Neovascularisation

In-growth of blood-vessels into previously avascular areas. It occurs as a response to hypoxia in the tissues, which is a common consequence of the inflammatory response. Inflammation is associated with the accumulation of fluid and a loose web of connective tissue around the target tissue, which then facilitates increased immune-cell migration from the humoral system (blood and lymph). Increased presence of active leucocytes and radial expansion of the extracellular space associated with the inflammatory response, causes a drop in tissue gas- and nutrient-exchange. The body then naturally responds by trying to increase capillary penetration and density to meet these changed demands. This response is chiefly mediated by vascular endothelial growth-factor (VEGF). In short, neovascularisation probably acts to negate the hypoxic consequence of inflammation on parenchymal cells.

Supporting Evidence

• Oedema may increase diffusion distance from the capillaries to end tissues causing hypoxia ¹⁾https://journals.sagepub.com/doi/10.1177/026835559000500403
• Hypoxia is a confirmed trigger of angiogenesis²⁾https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3411127/
• Synovitis lowers synovial nutrient perfusion and is connected with neovessle-formation³⁾https://www.hh.um.es/pdf/Vol_16/16_1/Vasculature%20of%20the%20normal%20and%20arthritic%20synovial%20joint.pdf
• Angiogenesis counters the hypoxic effect of inflammation.⁴⁾https://www.ncbi.nlm.nih.gov/pubmed/2730714

Conflicting Evidence

• Neo-vessels may form to assist inflammation rather than as a reaction to hypoxia⁵⁾https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3886507

Association with disease

• Common finding in TP associated with increased levels of VEGF.⁶⁾https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4650849/⁷⁾https://www.ncbi.nlm.nih.gov/pubmed/31093655
• Evident in synovial tissues in OA and RA⁸⁾https://www.tandfonline.com/doi/pdf/10.3109/17453679409155226⁹⁾https://arthritis-research.biomedcentral.com/articles/10.1186/s13075-017-1229-9¹⁰⁾https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0203607
• Increased level of neovascularisation in spinal DH, related to level of histological degeneration¹¹⁾https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3886507/
• Neovascularisation is shown to occur in atherosclerosis coming from vasa vasorum¹²⁾https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3492120/
• Evidence of vascular remodelling and higher blood-flow scores in focal MPS.¹³⁾https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3493167/¹⁴⁾https://www.ncbi.nlm.nih.gov/pubmed/19887205/