Novel MRI finding for diagnosis of invasive placenta praevia: evaluation of findings for 65 patients using clinical and histopathological correlations

To review established magnetic resonance (MR) criteria and describe a new MR finding for the diagnosis of invasive placenta praevia. A retrospective review of prenatal MRI examinations of 65 patients (median age: 35 years) who underwent MR for the screening of invasive placenta praevia. All MRIs were performed on a 1.5-T unit, including axial, coronal and sagittal T2-weighted half-Fourier single-shot turbo spin echo imaging. Fifteen patients were diagnosed with invasive placenta praevia. Two experienced radiologists reviewed the MR images and evaluated a total of six MRI features of the placenta, including our novel finding of the placental protrusion into the internal os (placental protrusion sign). Inter-rater reliability was assessed by using kappa statistics. Features with a kappa statistic > 0.40 were evaluated using Fisher's two-sided exact test for comparison of their capabilities for placental invasion assessment. Interobserver reliability was moderate or better for the intraplacental T2 dark band, intraplacental abnormal vascularity, uterine bulging, heterogeneous placenta and placental protrusion sign. Fisher's two-sided exact test results showed all these features were significantly associated with invasive placenta praevia. The novel MRI finding of a placental protrusion sign is a useful addition to the established MRI findings for the diagnosis of invasive placenta praevia. aEuro cent Prenatal diagnosis for an invasive placenta is essential for perinatal planning. aEuro cent Magnetic resonance imaging provides useful information for the diagnosis of invasive placenta. aEuro cent The placental protrusion sign is a useful novel MRI finding for predicting invasive placenta.