Purpose of investigation: Cesarean scar pregnancy (CSP) is a life-threatening condition that requires early pregnancy termination. Its early ultrasound diagnosis is clinically important; however, previous studies focused on the CSP site itself. The present study was conducted to investigate the authors’ clinical impression that a uterine-fundal hypoechoic mass is more frequently observed in CSP. Such a finding, if confirmed, may contribute to ultrasound diagnosis of CSP. The authors also determined the relationship between the treatment strategy and outcome, with special emphasis on conditions eventually requiring uterine artery embolization (UAE). Materials and Methods: This was a case-control study of CSP, and the authors analyzed all 14 women that were treated in this single tertiary institute over a period of ten years. Control subjects consisted of all pregnant women with prior cesarean section (CS) but no CSP. Results: Patients with CSP were significantly more likely to have a hypoechoic mass than controls (42.9 vs. 15.4%, respectively; p = 0.028). On confining results to a “fundal” hypoechoic mass, only CSP(+) patients showed it (CSP vs. control: 28.6 vs. 0%, respectively; p < 0.001). Six (43%: 6/14) received UAE: four following vaginal evacuation (artificial or spontaneous), and two for bleeding after methotrexate (MTX) treatment. Conclusion: Patients with CSP more frequently had a uterine-fundal hypoechoic mass, whose detection may trigger a detailed observation of the CSP site, possibly leading to CSP diagnosis.