Man Discovers He Has Three Kidneys After Visiting Doctor for Back Pain

A man in Brazil discovered he had an extra kidney after he had a scan to diagnose his back pain, according to a case report.

The unnamed 38-year-old man visited an outpatient clinic at a hospital in the Brazilian city of São Paul, complaining of severe pain in his lower back. His doctors, Dr. Jose Medina-Pestana and Dr. Renato Foresto of the Hospital do Rim, detailed his case in the New England Journal of Medicine.

His doctors performed a number of tests on the man in a bid to find the source of his discomfort, including a CT scan.

kidney, stock, getty
A stock image shows a model kidney next to a stethoscope in a doctor's office. Getty Images/KARIM SAHIB/AFP

The results revealed the man had three kidneys. As well as a left kidney, which appeared normal, he had two which were fused together and positioned in his pelvis.

Like most people with additional kidneys, the man didn't have any specific symptoms which suggested anything was wrong. Instead, he only discovered his abnormality because of the CT scan to diagnose his back pain.

The man's back pain was attributed to a herniated disk, also known as a bulging, protruding, or ruptured disk, unrelated to his kidneys. Doctors treated his back problem with pain medicine.

Referring to the tube which carries urine from the kidneys to the bladder, the team wrote: "The ureter from the left pelvic kidney joined the ureter from the other left kidney just above its entrance into the bladder. The ureter from the right pelvic kidney entered the bladder on the right side."

The man's kidneys were found to function normally, wrote Medina-Pestana and Renato Foresto.

The team described the man's condition as "uncommon." They believe he grew three kidneys due to a problem during embryogenesis, the term used to describe the first eight weeks when an embryo develops a sperm fertilizes an egg.

It is possible the duplicate left kidney divided from the other cells in the womb too soon. The right and lower left kidneys then likely fused together and didn't rise into the correct position as they developed. Instead, they sat in the pelvic area, according to his doctors.

Having three kidneys is also known as a "duplex kidney," from the Latin for "double." According to the National Kidney Foundation, having three kidneys is relatively uncommon, and usually only discovered by accident.

"It can be associated with infections and kidney stones, but usually causes no symptoms at all," the organization states on its website.

Dr. Julie Wright-Nunes, chair of Medical Affairs for the American Kidney Fund who was not involved with the case study, told Newsweek: "Although there are not exact statistics for how many people have three kidneys, this is because unless a person has imaging done, they likely do not know they have three kidneys."

Wright-Nune, who is also assistant professor at the University of Michigan Health System in the Department of Internal Medicine, Division of Nephrology, said: "Most often there usually are no symptoms. Having three kidneys is not thought to be a harmful condition, either. When people do have symptoms related to three kidneys or some other types of uncommon kidney development, the more typical symptoms might be from urine tract issues or infections or kidney stones. Then these issues prompt investigation and discovery."

This article has been updated with comment from Julie Wright-Nunes.