Learning Radiology xray montage

Congenital Megacalyces


General Considerations

  • Rare; more common in males
  • Congenital
  • Usually unilateral
  • Underdevelopment of medullary pyramids
  • No obstruction
    • The renal pelvis and ureter are usually normal
  • Rarely associated with megaureter which is an obstructive uropathy occurring near the ureterovesical junction

Clinical Findings

  • Near-normal renal function
  • Often symptom-free
  • Stasis in calyces may predispose to infection and stones

Imaging Findings

  • Since the medullary pyramids are underdeveloped, the calyx is enlarged and flattened or convex instead of concave
  • Kidney may be larger than normal
  • Frequently more calyces than normal
  • Calyces are facetted, fitting together as pieces of a puzzle
  • Renal medulla is thinner than normal but cortex retains its normal thickness and function

Differential Diagnosis

  • Hydronephrosis – the renal pelvis is general not enlarged with megacalyces but is with hydronephrosis


  • Not progressive
  • No treatment is usually necessary

 Congenital Megacalyces

Congenital Megacalyces. Maximum Intensity projection Image of a CT urogram shows numerous dilated, polygonal-shaped calyces in the left kidney with convex outer margins (red arrows). The calyces fit together like pieces of a puzzle. The renal pelvis (white arrow) is not dilated and the ureter is normal in size (yellow arrow) helping to differentiate this from a cause of obstructive hydronephrosis.

The Coexistence of Congenital Megacalyces and Primary Megaureter. B Vargas and RL Lebowitz. AJR 147:313-316 August 1986.


Talner LB, Gittes RF. Megacalyces. Clin Radiol. 1972;23(3):355-361.