Using probe-based confocal laser endomicroscopy (pCLE), researchers can now view living tissue at the microscopic level—leading to the recent discovery of fluid-filled spaces in the body's connective tissue. In a recently published report, investigators are calling the interconnected, fluid-filled spaces supported by a lattice of thick collagen "bundles" a new “organ,” although further research and a consensus is necessary before the label can become official.1

Previous research used standard microscopic slides to explore this tissue layer, which, when viewed on the slides, appeared to be “densely-packed barrier-like walls of collagen.”2 pCLE reveals a failing of this traditional scientific method, as the preparation process collapsed the fluid-filled spaces and hid them from examination for decades, the researchers said in the report. By viewing the live tissue, Neil Theise, MD, a professor of pathology at New York University Langone School of Medicine, and colleagues found not a dense structure, but an "open, fluid-filled highway," that transports “interstitial" fluid, including lymph and drains into the lymphatic system.1

Because the purported new “organ” is in connective tissues all over the body, the researchers hypothesize several functions—and possible dysfunctions. For one, they note the interstitium may act as a “shock absorber” for other organs subject to “cycles of compression and distension.”2 And because it seems integral to lymph movement throughout the body, it may also be “a potential conduit for movement of injurious agents, pro-fibrogenic signaling molecules, and tumor cells,” according to the study. “This raises the possibility that direct sampling of the interstitial fluid could be a diagnostic tool.”

This finding, while potentially ground-breaking, raises more questions than it answers. However, it "allows us ask all kinds of questions we didn't even know to ask beforehand," said Michael Nathanson, MD, chief of the digestive diseases section at Yale University School of Medicine, who was not involved in the work but observed the network of dark fibers in a 2011 study of his own.1

1. Rettner R. Meet your interstitium, a newfound 'organ.' Live Science. March 27, 2018. Accessed March 29, 2018.
2. Benias PC, Wells RG, Sackey-Aboagye  B, et al. Structure and distribution of an unrecognized interstitium in human tissues. Scientific Reports 2018;8:4947.