MRI as an aid to ultrasound in detecting bladder or parametrial invasion in accreta spectrum

Abstract

Ultrasonography (US) is used for screening and diagnosis of placenta accreta spectrum (PAS) . Magnetic resonance imaging (MRI) has become an aid in confirmation. Our objective was to determine whether there is utility in MRI to detect findings such as parametrial invasion and bladder invasion in women with suspected PAS by ultrasound. We performed a retrospective cohort study of 62 people who underwent a hysterectomy for the management of PAS in a tertiary hospital system. MRI was used only after PAS was suspected by ultrasound. US, MRI, operative and pathology reports were reviewed for the presence or absence of bladder and/or parametrial invasion. Parametrial invasion was defined as extension of the placenta into the lateral pelvic side walls. Data were analyzed, with the reference gold standard being operative findings, using ROC area under the curve, sensitivity, specificity, positive predictive value and negative predictive value. From the study population, 8 people had suspected bladder invasion by US and none with suspected parametrial invasion. Whereas MRI suspected bladder invasion in 12 people and 8 had suspected parametrial invasion. At the time of surgery, bladder involvement was identified in 8 people and parametrial invasion was identified in 2 people. The performance of both MRI and US were similar for bladder involvement with a fair ROC-AUC (Table 1). The imaging modalities together had similar sensitivities except that of US in detecting parametrial involvement. The performance of MRI was better than US at identification for parametrial involvement due to the difficulty in identifying parametrial involvement on US alone. Table 2 compares the agreement of MRI vs. US on bladder and parametrial invasion. In a tertiary care center, among those with suspected PAS by US, the overall addition of MRI to detect the severity, as well as bladder invasion and/or parametrial invasion, has a low detection rate with a high false positive rate.View Large Image Figure ViewerDownload Hi-res image Download (PPT)