Table 4.

MRI sign definitions for PAS disorders.

MRI findings	IS-AIP definition	Sequence type
Heterogeneous placenta	Heterogeneous signal within the placenta	T2W and T1W
Placental bulge	Deviation of the uterine serosa from the expected plane caused by abnormal bulge of placental tissue into neighboring organs (typically the bladder). Uterine serosa appears intact, but outline shape is distorted	T2W and T1W
Dark intraplacental bands	One or more areas of hypointensity with a linear appearance, in contact with the maternal surface of the placenta	T2W
Placental ischemic infarction	Areas of increased signal intensity (T2W) and decreased signal intensity (T1W)	T2W and T1W
Loss of the retroplacental dark zone	Loss of the thin dark zone lying beneath the placental bed	T2W
Myometrial thinning	Thinning of the myometrium overlying the placenta to less than 1 mm or invisible	T2W
Bladder wall interruption	Irregularity or disruption of the normal hypointense urinary bladder wall	T2W
Focal exophytic mass	Placental tissue seen protruding through the uterine wall and extending beyond it. Most often seen inside a filled urinary bladder	T2W and T1W
Placental bed abnormal vascularization	Large vessels within the placental bed with disruption of the uteroplacental interface	T2W

From Morel et al. [70] with permission.