Trending Science: Say hello to interstitium, what’s likely the newest organ in your body

How is it that an organ so big has gone unnoticed all these years by the scientific community? And it’s been lying beneath our skin the whole time!

A team of researchers at the New York University’s School of Medicine have identified the interstitium as an organ in its own right, and one of the largest of the body. Published in the journal ‘Scientific Reports’, this is the first study to recognise the organ as a network that runs throughout the body. Think of it as a highway of moving fluid.

Interstitium lies below the skin’s surface and between muscles, lining the digestive tract, lungs and urinary systems, and surrounding arteries and veins. The team suspects that the interconnected, fluid-filled compartments act as shock absorbers that prevent vital tissue damage in organs, muscles and vessels.

How did interstitium go undetected?

Medicine relies on traditional methods to examine body tissues. These techniques prepare the tissue by treating it with chemicals, slicing it thinly and dying it to identify key components more easily. However, this method drains fluid from the sample. Without the fluid, the compartments collapse, squishing the interstitium like a pancake and making it hard to identify.

The NYU researchers discovered interstitium by using new technology that provides a look at living tissues instead of fixed ones. They were investigating a patient’s bile duct searching for signs of cancer. Instead of the anticipated compact connective tissue, Dr Neil Theise, a pathology professor at NYU Langone Health in New York City and co-author of the study, stumbled on compartments filled with fluid. Until now, the medical field thought the squashed layer was just dense connective tissue.

Dr Theise and his fellow researchers understood that this structure was found not only in the bile duct, but surrounding many crucial internal organs. “This fixation artefact of collapse has made a fluid-filled tissue type throughout the body appear solid in biopsy slides for decades, and our results correct for this to expand the anatomy of most tissues,” he told the UK’s ‘Independent’. Discussing the accidental discovery with ‘National Geographic’, Dr Theise added: “You’re talking about the remaining extracellular fluid that’s unaccounted for. About 70 percent of the human body is made of water, and about two thirds of that is found in cells. The remaining third is only partially known.”

Biological superhighway to help treat disease

The scientists believe interstitium is a source of lymph, a fluid that moves through the body’s lymphatic system and is involved in immunity. They found evidence that cancer cells from tumours could travel through the interstitium into the lymphatic system. Understanding how diseases spread through this part of the body could help researchers become better aware of the spread of cancer.

In the ‘Independent’, Dr Theise offered the following on interstitium’s promise: “This finding has potential to drive dramatic advances in medicine, including the possibility that the direct sampling of interstitial fluid may become a powerful diagnostic tool.”