Calyceal dilation refers to the widening or ballooning of the calyces, the cup-shaped collecting structures within the kidney that funnel urine into the renal pelvis. On ultrasound, dilated calyces appear as rounded, anechoic spaces within the renal sinus, replacing the normally bright, compact appearance of the central kidney. Calyceal dilation is typically one of the earliest signs of hydronephrosis, indicating that urine is backing up in the kidney, often due to an obstruction downstream such as a kidney stone in the ureter. The degree of calyceal dilation helps sonographers and physicians grade the severity of hydronephrosis from mild to severe.
Sonography Term