Pyelectasis is the dilation or swelling of the renal pelvis, the funnel-shaped area inside the kidney where urine collects before moving to the ureter and bladder. This condition is a common observation during routine prenatal ultrasounds, affecting approximately 1% to 5% of pregnancies. Pyelectasis is often a mild finding that is temporary or resolves without intervention. It is a sign of a slightly backed-up urinary system, not a disease itself.
How Pyelectasis is Identified
Pyelectasis is diagnosed through fetal ultrasound, typically during the second-trimester screening around 20 weeks. Severity is determined by measuring the anteroposterior diameter (APD) of the renal pelvis, which quantifies the fluid buildup inside the kidney.
The criteria for diagnosis depend on gestational age. For pregnancies under 28 weeks, an APD of 4 millimeters or greater is diagnostic. After 28 weeks, a measurement of 7 millimeters or greater indicates pyelectasis. Mild cases, such as an APD between 4 mm and 10 mm, are typically referred to as pyelectasis, while more pronounced dilation may be classified as hydronephrosis.
Understanding the Underlying Causes
Pyelectasis causes fall into two primary categories: isolated and structural. In many mild cases, the cause is unknown, and the dilation is transient, resolving as the fetus matures. This isolated pyelectasis may be due to the natural immaturity of the fetal urinary tract or a temporary fold in the ureter.
Structural causes impede the normal flow of urine. The most common structural cause is a ureteropelvic junction (UPJ) obstruction, a blockage where the kidney pelvis connects to the ureter. Another element is vesicoureteral reflux, where urine flows backward from the bladder toward the kidney. Pyelectasis is also considered a “soft marker” for certain genetic conditions, such as Down syndrome (Trisomy 21). However, if pyelectasis is the only abnormality found, the risk for a genetic condition is low, and invasive testing is usually not recommended.
Monitoring and Treatment Options
The prognosis for pyelectasis is positive, as 80% to 90% of mild cases resolve spontaneously either before birth or within the first few months of life. The primary action following diagnosis is careful monitoring through serial ultrasounds later in the pregnancy.
Monitoring continues after birth with a postnatal renal ultrasound, typically performed within the first month, to confirm if the dilation has resolved or persists. If the condition is severe or persistent, the baby may be referred to a pediatric urologist or nephrologist. Prophylactic antibiotics may be prescribed to prevent urinary tract infection (UTI) risk caused by urine stasis. For rare, severe cases involving a confirmed obstruction damaging the kidney, surgical intervention, such as a pyeloplasty to relieve the blockage, may be necessary.