Analysis of Scars and Keloids Using a Focused Ion Beam/Scanning Electron Microscope -Differentiation between Hypertrophic Scars and Keloids-

(Background) Histological differentiation between hypertrophic scars and keloids has been considered difficult until now. In this study, we analyzed the three-dimensional structure of hypertrophic scars and keloid cells using a focused ion beam/scanning electron microscope (FIB/SEM), distinguishing them by clarifying the differences in cytoarchitecture in three dimensions.

(Methods) The subjects included five patients with normal skin, five with mature scars, five with hypertrophic scars, and five with keloids. In each case, three sites were observed by FIB/SEM, giving a number of observed sites of 3 × 5 = 15 sites per tissue, a total of 60 sites. We then observed if there was any contact between fibroblasts and macrophages along with the degree of contact (planar or point), and examined whether or not there was a significant difference between the four tissues using Fisher’s exact test.

(Results) In normal skin, contact between fibroblasts and macrophages was observed at all 15 observation sites, and the degree of contact for all was "planar contact" (100%). In mature scars, there was contact at 13 of 15 sites (87%), including 12 sites with "planar contact" (80%), 1 site with "point contact" (7%), and 2 sites with "no contact" (13%). Regarding hypertrophic scars, there was contact at 12 of 15 sites (80%), including 3 sites with "planar contacts" (20%) and 9 sites with "point contact" (60%), and 2 sites with "no contact" (20%). In keloids, there was contact at 2 of 15 sites (15%), including 1 site with "planar contact" (7.5%), 1 site with "point contact" (7.5%), and 13 sites with "no contact" (85%). Regarding whether or not there was any contact between fibroblasts and macrophages, while no significant difference was found between the three types of tissues, including normal skin, mature scars, and hypertrophic scars, there was a significant difference between the three types of tissues and keloids. Regarding the degree of contact ("planar contact" and "point contact") of cells in these three types of tissues determined to be in contact, while no significant difference was found between normal skin and mature scars, there was a significant difference between these two types of tissues and hypertrophic scars.

(Conclusion) The contact between fibroblasts and macrophages in normal skin and mature scars is "planar contact," suggesting that macrophages are able to sufficiently control the action and proliferation of fibroblasts. On the other hand, in hypertrophic scars, the contact becomes "point contact," making control unstable, while in keloids, macrophages are completely separated from the fibroblasts, with the proliferation thereof expected to be in an uncontrollable state. Therefore, keloids were suggested to be a disease in which control by macrophages is ineffective, with fibroblasts undergoing neoplastic proliferation on their own. FIB/SEM can be a useful tool for differentiating between hypertrophic scars and keloids in the future, which is considered to be an important hint in the development of therapies therefor.