Imaging of the placenta
Number:28ESURABS0113
Type:Educational Electronic Presentation
Authors: Christopher Page, Ioanna Papadopoulou, Sara Zafar, Dalia Kazzaz, Julia Hillier, Catriona Davies
Keywords:Placental imaging, MR, placental accreta spectrum disorders, antenatal imaging, placenta accreta, placenta praevia
SECTIONS
Educational objective

-Give an overview of the normal placental anatomy

-Describe the phenomenon of placenta praevia and the placenta accreta spectrum (PAS) disorders

-Outline the standard MR protocol and patient preparation to optimise image quality and improve diagnostic certainty

-To demonstrate examples of the various abnormal placental implantations

-Outline helpful tips in approaching placental MR studies

Image 1: T2W axial demonstrates a normal placenta. It is homogenous with a clear placenta-myometrial interface (red arrows).
Image 2: T2W sagittal image showing the placenta attaching low in the uterus but clear of the internal cervical os. Again the clear distinction between the placenta and the myometrium is demonstrated.
Topic Review

Correct and timely diagnosis of an abnormal placental implantation is key to ensuring a safe and planned delivery. A placenta praevia or a placenta accreta spectrum disorder will alter the patient’s care plan as the risk of post partum haemorrhage is increased.

 

A placenta praevia is a placenta covering the internal cervical os whereas PAS disorders occur due to the abnormal invasive implantation of the chorionic villi. The spectrum ranges from the mildest form termed placenta accreta (superficial myometrial invasion) to increta (deep myometrial invasion) with percreta being the most severe form where the placenta extends through the serosa of the uterus.

 

PAS disorders are being recognised more frequently, and MRI is increasingly used as an adjunct to ultrasonography to assess the depth of invasion and lateral...

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Image 3: T2W sagittal showing placenta praevia without placenta accreta.
Image 4: T2W sagittal showing a thinned myometrium anteriorly suggestive of superficial myometrial invasion in keeping with placenta accreta.  The bladder wall returns normal homogenous low T2W signal. The posterior placenta covering the internal cervical os. 
Conclusions

The interpretation of placental MR studies may seem daunting at first however ensuring optimal image quality by adequate patient preparation and having a systematic approach to reporting will increase diagnostic certainty on MR. The increased diagnostic certainty is key to ensuring a smooth patient pathway to a safe delivery for mother and baby.

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