A congenital megaureter is an abnormality characterized by a wide, dilated, and/or tortuous ureter, generally greater than 7 mm in diameter, usually seen in fetuses of more than 30 weeks' gestation up to children younger than 12 years. There are 4 categories of megaureter: obstructed, refluxing, obstructed and refluxing, and unobstructed and not refluxing. The primary condition is caused by an ureterovesical junction abnormality that impedes propagation of urine flow, while secondary megaureter is a functional ureteral obstruction caused by abnormal bladder or urethra conditions.

Boys are affected more often than girls. It occurs more commonly on the left side and occurs bilaterally in 20% of patients. Primary megaureter is the second most common cause of neonatal hydronephrosis. The condition is often detected antenatally during maternal ultrasonography.

Patients with unobstructed megaureter are typically asymptomatic. Findings of symptomatic patients first occur after infancy and include urinary tract infection (UTI), abdominal or flank pain, hematuria, uremia, or other indications of decreased kidney function.

Primary presentation of congenital megaureter in adults and adolescents is uncommon but has been reported. It is often discovered as an underlying condition during workup for UTI or renal stones.

Spontaneous resolution of primary megaureter is common, although less likely in patients with obstruction, infection, or associated renal injury.