Caliectasis is the dilation (swelling) of the calyces, which are the cup-shaped structures inside your kidney that collect urine before it drains into the bladder. It’s not a disease on its own but a sign that something is blocking or slowing the normal flow of urine. The term often appears on ultrasound or CT reports, and if you’re reading this, you probably saw it on yours.
To understand what’s happening, picture the inside of your kidney as a funnel system. Urine forms in the kidney tissue, drips into small cups (minor calyces), flows into larger cups (major calyces), then empties into the renal pelvis and down the ureter to your bladder. When urine can’t drain properly, pressure builds and those cups stretch. That stretching is caliectasis.
How Caliectasis Relates to Hydronephrosis
You’ll often see caliectasis mentioned alongside hydronephrosis, and the two overlap. Hydronephrosis refers to dilation of the renal pelvis and/or the calyces. Caliectasis specifically describes dilation of the calyces. In practice, if your report says “caliectasis,” it means the swelling has reached deeper into the kidney’s drainage system rather than just affecting the pelvis at the center. When both the pelvis and calyces are dilated, the term “pelvicaliectasis” or “hydronephrosis” is used. Diffuse caliectasis, where both the central (major) and peripheral (minor) calyces are uniformly dilated, signals more advanced backup of urine.
Common Causes
Anything that blocks urine flow can cause caliectasis. The most frequent culprits fall into a few categories.
Kidney stones are one of the most common causes in adults. A stone lodged in the ureter or at the junction where the kidney meets the ureter physically blocks drainage, causing urine to pool and the calyces to swell.
Ureteropelvic junction obstruction (UPJO) is a narrowing where the renal pelvis connects to the ureter. It can be congenital or acquired. In the congenital form, the smooth muscle of the ureter may be arranged abnormally, creating a segment that doesn’t contract properly to push urine through. The ureter can also insert too high on the renal pelvis, making it difficult for urine to empty. In some cases, an extra blood vessel crossing near the lower part of the kidney kinks the ureter and interrupts flow.
Scarring and inflammation from chronic infections, prior kidney stones, or radiation therapy can thicken the ureter wall and narrow the passage over time.
External compression from masses or abnormal tissue outside the urinary tract can press on the ureter. This includes retroperitoneal fibrosis (a condition where scar-like tissue develops behind the abdomen), enlarged lymph nodes from cancers like lymphoma or testicular cancer, and tumors in the surrounding tissue.
Pregnancy is another common and typically harmless cause. The growing uterus can compress the ureters, and hormonal changes relax smooth muscle tissue, both of which slow urine drainage. This type of dilation usually resolves after delivery.
What It Feels Like
Mild caliectasis often causes no symptoms at all. Many people learn about it incidentally when imaging is done for another reason. When symptoms do appear, they typically come from the underlying cause rather than the dilation itself.
Flank pain, felt in the side or lower back, is the most common symptom when a blockage is significant. If a kidney stone is responsible, the pain can be intense and come in waves. When infection accompanies the obstruction, you may develop fever, chills, and pain in the back, side, or groin. Blood in the urine can also occur, sometimes visible as pink, red, or cola-colored urine, sometimes only detectable under a microscope during a urine test. Blood clots passing through the urinary tract can cause additional discomfort.
How It’s Diagnosed
Caliectasis is almost always discovered through imaging. Ultrasound is the first-line tool, especially for pregnant women and children, because it’s safe and widely available. It shows the degree of dilation in the renal pelvis and calyces clearly. CT scans provide more detailed images and are particularly useful for identifying the cause of the blockage, such as a kidney stone, tumor, or structural abnormality. Your doctor may also order blood tests to check kidney function and urine tests to look for infection or blood.
Severity Grading
Radiologists classify the dilation based on how far it extends into the kidney’s collecting system. Mild dilation may involve only the renal pelvis with slight stretching of the central calyces. Moderate dilation shows more prominent calyceal swelling. Severe or diffuse caliectasis, where both the major and minor calyces are uniformly dilated, suggests significant obstruction or prolonged pressure. In the most advanced cases, the kidney tissue itself begins to thin, which can compromise the organ’s ability to filter blood.
For prenatal cases specifically, the presence of peripheral calyceal dilation on a fetal ultrasound bumps the classification into a higher risk category, even if the measurement of the renal pelvis appears only mildly enlarged. This distinction matters because it changes what monitoring the baby will need after birth.
Treatment Depends on the Cause
Because caliectasis is a consequence rather than a standalone condition, treatment targets whatever is causing the blockage. If the dilation is mild and asymptomatic, monitoring with repeat imaging may be all that’s needed.
For kidney stones smaller than 2 centimeters, shock wave lithotripsy is a common first-line approach. It uses focused sound waves from outside the body to break stones into smaller fragments that can pass naturally. For larger or more complex stones, procedures like percutaneous nephrolithotomy (where a small incision in the back allows direct removal) or ureteroscopy (a thin scope threaded up through the urinary tract) offer high success rates with relatively low risk.
When a structural problem like ureteropelvic junction obstruction is the cause, surgery to widen or reconstruct the narrowed area may be necessary. If external compression from a mass or fibrosis is responsible, treating that underlying condition relieves the pressure on the ureter.
What Happens If It’s Left Untreated
Temporary or mild caliectasis that resolves on its own, such as during pregnancy, rarely causes lasting harm. Prolonged obstruction is a different story. When urine stays backed up in the kidney, it creates an environment where infections can take hold more easily. Kidney infections in this setting can damage the kidney tissue and lead to scarring.
Renal scarring carries real long-term consequences. High blood pressure develops in 10 to 30 percent of people with significant kidney scarring, sometimes taking up to eight years to appear. Scarring can also cause protein to leak into the urine, a sign that the kidney’s filtering units are under strain. Over time, the remaining healthy tissue compensates by working harder, which can accelerate further damage. In severe cases, this progression leads to significant loss of kidney function.
Caliectasis Found Before Birth
Dilation of the fetal urinary tract is the most common abnormality found on prenatal ultrasound, appearing in 1 to 5 percent of pregnancies. When caliectasis is detected in a fetus, follow-up depends on how severe the dilation appears. If peripheral calyceal dilation is present, the baby is typically classified in a higher risk group, prompting a repeat ultrasound one to three months after birth. In the highest risk category, where kidney tissue abnormalities accompany the dilation, follow-up imaging is recommended within one month, along with additional testing and preventive antibiotics to protect against urinary tract infections while the issue is being evaluated.
Many cases of prenatal urinary tract dilation resolve on their own as the baby’s urinary system matures. But close monitoring ensures that the cases requiring intervention are caught early, before kidney damage occurs.