For 20 years, an unnamed patient suffered from urinary frequency, but lab findings didn’t show anything. Then, doctors at the Washington, D.C. VA Medical Center discovered a large, egg-like mass in his abdomen.

A computed tomography (CT) scan on the patient’s abdomen and pelvis found a 3.3-inch mass, according to a study published Tuesday in The New England Journal of Medicine. The free-floating, smooth, firm, rubbery mass measured 3.9 inches by 3.7 inches by 2.9 inches and weighed 7.7 ounces.  

The mass was identified as a peritoneal loose body, which occurs when small pieces of fat in the abdomen detach from surrounding structures and loose blood supply. The fat calcified and turned into a fibrotic mass, which is completely benign, researcher Dr. Rachael Sussman of Georgetown University Hospital, told FoxNews.com in an e-mail.

“Small peritoneal bodies are quite common, but this is the largest reported one in the literature to date,” Sussman said.

The patient’s urinary frequency was resolved immediately after surgical removal of the mass. Most periotonal bodies are so small that they do not cause symptoms, but when they become large enough, they have been reported to cause small bowel obstruction and urinary retention.

According to researchers, this is the first case to report urinary frequency as a symptom. The patient had no other side effects from the mass, which compressed his bladder.

After removing the mass, researchers used green ink to delineate its makeup of proteinaceous material with fibrinoid necrosis, surrounded by a ring of calcification.