Fig. 7

Haematoxylin and eosin histology. a. Low magnification image showing ablation zone (AZ) contoured with dashed yellow line. AZ encompasses muscle tissue adjacent to the SIJ. b. Boundary of the AZ corresponding to the dashed box in a. Accumulation of the macrophages at the boundary is marked with black arrows. c. Appearance of the bone surface outside of AZ, corresponding to the solid-line box (left) in b. d. Changes in the bone surface caused by HIFU. Asterisk shows the ligament at the surface of the bone. e-f. High magnification image of the regions marked with the two circles in a. Closer to the boundary of AZ the nerve exhibits hyperaemia of endoneurial vessels (think arrows), the stroma surrounding the nerve (thicker arrow) appear pink as in normal nerve. Hemorrhage in the surrounding muscle is marked with a short arrow. The artery (arrowhead) showed fibrinoid necrosis of the tunica media. In the central region of AZ (f), the nerve morphology appears unchanged, however, there is pronounced hyalinisation of the collagen in the neural stroma and the ligament tissue on the surface of the bone (asterisk) . The artery (arrowhead) shows hyalinisation of the collagen with the outer surface of the vessel appearing purple compared to pink in e. Scale bar is 50 microns