Acute abdominal pain in the third trimester of pregnancy caused by adnexal torsion based on a small cystic adenoma

A 25-year-old woman presented in the third trimester of pregnancy with severe abdominal pain in the lower right abdominal quadrant. Differential diagnosis included urolithiasis, adnexal torsion and appendicitis. A definitive diagnosis could not be made based on clinical and laboratory examination. Ultrasonography revealed a 3-cm cyst in the lower right abdomen, which was considered unlikely to cause abdominal pain. During laparotomy, adnexal torsion was found, which was deemed to be the cause of the abdominal pain. The twisted portion was uncoiled and the dark-coloured cyst was extirpated. The cyst was determined to be a cystic adenoma. Adnexal torsion is rarely caused by cysts smaller than 5 cm, especially in the third trimester. Emergency laparoscopyllaparotomy should be performed if adnexal torsion is suspected to confirm the diagnosis and uncoil the twist to prevent ovarian damage. Adnexal torsion should be considered in the differential diagnosis of acute abdominal pain in the third trimester of pregnancy.