Abnormal placentation: MRI evaluation
Type:Educational Electronic Presentation
Authors: André Peixoto
Keywords:Abnormal placentation; placenta accreta
Educational objective

To review abnormal placentation: placenta accreta, increta, and percreta

To review MRI protocol

To describe imaging features

To evaluate and illustrate placental invasiveness

Topic Review

Abnormal placentation: placenta accreta, increta, and percreta


The frequency of abnormal placentation, such as placenta accreta, is increasing.

Placenta accreta consists of a defective decidualization of the implantation site resulting in an abnormal invasion of the myometrium by chorionic villi.

Depending on the depth of placental invasion it can be classified as accreta, increta, or percreta.

In the placenta accrete villi are attached to the myometrium but do not invade the muscle, it is the mildest form. In the placenta increta, villi partially invade the myometrium. In the placenta percreta, it penetrates through the serosa and could invade other organs.

At the delivery, abnormal placentation can cause massive hemorrhage and severe consequences such as disseminated intravascular coagulopathy, adult respiratory...

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Fig. 1) Placenta previa. Sagittal T2-weighted images: placenta previa without signs of placenta accreta.
Fig. 2) Placenta increta - Sagittal TSE T2-weighted images: inferior bulging of the uterus (solid white arrow) as well as severe thinning and interruption of the normal three-layered appearance of the myometrium (outer layer: dashed white arrow; middle layer: white cardinal; inner layer: dashed black arrow). Dark intraplacental bands were also noticed in the expected region of the previous cesarean section scar (white asterisk).


Abnormal placentation can lead to life-threatening hemorrhage. It is also an important cause of emergent hysterectomy during childbirth.

A multidisciplinary team is necessary to reduce morbidity and mortality.

Ultrasound and MRI are important exams for diagnosis, evaluation, and planning of the delivery.

MRI is particularly useful when ultrasound examination is inconclusive or incomplete.

The most useful findings in abnormal placentation are heterogeneous signal intensity within the placenta, dark placental bands on T2-weighted images, and uterine bulging.