Congenital megacycles or megacalycosis is a rare congenital disease caused by the underdevelopment of renal medullary pyramids.

Radiographic features of the disease:

• numerous crowded dilated, and polygonal renal calyces which show convex outer margins (secondary to the absence of medullary pyramids)
• the renal pelvis and ureter are of normal size helping to distinguish megacalyces from hydronephrosis.