1104: Pannus sign on ultrasound and MRI predicts placenta percreta

Easily obtained, objective markers of the more severe forms (FIGO class 4-6) of placenta accreta spectrum (PAS) are key to improving antenatal detection. We noted that in PAS, the placenta bulges over the cervical os. The extent of this “pannus” can be measured on ultrasound (US) and magnetic resonance imaging (MRI). We predicted that a positive sign can differentiate between percreta (Class 4-6) and generalized accreta (Class 1-3). Retrospective chart review of a database of patients with PAS from Jan 2012-Jun 2019. Demographic, clinical data and imaging data were abstracted. US and MRI images were reviewed and measured by a single researcher blinded to clinical data. The pannus sign was measured in sagittal plane (Figure, Panel A, US; Panel B, MRI). The pannus measurement (PM) is drawn parallel to the cervical canal from the most caudal placental point to the internal os line (IOL, perpendicular to and at the level of the internal os). It is the “pannus,” when positive, measured in mm. Negative (-) values indicate placenta at or cephalad to the IOL. Sensitivity, specificity, PPV and NPV were calculated using the X2 test. Of 164 women who had pathology proven PAS, 131 had adequate images, of which 120 had US, 54 had MRI and 43 had both. One with fundal PAS was excluded. 90 women had a (+) value, and 30 a (–) value on US. MR agreed with US in all but 4 cases (91%, mean difference 7.4mm.) The sensitivity and specificity were: 82.7% [95% CI, 72.5-89.6%] & 37.7% [95% CI, 25.1-77.5%] with a PPV of 68.9 and NPV of 57%. A positive PM on US was associated with hysterectomy and need for urinary tract repair, but only with hysterectomy when seen on MRI. A positive pannus sign is sensitive for percreta into bladder, but not specific; cases of parametrial or high invasion will not be detected using this sign. There is excellent agreement between US and MRI measurements, and it was easily obtained when the cervical canal could be seen. Studies of reproducibility and use with other markers of PAS are needed.