Duplex Kidney
A duplex kidney, also called a duplicated collecting system, is a common anatomical variation in which a kidney has two drainage systems instead of one. This may involve two ureters draining the kidney or a single ureter that splits internally. Most people with a duplex kidney have no symptoms and discover the condition incidentally on imaging. In some cases, however, duplication can be associated with urinary tract infections, obstruction, or reflux.
What is it?
A duplex kidney forms when the kidney develops two collecting systems—structures that drain urine from the kidney into the ureter. In some cases, there are two completely separate ureters that enter the bladder independently. In others, the ureters join before reaching the bladder. Most duplex systems function normally, but depending on the anatomy, they may be more prone to obstruction, reflux, or infections.
Imaging helps determine whether duplication is complete or partial, whether both drainage systems function properly, and if any complications are present. Ultrasound often detects the duplicated system, while CT or MRI provides detailed anatomical information. VCUG may be used to assess for reflux in children or adults with recurrent infections.
Important to Know
Most duplex kidneys cause no medical issues and require no treatment. Problems arise only when the duplicated system leads to urine blockage, recurrent infections, or reflux. Children may be diagnosed at a young age due to urinary symptoms, but many adults learn they have a duplex kidney only after imaging for unrelated reasons.
Red flag symptoms include frequent urinary tract infections, fever, flank pain, blood in the urine, difficulty urinating, or persistent abdominal or pelvic pain. These may indicate obstruction, reflux, or infection requiring further evaluation.