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Scientific Session 10 — SS10: Genitourinary Imaging - Female Pelvis/Endocrine

Tuesday, May 7, 2019

Abstracts 1920-2889

1920. Placental Bulge as a Predictor for Myometrial Invasion in Prenatal Diagnosis of Placenta Accreta Spectrum Disorder

Jha P*,  Rabban J,  Li B,  Chen L,  Poder L. University of California - San Francisco, San Francisco, CA

Address correspondence to P. Jha (

Objective: To evaluate the correlation of “placental bulge sign” with depth of invasion in patients with placenta accreta spectrum. Placental bulge sign is defined as deviation of uterine serosa from expected plane caused by abnormal outward bulge of placental tissue.

Materials and Methods: In this HIPAA-compliant, IRB-approved, retrospective study, patients undergoing MR imaging for evaluation of placenta accreta spectrum between March 2015 and 2018 were included. Patients who delivered elsewhere were excluded. Evaluation for placental bulge was performed by 2 independent readers. Surgical pathology from cesarean hysterectomy or pathology of the delivered placenta was used as a reference standard. Statistical significance was calculated with chi-square test, and interreader agreement was evaluated with kappa analysis.

Results: Over 3 years, 61 patients underwent MRI for invasive placenta. Three patients delivered elsewhere and were excluded; 17 cases were normal placenta. At surgical pathology from cesarean hysterectomy, there were 8 cases of placenta accreta, 29 increta, and 4 percreta. Placental bulge was present in 32 of 33 increta and percreta cases (true positive= 96.9%). Placental bulge was absent in 25 of 26 cases of normal placenta or placenta accreta without myometrial invasion (true negative=96.2%). Positive and negative predictive values were 96.9% and 96.2%, respectively. The results were statistically significant (p<0.01). Estimated kappa of 0.87 signified excellent interreader concordance. In one false-positive, placenta itself was normal, but the bulge was present. On surgical pathology, this patient has markedly thinned, fibrotic myometrium without accreta. One false-negative case was imaged at 16 weeks and may have been too early to diagnose the placental bulge sign.

Conclusion: Presence of uterine bulge signifies placental myometrial invasion and at least placenta increta. In conjunction with other findings of invasive placenta, placental bulge was 100% predictive of myometrial invasion. Using the bulge alone without other signs can lead to false-positive results.