Aside from this bold claim, the scientists went one step further, suggesting the interstitium is also the largest organ in the body by volume.
"Now, it's clear that by looking in the living tissue at the microscopic level with this new confocal laser endomicroscopy ... that space is fully expanded and filled with fluid", NY professor of pathology and study co-author Dr Neil Theise said.
Published March 27 in Scientific Reports, a new study co-led by an NYU School of Medicine pathologist reveals that layers of the body long thought to be dense, connective tissues - below the skin's surface, lining the digestive tract, lungs and urinary systems, and surrounding arteries, veins, and the fascia between muscles - are instead interconnected, fluid-filled compartments.
These compartments are supported by a network of strong connective tissue proteins (collagen) and flexible ones (elastin) and can act as shock absorbers that prevent tissues from tearing as organs, muscles, and vessels are compressed, pump or beat.
Scientists in the United States have identified a new human organ hiding in plain sight, in a discovery they hope will help understand how cancer spreads within the human body. This means that cancer cells could potentially be released by the interstitium as it transports fluid throughout the body.
Theise suspects the sampling procedure used to make slides, previously the only way for scientists to inspect the tissue in detail, did change the specimens' shape.
Co-authors of the study David Carr-Locke and Petros Constantinos Benias have first encountered interstitium in 2015 while they investigate a bile duct from a cancer patient. The new study, he said, expands the concept of the interstitium by showing these structured, fluid-filled spaces within tissues, and is the first to define the interstitium as an organ in and of itself.
The system drains into the lymphatic system, and is said to be the source of lymph, which is vital to the functioning of inflammation-causing immune cells. 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.
Theise and his colleagues made use of a power microscope and a technique called confocal laser endomicroscopy to closely examine healthy living tissue samples taken from human bile ducts.
They found that the "strings" of the net contained collagen, a protein which acts as a kind of scaffolding around the pockets of fluid.
Its true nature was realised during a routine endoscopy looking at a patient's bile duct. 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. They also found evidence from some of their samples that cancer cells could get into the interstitium and move around. "This more detailed characterisation of this sub region of the body may open up new areas for better understanding of some diseases and indeed the movement and spread (metastasis) of cancer cells".
Scientists are already studying whether analyzing the fluid in the new organ can allow for more early diagnosis of cancer.