From: Collins SL, Ashcroft A, Braun T, Calda P, Langhoff-Roos J, Morel O, et al. Proposal for standardized ultrasound descriptors of abnormally invasive placenta (AIP). Ultrasound Obstet Gynecol. 2016;47(3):271-5.
This represents the absence of sufficient myometrial tissue to support the placenta in the usual plane and hence is useful in both raising prenatal suspicion of PAS and planning management of the case. If there is a bulge, there will not be enough residual muscle to contract and provide the living ligature required to stop placental bed bleeding. Forced removal of the placenta should not be attempted if there is a bulge as it will result in uterine rupture and/or significant bleeding.
Simple Uterine Dehiscence
Occasionally, a placental bulge will be a simple uterine dehiscence (see below). In this case the placenta will lack any other signs for PAS and the bulge will usually be small and discrete. In these cases the defect will be discrete and obvious at laparotomy with no neovascularity. The defect will need excising but the placenta should separate from the surrounding myometrium.