Ruptured rudimentary horn pregnancy mimicking abdominal gestation: A case report.

A unicornuate uterus with a rudimentary horn, resulting from incomplete development of one of the Müllerian ducts, is a rare anomaly seen in about 0.4% of women and carries a high risk of ectopic pregnancy and uterine rupture, particularly when the horn is noncommunicating. A 27-year-old primigravida at 16 weeks' gestation presented with symptoms of hypovolemic shock and peritonitis. Abdominopelvic ultrasound demonstrated an empty uterine cavity with a viable extrauterine fetus, leading to a presumed diagnosis of abdominal pregnancy, and emergency laparotomy confirmed a ruptured pregnancy in a noncommunicating rudimentary horn with significant hemoperitoneum. Surgical removal of the horn and left fallopian tube was performed, and the patient recovered well. This case highlights a common diagnostic pitfall, as rudimentary horn pregnancy is frequently misidentified on ultrasound as an abdominal or intrauterine gestation. Recognition of key ultrasonographic features, including lack of continuity with the endometrial cavity, a myometrial mantle surrounding the gestational sac, and a vascular pedicle, may facilitate earlier diagnosis and reduce the risk of catastrophic rupture. Due to the diagnostic challenges posed by this condition, early identification using advanced imaging and prompt surgical management are critical to reducing maternal risk.