In the 17th century, physician Samuel Collins observed a mesh around each organ, which he called a “common Vest” made of “curious well-spun Threads… wonderfully interwoven with each other”. The “remanent spaces”, he noted, were filled with a “concreted Animal Liquor”. Over the following centuries, the purpose of these structures was thought to be purely architectural.
The vest, known today as fascia, offers a kind of girding that holds our organs in place; the gaps filled with that “animal liquor” – called interstitial fluid – provide a kind of shock absorber that allows our organs to slide freely as we move, without bruising. We now know that those pockets of fluid are far more important than this. Emerging research suggests they form an interconnected network called the interstitium that provides an important channel of communication between and inside our tissues.
And that is set to cause a quiet revolution in medicine, changing how we think about everything from muscle pain and the microbiome to the spread of cancerous tumours across the body. According to some scientists, it may even offer a modern explanation for concepts in traditional Chinese medicine, including the fundamental life force “qi”. The interstitium’s basic anatomy certainly suggests some structural role.
The extracellular matrix within it provides structural support for pockets of fluid, with threads made of collagen, which create a strong scaffold, and elastin, which act like tiny bungee cords and offer flexibility. The interstitial fluid coursing through gaps in this matrix comprises around 12 per cent of our body weight and contains hyaluronic acid, a large molecule that forms a gel in water, perfect for cushioning delicate tissue. The mainstream view was that each organ and muscle is sealed off in its own compartment, with its own, isolated interstitium.
While a few researchers, such as molecular engineer Melody Swartz at the University of Chicago, have long been interested in how the fluid flows within the different compartments, there was little evidence that they were interconnected. That was partly due to a serious practical limitation: when you take tissue samples to study under a microscope, the interstitial fluid drains away and the collagen fibres that give the cavities their structure collapse in on themselves. This made it very hard to characterise the space.
Fascia: The long-overlooked tissue that shapes your health That changed with a groundbreaking study in 2018, using a new procedure that combines a laser with an endoscope to build microscopic images of tissue in a living body. This enabled Neil Theise, professor of pathology at the New York University Grossman School of Medicine, and his colleagues to follow the movement of a fluorescent dye injected during pancreatic surgery. This revealed a series of channels and cavities where they had expected to find dense connective tissue, suggesting that the interstitium was larger and more intricate than previously recognised.
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