Your interstitium: an “organ” you didn’t know you had

A couple of years ago--but just recently reported--some scientists were using a new type of microscope to examine patients’ bile ducts, looking for the spread of cancer. The microscope is a type that is inserted into the body and allows scientists to examine living tissue rather than wait for the preparation of slides. In checking out the bile ducts, the scientists were surprised to discover that the tissue appeared as a fluid-filled, net-like pattern that did not correspond to any previously described anatomical structure. Even though scientists had looked at slides of this tissue for years, what they’d seen was the result of a slide-preparation process that collapses the lattice-work and removes the water. The tissue just looks crackly and dense.

Now, seeing the structure in vivo, scientists could see what they described as “a series of spaces,” and a “highway of moving fluid.” The scientific paper that described the “organ” called it a “widespread, macroscopic, fluid-filled space within and between tissues.” It is referred to as the interstitium (pronounced inter-STISH-um). It’s found all over our bodies—in or near lungs, skin, digestive tracts, and arteries. In the images, it looks fluid—something that ebbs and flows like the ocean. It may act as a shock absorber, or a conduit for fluids to enter the lymphatic system.

At the moment, there’s plenty of disagreement on whether the insterstitium can be considered an organ. But it can be considered, as one scientist called it, “an entire system that is interfacing between the vascular system and the lymphatic.” For this reason, a study of this system could give scientists a better understanding of how cancer metastasizes. As one pathologist noted, “we’ve never understood the mechanism of how that happens.” All agree that more study of the interstitium could lead to breakthroughs in cancer treatment.

Now we must wait and see and see what happens, including whether the interstitium can be considered an organ. In the meantime, you can practice pronouncing it.

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