This anomaly can go unnoticed for years and is usually diagnosed only accidentally. Such is the case of an 18-year-old man who recently showed up at an emergency room in New Delhi with symptoms of bowel obstruction. In examining a scan of his abdomen, doctors saw that his kidneys are joined in the middle and sit just above his bladder, according to a report published last week by the medical journal BMJ Case Reports.

There are multiple types of kidney or renal fusion, and pancake kidney, which is more common among men, is the most extreme, accounting for less than 10 percent of anomalies, according to the report.

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A similar case was reported in New Delhi in 2014, when a 19-year-old woman showed up at a hospital’s outpatient department with pain in her lower abdomen, fever and a burning sensation when she urinated. A scan showed a fused mass — her kidney — in her pelvic cavity.

In another case reported in Jordan last year, a 32-year-old man showed up at a clinic with abdominal pain. An ultrasound and a CT scan showed that his kidney was one flat, nearly rectangular mass located on the right side of his abdomen.

A more common type of kidney fusion is called the horseshoe kidney, in which the lower sides of two kidneys fuse during the early stages of development and form one U-shaped organ. There’s also the L-shaped kidney, in which an abnormal kidney is positioned horizontally and attached to the bottom of the normal one. In some cases, one kidney goes directly below the other, forming a vertical organ.

Having a fused kidney does not mean the organ will fail, and doctors generally don’t recommend invasive surgeries to correct it. Kidney functions tend to be normal, and since most people don’t show symptoms, doctors prefer regular checkups to make sure the kidneys are functioning properly.

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Those with these abnormalities, however, are more prone to urinary tract infection and urinary stasis, or the inability to empty the bladder. They’re also more likely to develop certain cancers, such as Wilms tumor, a kidney cancer common among children; renal cell carcinoma, which is common among older men; and rhabdomyosarcoma, a rare cancer that forms in soft tissue, according to the BMJ Case Report.

Someone with a horseshoe kidney, for example, is almost twice as likely to have Wilms tumor as someone with normal renal anatomy, according to the report. In the case of a pancake kidney, however, cases are so rare that it’s impossible to determine the likelihood of developing cancer.