An organ that’s always been hidden under the skin but never noticed may have just been discovered by scientists using new examination techniques.

A group of researchers claim to have found a new organ, the interstitium, in a study they published in Scientific Reports on Tuesday, March 27, 2018. Having previously remained unfound, the newly discovered interstitium could be the largest organ in the body and the key to discovering the solution to many diseases.

The interstitium, once considered to be a layer of dense connective tissue, is actually an interlaced web of thick and flexible connective tissue fibers filled with sacs of fluid called interstitial fluid, says NYU Langone Health. The complex of fibers serves as the connection between the lymphatic system (the system that helps the body rid itself of toxins) and the vascular system (the system that pumps oxygen and nutrients as blood through the body).

The new organ lines the inner and outer layers of the lungs, the skin, the digestive tract, and the arteries of the body. The researchers who discovered the interstitium hypothesize that it acts as a cushion or a shock absorber to the demanding functions of organs and muscles on the body. The interstitium is so large that the researchers think it may be where most of the body’s fluid is found, according to NYU.

This organ, however, has remained unnoticed by scientists looking for it for years. According to The New York Times, its discovery began back in 2014 when gastroenterology experts and endoscopists Petros Benias and David Carr-Locke used a new technique to examine their patients’ bile ducts. In the past, the only way to examine microscopic cells was through “fixing” a slide to be looked at under a microscope.

The process of “fixing” a slide involves dehydrating a tissue sample, thinly slicing it, and dyeing it to reveal the key features of the cells. Once all of this is complete, biologists place the cells onto a slide and look at it under a microscope. By drying out the tissue from the interstitium, biologists unintentionally flattened out the lattice structure of the organ for years.

However, by using the technique used by Benias and Carr-Locke, researchers are now able to see the interstitium while it is still in the body. The technique, called probe-based confocal laser endomicroscopy involves placing a thin camera attached probe down a patient’s throat. Once in the body, a laser lights up the surrounding tissue with fluorescent lighting. From there, a sensor analyzes the pattern of lighting against the cells. Through using this technique, biologists are able to view living cells rather than just fixed ones.

The scientists who discovered the interstitium used the probe-based examination by looking at the pancreas and bile ducts of 12 cancer patients, according to NYU Langone Health. The new tool allowed them to see the interstitium in action, moving and compressing around the organs.

The newly discovered interstitium could possibly help researchers diagnose health problems through examining interstitial fluid. The interstitium is a connected pathway of channels through which all of the body’s fluids flow, which may help to explain why cancer is able to spread so quickly, according to NYU Langone Health. They also added that these cells change with age and may contribute to bodily changes like “the wrinkling of skin, the stiffening of limbs, and the progression of fibrotic, sclerotic, and inflammatory diseases.”

While not all researchers agree as to whether or not the tissue is an organ, says The New York Times, it is fairly agreed upon that the new discovery will change the way doctors and researchers are able to look at the human body.