains uncertain 5
The congenital origin explains why these lesions are present from birth but may only become symptomatic later when complications like infection, obstruction, or stone formation develop 1.