MRI may be used to assist with surgical planning, such as choosing between hysterectomy and a more conservative surgery. The knowledge of the precise topography, including depth or laterality of invasion based on the MRI findings, can alter the surgical approach with regard to a need for ureteral stenting, vascular clamping, and/or embolization [3,35]. It has been suggested that MRI is particularly valuable in detecting placental invasion to parametrium [11]. Because MRI is also associated with both false-positive and false-negative diagnoses [36], the examination may be complementary to the US evaluation. The earliest recommended timing for a diagnostic quality MRI scan after a suspicious US is after 24 weeks [32]. An earlier MRI may be useful in a limited setting, such as preoperative planning for termination of the pregnancy or in the setting of severe disease for staging. Interobserver agreement has been shown to improve with extent of placental invasion [28]. At least four studies have performed direct comparison of MRI with US and found sensitivity of 93% and specificity of 94% for MRI compared with 88% and 96%, respectively, for US [37-40]. Warshak et al [20] advised a 2-stage protocol, starting with US and followed by MRI. Pregnant patients can be informed that there are no known deleterious effects on the fetus performed in 1.5T or 3.0T magnets [41]. US Duplex Doppler Pregnant Uterus The addition of Doppler imaging can improve both detection and progression of the presence of increased placental vascular flow, subplacental vascularity, and vascularity at the bladder uterine-serosal interface, with vessels seen crossing or bridging from placenta to bladder. The presence of multiple vascular lacunae in the placenta is thought to be related to the exposure to pulsatile blood flow, high-velocity blood flow from myometrium to lacunae.
Placenta Accreta Spectrum Disorder. MRI may be used to assist with surgical planning, such as choosing between hysterectomy and a more conservative surgery. The knowledge of the precise topography, including depth or laterality of invasion based on the MRI findings, can alter the surgical approach with regard to a need for ureteral stenting, vascular clamping, and/or embolization [3,35]. It has been suggested that MRI is particularly valuable in detecting placental invasion to parametrium [11]. Because MRI is also associated with both false-positive and false-negative diagnoses [36], the examination may be complementary to the US evaluation. The earliest recommended timing for a diagnostic quality MRI scan after a suspicious US is after 24 weeks [32]. An earlier MRI may be useful in a limited setting, such as preoperative planning for termination of the pregnancy or in the setting of severe disease for staging. Interobserver agreement has been shown to improve with extent of placental invasion [28]. At least four studies have performed direct comparison of MRI with US and found sensitivity of 93% and specificity of 94% for MRI compared with 88% and 96%, respectively, for US [37-40]. Warshak et al [20] advised a 2-stage protocol, starting with US and followed by MRI. Pregnant patients can be informed that there are no known deleterious effects on the fetus performed in 1.5T or 3.0T magnets [41]. US Duplex Doppler Pregnant Uterus The addition of Doppler imaging can improve both detection and progression of the presence of increased placental vascular flow, subplacental vascularity, and vascularity at the bladder uterine-serosal interface, with vessels seen crossing or bridging from placenta to bladder. The presence of multiple vascular lacunae in the placenta is thought to be related to the exposure to pulsatile blood flow, high-velocity blood flow from myometrium to lacunae.