Doctors examining a man with back pain discovered the cause of that particular malady—and also stumbled across an odd bonus find. IFLScience reports on a case study published last week in the New England Journal of Medicine that details how a 38-year-old man in Sao Paulo, Brazil, showed up at a hospital to complain about his back discomfort. Doctors performed a CT scan to see what was up and found the patient had a herniated (aka "slipped") disk, which is a common cause of back problems. Then, per Live Science, doctors spotted an additional "unusual anatomical feature": not two kidneys, but three. His left kidney was normal, but the other two had fused together near the pelvis. The normal left kidney's ureter tube, which transports urine to the bladder, joined up with the left pelvic kidney's ureter before entering the bladder; the right pelvic kidney had its own ureter right to the bladder.
The disorder, known as supernumerary kidney, is "one of the rarest of all pathologic renal conditions," per a case study from 1915, with fewer than 100 cases cited in medical literature. Newsweek, which notes this anomaly is usually discovered by accident, reports that the doctors in this patient's case think the condition arose in embryogenesis during the first eight weeks of pregnancy, when the extra left kidney may have divided from other cells too early and merged with the right kidney. "We had never seen anything like this," Renato Foresto, one of the case study's authors, tells IFLScience. "The surprise was great, followed by concern there was something wrong with the patient's health." But despite the weirdness of such an organ fusion, doctors determined the man had normal kidney function and no other health problems other than his slipped disk, which they treated with oral painkillers. (Read more discoveries stories.)