[A pregnant woman with abdominal pain and fever]

Ectopic deciduosis is most often located in the ovaries, cervix and uterus, but can also be located on peritoneal surfaces of pelvic- and abdominal organs. The findings from surgical biopsies taken during pregnancy are mostly asymptomatic and incidental. Deciduosis of the appendix is rare, but it is a known differential diagnosis to acute appendicitis in pregnancy. We report a 27-year-old woman, Gravida 1, Para 0 in gestational week 35, who presented with acute right abdominal pain. She underwent an acute caesarean section for possible abruptio placentae. Acute appendicitis was a differential diagnosis. Peroperative findings revealed an inflamed and enlarged appendix suspicious for tumour. A pathological examination of the appendix showed decidual changes through the entire wall without signs of appendiceal endometriosis. In conclusion, symptomatic ectopic deciduosis in pregnancy is rare and may imitate acute appendicitis. This is an important differential diagnosis in pregnant women with tumour-suspect findings.