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

Treatment

• Not progressive
• No treatment is usually necessary

 
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.