[Pathology of small intestine transplantation]

Small bowel transplantation is being increasingly performed to treat patients with irreversible intestinal failure or short bowel syndrome. Worldwide approximately 100 transplantations are currently performed per year. Technical advances and new immunosuppressive strategies adopted during the last 10 years have significantly improved the quality of live and survival rate of the patients. The 5-year survival rate is currently around 60%. However, the procedure still bears significant live threatening risks. Mayor problems include surgical complications like anastomotic leakage or peritonitis, acute allograft rejection, systemic infection and in later stages loss of graft function due to chronic rejection. Acute rejection is common after intestinal transplantation. It may occur any time after transplantation and is seen in 50%-80% of the patients. The characteristic changes are enterocyte apoptosis in the crypts, cryptitis and mononuclear cell infiltration with activated lymphocytes. Severe cases may reveal ulcerations or even sloughing and widespread exfoliation of the epithelium and are almost invariably associated with graft loss. The histopathological abnormalities may be patchy and occur in grossly normal mucosa. Therefore, multiple biopsies should be generally sampled for histology. Acute rejection must be distinguished from infections in particular opportunistic viral infections caused by Cytomegalovirus (CMV) or Adenovirus as well as from Epstein-Barr virus-related B-lymphocyte proliferations. Differential diagnosis also includes preservation injury and ischemia resulting in damage of the mucosal surface epithelium. Long-term graft function and survival are now increasingly determined by chronic rejection. The hallmarks of chronic rejection are obliterative arteriopathy of mesenterial vessels and progressive fibrosis of the transplant including its mesentery.