A and B: Submucosal vessels of intestinal resection specimens pre- and post-eculizumab, respectively. There were a total of 3 intestinal resection specimens available for assessment. One was obtained prior to the commencement of the drug (July 2009) and two were obtained 4 months (February 2010) and 21 months after starting the drug (July 2011). There are aspects of the pathology that was remarkably similar between the pre-eculizumab specimen and the one obtained 2 years after starting therapy. A striking fibro-obliterative arteriopathy affects small and medium-sized vessels of the submucosa as well as mesentery in both the pre- (A) and post-treatment (B) resection specimens (3A, hematoxylin and eosin, 200x, 3B hematoxylin and eosin, 200x). In B, the intimal proliferative changes are very striking comprising hypercellularity of the intima along with an increase in intimal matrix represented by collagen and hyaluronic acid.