Mid-trimester Cervico-Isthmic Pregnancy With Placenta Accreta Spectrum Mimicking Placenta Previa and Cesarean Scar Pregnancy: A Diagnostic Imaging Pitfall.

Cervico-isthmic pregnancy is a rare form of lower uterine implantation associated with a high risk of massive hemorrhage and placenta accreta spectrum (PAS), particularly when diagnosis is delayed. We report a woman in her 30s with a history of cesarean delivery who was referred at 19 weeks' gestation with recurrent vaginal bleeding; no first-trimester imaging had been performed. Initial ultrasonography suggested marginal placenta previa, whereas subsequent magnetic resonance imaging (MRI) raised concern for cesarean scar pregnancy (CSP). However, careful imaging reassessment revealed misidentification of the cervical canal, with marked shortening of the true cervix and distension of the lower uterine segment, leading to a diagnosis of cervico-isthmic pregnancy. At 20 weeks, the patient developed a sudden massive hemorrhage requiring emergency hysterectomy. Histopathology confirmed cervical stromal implantation with PAS. This case highlights the diagnostic pitfalls of mid-trimester lower uterine implantation disorders and underscores the importance of early imaging and careful reassessment of the cervical canal.