Did scientists just discover a new organ called the interstitium?

You would have thought that, with all the medical technology we have nowadays, the human body wouldn’t have any surprises left in store. So, the headlines proclaiming the discovery of a new organ (called interstitium) are incredibly exciting. But dig into this story, and it gets a little trickier. This new discovery both is and is not an organ, and it seems to be something that people familiar with human anatomy are already aware of – what’s going on?

In a recently published paper in Nature, doctors proposed that the interstitium is the eightieth organ, and the biggest in the human body by volume (they don’t actually call it an organ in the paper, but they’ve referred to it that way in a number of press interviews following the discovery). Now, the human body contains something called connective tissue – broadly, it’s a class of tissues that support other tissues and organs (bone, blood, and fat are some specialised examples). This paper argues that a certain type of connective tissue forms a protective layer around other organs (acting as a ‘shock absorber’ of sorts) and that this tissue is connected within a greater network of fluid-filled spaces – the interstitium.

The human body contains something called connective tissue – broadly, it’s a class of tissues that support other tissues and organs

Now, scientists have long known that there is interstitial space in the body and that it contains fluid – the idea that this is an entirely new discovery is not right. Scientists were aware of the connective tissues (which they called the ‘interstitial lining’) but just assumed that it was a passive reservoir for fluid and a physical support system for important organs, and so they didn’t look too much further (to quote one of the researchers, “you see what you expect to see”). What has changed is the way that scientists are now able to look at the human body.

In the past, scientists would use microscopic slides to peer into the cellular world. However, after they had prepared the tissue samples for these slides (by treating them with chemicals, cutting them into thin slices and dyeing them to highlight key features), the fluid would be completely drained away. We didn’t know that this fluid-filled space existed because they could not be observed. The discovery came after scientists used a new in-vivo microscopy technique to examine living tissue – they then removed and flash froze some tissue, confirming the existence of this network.

We didn’t know that this fluid-filled space existed because they could not be observed

Technicalities over whether or not the interstitium should be considered an organ or not aside, further research could help enhance our understanding of some key medical questions. One of the scientists who made the discovery is very enthusiastic, hoping that “it would change how we understood everything from cancer to acupuncture to inflammation.” The potential relation to cancer research has excited numerous observers – it has been suggested that it could help explain why cancer tumours spread. One of the authors compared the network to a “railroad for cells” – cancer often spreads by getting into the lymphatic system and, if it can be proved that the interstitium connects to lymphatic channels, it could suggest potential new avenues for treating cancer at an early stage.

It’s always exciting when a new scientific discovery occurs, but the implications of this study are far from settled. The paper had been rejected numerous times prior to its eventual publication, so the discovery is evidently a contentious one in the scientific community. More research is needed into the interstitium, although the scientists have stated that a great deal of research and information may already be out there (they are planning to conduct a review of the scientific literature “for all the things we know about this [organ] but didn’t know we knew it”).

The potential relation to cancer research has excited numerous observers – it has been suggested that it could help explain why cancer tumours spread

For now, the interstitium will remain a key example of not taking knowledge for granted, but many eyes will be on this strange discovery-non-discovery hybrid to see if it turns out to be much more and whether it can truly provide some of the medical breakthroughs being suggested of it.