Last week I heard on Radio 4 no less, that a group of researchers announced the discovery of a new organ, they’ve named this organ the interstitium. When I listened to this, I thought to myself, how many other Radio 4 listeners felt as though the word “organ” had just been thrown into spice the story up a little. Don’t get me a wrong I trust most things I hear on Radio 4, being an avid listener I have come to trust Radio 4 as a reliable source of news, but I certainly don’t recommend it for forming a firm scientific opinion. I’m also a little sceptical when sensational claims are made, I honestly think a healthy dose of scepticism is good for scientific thinking.
I always understood the interstitium as a fluid-filled extracellular space between cells. This group of researchers have published findings that claim the existence of a compartment filled with lymph fluid and supported by a network of collagen. They state this exists throughout many tissues of the body and this compartment communicates with lymph nodes and may explain one mechanism of how cancers metastasise.
To understand their findings, I thought it would be a good idea to look at the original paper. The research was published (online 27/03/2018) in Scientific Reports, a subsidiary publication of Nature. The original study was conducted in 2012/13; the research team was looking at using a novel laser-based endoscopic probe (confocal laser endomicroscopy) to look for cholangiocarcinoma (bile duct cancer). This probe permits real-time histological analysis of tissue in vivo to a depth of 60-70 micrometres, after fluorescein injection. Instead of finding cancer cells, they identified a reticular pattern throughout the submucosa, which they were unable to correlate to any known histological feature. Initially, they thought this was peculiar to one patient, but found the same submucosal architecture in other patients, Biopsy samples were sent to a pathologist to review, but under microscopy, the reticular patterns they’d seen were not visible. They wondered whether the fixing process for microscopy preparation was causing these reticular structures to collapse, due to the specimens being dehydrated. Therefore they opted to freeze the biopsy tissue samples immediately before fixation; this time the arrangements seen on confocal laser endoscopy were visible in the lab on microscopy. This would certainly make it less likely that the pattern being recognised was an artefact created by the laser probe itself.
In my opinion, It appears what they actually have discovered, is that the process of tissue fixation for microscopy alters the histological appearance of connective tissue. In vivo, the tissue is in a hydrated state and instead of densely packed collagen, it appears as a lattice of collagen with fluid-filled spaces in between. The fact that this fluid communicates with lymph nodes, isn’t new knowledge. Even I remember being taught that interstitial fluid formed in capillary beds, bathes cells and eventually drains in to lymph vessels and nodes. What I believe they have contributed is a novel description of the architecture of the interstitium.
The medical profession has been particularly neglectful of fascia and connective tissue for decades, but that doesn’t mean all other scientists are. It will be interesting to see what the next Fascia Research Congress in Berlin will make of it, I know a good friend who will be attending, and I’ll make sure I get some feedback from him.
So do I need a new histology book? The short answer is no, so don’t go throwing out your latest edition of Junqueira’s or Wheater’s. The basis of any good scientific experiment is reproducibility. Other research groups will need to verify the group’s findings, and even then I’m sceptical of the claim that this fluid-filled cavity can now be called an organ, I mean along the same lines are the pleural and peritoneal spaces organs? I think what the research has done is highlight how the fixing process affects histological appearance and given us an insight into the architecture of this space. The research has also posed important questions regarding the shock absorbing properties of this tissue, the need to reconsider how tumours metastasise through this space and also how this fluid filled space could be used for diagnostic purposes, this may help us detect early signs of metastasis or even inflammatory processes associated with infection and autoimmune disease.
- Structure and distribution of an unrecognised interstitium in human tissues, Benias et al