Study says we have an undiscovered organ. It’s called the interstitium

These compartments are found beneath the skin, as well as lining the gut, lungs, blood vessels and muscles, and join together to form a network supported by a mesh of strong, flexible proteins.

Researchers say they didn’t see the spaces prior because they were examining tissue on slides. The method now used to study tissue involves samples being sliced thinly and then treated with chemicals.

While this may make certain structures more apparent, it drains away any existing fluid.

Scientists claim that a network of fluid-filled spaces in connective tissue is actually the body’s largest organ. The remaining fluid is “interstitial”, and the current study is the first to define the interstitium as an organ in its own right, and as one of the largest of the body, say the authors.

“I think what the paper shows is the benefit of having new ways to image and look at tissues”. Upon further scrutiny, they determined that the lattice is composed of collagen bundles that support fluid-filled spaces and are lined irregularly with flattened cells that produce two markers, one endothelial and one mesenchymal.

A federal panel of elite scientists reported in 2016 that focusing on the immune system could be the key to finding highly effective treatments for cancer. For example, the findings appear to explain why cancer tumors that invade this layer of tissue can spread to the lymph nodes.

The interstitial space is the major fluid compartment in the body and the primary source of lymph, the authors note. Researchers have known about the “interstitium” – the tissue between organs and vessels in the body – for a long time. Examination of these samples, and subsequently a range of other tissues, identified the same architecture of fluid-filled compartments and their supporting collagen bundles and lining cells in numerous tissues and organs that move or compress. They called in the help of pathologist Neil Theise, a co-worker at the Mount Sinai hospital.

Doctors in the United States were carrying out an endoscopy on a cancer patient’s bile duct when they found that the interstitium seemed to be full of fluid-filled cavities connected by a series of channels.

LiveScience notes these discoveries are also reflected in a 2011 study, which signaled the existence of a network of dark fibers in association with several cases of bile duct cancer, but didn’t offer an explanation as to what it was.

But when the endoscopic laser was used to remove the pancreas and bile duct in a dozen patients with cancer, the odd spaces became obvious. This work has been made possible by advances in the technology we can use to look at tissue while it is still in the body. “But these were not artifacts”, Theise said.

The researchers were able to see every detail in the samples, writing that they observed where fluid accumulated in specific spaces. Indeed, the researchers plan to conduct a review of the scientific literature “for all the things we know about this [body part] but didn’t know we knew it”, Theise said.

Theise and colleagues are already investigating the developmental anatomy of the interstitium in mice, as well as looking more in depth at how it appears in other tissues in both animal models and people.

“They had been there all the time”.