Evidence of interstitial continuity within and beyond the human pancreas

Bodies have continuous reticular networks, comprising collagens and other extracellular matrix components, through all tissues and organs. We recently validated fluid flow through human interstitium and demonstrated that they are filled with hyaluronic acid by staining with biotinylated hyaluronic acid binding protein. Their continuity across tissue boundaries (skin and subcutis), and between organs (colon and mesentery) and along vessels (within adventitia) and nerves (within perineurium) has been demonstrated in this manner. We aim to evaluate the continuity of interstitium within human pancreas and beyond into adjoining tissues. Tissue blocks of histologically normal pancreas from nine pancreatectomy specimens were sectioned in parallel for staining with hematoxylin and eosin, Picrosirius red, and biotinylated hyaluronic acid binding protein. Also, specimens of invasive pancreatic cancer were assessed for interstitial tumor invasion. Picrosirius red ensheathes all microscopic units of the endocrine and exocrine pancreas, including acini, islets, and ducts, adventitia of blood vessels and perineurium, and into adjacent duodenum. Interstitial spaces within the fibrous tissue are filled with hyaluronic acid by staining and are also continuous through all microscopic structures of the pancreas, into adjoining duodenum and along vessels (within adventitia) and nerves (within perineurium). Invasive carcinoma is seen spreading through pre-existing interstitial spaces. Interstitium of the human pancreas is continuous within and beyond the pancreas. This continuity suggests the capacity to be a route of molecular, microbiome, and cellular trafficking and communication. In particular, it is a route of cancer spread.