Luminal Myofibroblastic Proliferation (LMP) in KD CAA.

A. The peri-luminal portion of the CA SA/C-LMP is rich in polygonal shaped myofibroblasts, while elsewhere the myofibroblasts are more pleomorphic. The background is mostly small lymphocytes. Alpha-SMA IHC, case 18, original magnification 63×. B. At higher magnification, the myofibroblasts in this area of SA/C-LMP resemble a culture of pleomorphic mesenchymal cells. The SA/C background is especially rich in small lymphocytes. Alpha-SMA IHC, case 13, original magnification 100×. C. The LMP resembles a “syncytium” of pleomorphic MF with red-staining actin and blue-staining pro-collagen. SA/C nuclei stain dark red. There is some blue staining of the ECM. The luminal lining (top) consists of RBCs and dark red staining fibrin. Trichrome stain, case 13, original magnification 100×. D. The SA/C-LMP contains large, pleomorphic myofibroblasts with large nuclei and several small nucleoli. The ECM is difficult to delineate. Trichrome stained plastic section, case 13, original magnification 160×. L=lumen, MF=myofibroblast, LMP=luminal myofibroblastic proliferation.