Scientists May Have Identified a New Human Organ

It is called the interstitium, and it consists of fluid-filled cavities that can be found throughout the body

Dermal interstitium
The above image shows the dermal interstitium with bundles of collagen and fluid (white spaces). Neil Theise

In 2015, two doctors at New York City’s Mount Sinai-Beth Israel Medical Center were examining a patient’s bile duct when they noticed something curious: a network of fluid-filled cavities within the tissue layer that was not consistent with any previously described anatomy. Further research revealed that these cavities can be found throughout the human body and, as Rachael Rettner of Live Science reports, scientists at New York University’s School of Medicine believe the anatomical discovery should be classified as a new organ.

In a new paper in Scientific Reports, researchers write that the “interstitium”—as they have dubbed the possible new organ—consists of an interconnected series of fluid-filled spaces, which are “supported by a complex network of thick collagen bundles.”

Neil Theise, a professor of pathology at New York University Langone School of Medicine and one of the study authors, tells Rettner that the interstitium is akin to an "open, fluid-filled highway," and it can be found just about everywhere in the body. It lines the digestive tract, urinary system, lungs and muscles. It has been identified in connective tissues, including those just below the surface of the skin.

Previously, scientists had a vague notion that a network of spaces might hold fluid that exists outside of cells, but they had never been able to observe it. Researchers traditionally study tissue using biopsies that have been treated with chemicals, sliced into thin layers and dyed to highlight certain features. But this process causes the fluid-filled cavities to collapse. The researchers involved in the recent study instead relied on a relatively new technique called a confocal laser endomicroscopy, which, as Alice Park of Time explains, allowed them to study living tissue—and helped them get a good look at the interstitium.

The authors of the study have labeled their discovery a new organ, but this is not an official classification. For that to happen, Theise tells Rettner, a consensus will have to be reached among other groups of researchers. And not all experts are sure that it is accurate to call the interstitium an organ. Jennifer Munson, a biomedical engineer at Virginia Tech tells Sarah Gibbens of National Geographic that while the new paper demonstrates “the benefit of having new ways to image and look at tissues,” further research into the interstitium’s function is warranted.

“I'm really excited about the find but, as with all scientists, I approach everything with a little skepticism,” she says.

New organ or not, the interstitium appears to play an important role in the body. Thiese tells Gibbens that he believes the interstitium works like a “shock absorber,” protecting the tissue. Researchers also believe that the interstitium drains into the lymphatic system and acts as a source of lymph, a fluid that moves through the lymphatic system and removes bacteria from tissues. This might explain why some cancers that invade the tissue spread into the lymph nodes, so learning more about the interstitium could have significant implications for cancer research.

“Can we detect [disease] earlier by sampling fluid from the space?” Theise asks, according to Gibbens. “Can we figure out mechanisms to stop spread?”