Deciduosis of the appendix.

A clinicopathologic and immunohistochemical study of six cases of deciduosis of the appendix is presented. The patients were pregnant women aged 18-40 years. In four cases, the patients presented with signs and symptoms of acute appendicitis during their 26th to 31st week of pregnancy; in the other two, the lesions were discovered incidentally in appendectomy specimens obtained during cesarean section and tubal ligation at term. Histologically, the lesions were characterized by the presence of multiple, irregularly distributed submesothelial deposits of decidualized cells in the serosa of the appendix, without any associated evidence of endometriosis. By immunohistochemistry, the decidualized cells strongly labelled with vimentin antibodies, consistent with their stromal origin. In two cases, coexpression of vimentin and desmin intermediate filaments was observed, suggestive of myoid differentiation. The possible relationship of the lesions with the development of symptoms of peritoneal irritation in these patients is discussed along with a review of the literature on the abdominal complications of ectopic decidua.