Time to re-think human anatomy: a new 'organ' has been found

A newly identified human organ called the interstitium is a fluid-filled highway of interconnected tissue throughout the body.
The interstitium is seen here beneath the top layer of skin (Jill Gregory)
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The interstitium

What scientists thought to be a layer of dense connective tissue in various parts of the human body has now been identified as something a lot more interesting: a discrete organ, the interstitum. 

It performs a previously unrecognized function in the human body — and may play an unexpected role in some diseases, including cancer.

This tissue is found below the surface of the skin, lining the digestive tract, the lungs, and urinary system, as well as surrounding arteries, veins, and the fascia between muscles.

New imaging techniques have revealed it as a series of fluid-filled spaces supported by a meshwork of collagen. It is called the interstitium because it contains the previously known interstitial fluid, which occupies the spaces in the tissue.  

How it was identified

The fluid-filled spaces in the network were previously missed because of the traditional way researchers study tissues: as thin slices of on slides for microscopes.

Although the microscope does allow scientists to see vivid details of cells and structures, it causes the fluid to drain away as the meshwork tissue collapses, making it impossible to observe the fluid-filled spaces. 

Using new technology, called probe based laser endomicroscopy, Dr. Neil Theise, a professor of pathology in the School of Medicine at New York University, was able to see the fluid-filled compartments in the tissue.

When he and his colleagues determined that these compartments exist throughout the interconnected tissue, they realized that what they found could and should be recognized as a single organ.

The interstitium and cancer

Understanding how this organ works may have implications for cancer research. One of the big puzzles has always been how it spreads through what was thought to be dense tissue. 

But this new understanding of the interstitium could help explain how cancer cells shed by tumours move so easily to the lymph nodes.

The scientists now hypothesize that cancer can travel by way of this fluid highway through the interstitium into the lymph nodes.