Background Adnexal torsion complicated by small bowel volvulus (SBV) during pregnancy is a rare and potentially serious cause of acute abdomen. Its clinical presentation is complex, diagnosis can be challenging, and delayed management may compromise maternal and fetal safety. This report examines the clinical and imaging features of this condition and analyzes previously published cases to improve understanding of this uncommon entity. Case presentation  We report a patient in late pregnancy with a previously identified right adnexal teratoma who presented with right lower abdominal pain and diarrhea. The symptoms initially improved but progressively worsened within 24 hours. Serial ultrasonographic examinations demonstrated a reduction in the anteroposterior diameter of the right adnexal mass, decreased cystic components, and progressive flattening. Computed tomography revealed a mesenteric vascular whirl sign. Emergency surgery revealed four rotations of the right ovarian pedicle with dark discoloration and a flattened appearance, together with approximately 40 mL of pale-yellow purulent ascites. A 180° torsion at the root of the small bowel mesentery was also identified. After detorsion, bowel peristalsis was present, and no obvious ischemia was observed. Marked small bowel dilatation was noted from approximately 20 cm distal to the sigmoid colon to the ileocecal region, and enterotomy with decompression was performed. At the 6-week follow-up, both the mother and the infant were well. Conclusions Small bowel volvulus during pregnancy is rare, yet its clinical course may progress rapidly and potentially endanger maternal and fetal health. Ultrasonography serves as an important initial screening modality for acute abdominal pain in pregnancy; however, when mechanical obstruction or volvulus is strongly suspected, sonographic findings may lack specificity, and further evaluation with MRI or CT should be considered to avoid missed diagnosis. Diagnosis and management require careful integration of imaging findings and clinical presentation, and early surgical intervention should be undertaken when indicated to improve outcomes.