**1. Introduction**

Placenta accreta, placenta increta, and placenta percreta represent a spectrum of placental adhesive disorders (PAD) and occur when a defect of the decidua basalis allows the invasion of chorionic villi into the myometrium. PAD is classified on the basis of the extent of adherence to and invasion of the myometrium. Placenta accreta is the least severe of the three entities with superficial invasion of the basalis decidua by the chorionic villi (approximately 75% of cases). Placenta increta is penetration of the myometrium by the chorionic villi, while

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

placenta percreta is the most severe with invasion of uterine serosa or adjacent pelvic organs [1, 2]. It is worth noting that when the myometrium becomes very thin especially at the level of the cesarean section, difference between accreta and increta is obsolete.

**3.** Bladder wall loss or interruption or irregularity (loss of hyperechoic band or "line" between

Placental Malformation: Accreta and Beyond http://dx.doi.org/10.5772/intechopen.80588 75

**4.** Uterovesical hypervascularity, defined as striking color Doppler signal observed between myometrium and posterior wall of bladder, including vessels bridging uterine-placental margin, across myometrium and beyond serosa into the bladder or other organs; running

**5.** Invasion of the cervix, resulting in abnormal cervical shape, cervical lacunae, and placenta

**6.** Vascular invasion of the parametria, defined as the presence of hypervascularity extending

In addition, we should emphasize on the US limitations especially regarding the difficult access to posterior placental locations, the evaluation of the degree of placental infiltration, or

MRI is a secondary diagnostic tool for AIP and indicated when US is limited and inconclusive or in cases of a posterior placenta [4, 6, 7, 10, 14]. The examination typically is made between 24 and 32 weeks of gestational age, in a supine position, but if not tolerated it can be made in left lateral decubitus or oblique position. The bladder is partially distended during the study. MRI protocol is essentially based on three-plane T2 sequences for the placental assessment (single-shot T2-weighted fast spin echo sequences or T2-weighted TSE); a T1-weighted sequence can be acquired, and recently, the utility of diffusion-weighted imaging is discussed in many studies [6]. Although contrast-enhanced imaging can improve the diagnostic accuracy of placental invasion while improving the contrast between the myometrium and the placenta, gadolinium usage during pregnancy should be avoided [6, 7]. MRI signs suggesting

**2.** Presence of dark intraplacental bands on T2-weighted imaging running perpendicular to

**4.** Uterine bulging defined as a focal outward contour or a loss of the pear shape of the uterus **5.** Direct visualization of focal exophytic mass breaking through uterine serosa and invading

**6.** Heterogeneous intraplacental signal intensity but can be a subjective sign depending on

beyond the lateral uterine walls and involving the region of the parametria

**1.** Myometrial thinning or focal interruption of the myometrium by placenta

the presence of associated myometrial lesions [4, 10, 12, 13].

uterine serosa and bladder lumen)

perpendicular to the myometrium

**2.2. Magnetic resonance imaging (MRI)**

AIP include the following [4, 6, 10, 15]:

the gestational age of the placenta

**7.** Abnormal intraplacental vascularity (**Figure 1A**-**D**)

the myometrium

pelvic structures

**3.** Tenting of the bladder

previa

The frequency of abnormal invasive placentation (AIP) has risen in the last 30 years parallel to the increase in cesarean delivery rate [3, 4]. Other common risk factors for abnormal placentation include placenta previa, prior myomectomy or other uterine surgery, and advanced maternal age [5].

AIP is a life-threatening condition due to massive hemorrhage and urgent need for blood transfusion, the need for peripartum hysterectomy, damage to adjacent organs due to placental invasion, and the need for admission to the intensive-care unit [4, 6, 7]. For these reasons and their consequence of decreasing the burden of maternal morbidity-mortality, it is essential to accurately diagnose the degree of placental invasion. The major predicting determinant of the outcome of women affected of AIP is the depth of placental invasion [3].
