IgG4 related sclerosing encapsulating peritonitis with cocoon formation: An unusual and undescribed presentation.

IgG4-related sclerosing mesenteritis is a rare disease of mesentery of an unknown etiology which shows a constellation of histopathologic findings of lymphoplasmacytic inflammation with IgG4-positive plasma cells and marked fibrosis. This chronic inflammatory condition of mesentery forming an abdominal cocoon has never been described before to the best of our knowledge. Here, we report a patient with a history of subacute small bowel obstruction who was found to have an intra-abdominal encapsulating mass in the right iliac fossa and was finally diagnosed as IgG4-related sclerosing encapsulating peritonitis (abdominal cocoon) based on peroperative findings, histology and immunohistochemistry.