Anatomy just got a little more complicated. It turns out humans might have an organ that was never before recognized by science: the interstitium.

The interstitium was previously believed to be made of dense layers of tissue, but new research published in the journal Scientific Reports indicates that the tissue bundles are actually a network of a tiny, fluid-filled channels connected throughout the human body. Dr. Neil Theise, a pathologist at New York University School of Medicine, told The New Scientist that the organ is essentially a fluid-filled “shock absorber” that surrounds tissue throughout the body. If verified, the interstitium could become the largest known organ in humans.

The discovery of the interstitium is potentially significant in understanding how cancer cells are transported around the body, according to an analysis in The New Scientist. Invasive cancer cells could be spreading beyond their originally infected tissues through the fluid-filled channels of the interstitium and lead directly to the lymphatic system.

“Once they get in, it’s like they’re on a water slide,” Theise told The New Scientist. “We have a new window on the mechanism of tumour spread.”

The confirmation of the potentially game-changing discovery rests on a consensus from the scientific community that the interstitium qualifies as an organ as researchers study it further, Theise told Live Science. It was first discovered by Dr. David Carr-Locke and Dr. Petros Benias at Mount Sinai Beth Israel medical center in New York City when the doctors were examining a patient's bile duct for cancer, according to Live Science. The doctors noticed microscopic interconnected passages in the patient’s tissue and began to question what they were looking at. Along with Theise and a team of scientists, they uncovered the “previously unappreciated” interstitium.

“There’s something new here,” Theise told The Daily Beast. “No one’s ever seen it before, but it’s been there the whole time.”

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