Placenta percreta is a term given to the most severe but least common form of the placenta accreta spectrum disorders, where there is a transmural extension of placental tissue across the myometrium with a serosal breach. It carries severe maternal as well as fetal risks.

The milder end of the spectrum of abnormal placental villi adherence are:

• placenta accreta

• placenta increta

Epidemiology

It represents ~5% of all types of abnormal villous adherence. The incidence is thought to be increasing, probably due to the increasing practice of caesarean sections (which is a risk factor).

Risk factors 

• prior caesarean section

• placenta praevia

• advanced maternal age

• uterine anomalies

• intrauterine adhesion bands

• previous surgery

Pathology

It is characterised by transmural extension of placental tissue across the myometrium with a serosal breach. Placental invasion of the myometrium is related to a thinned decidual endometrium at the site of implantation and this can happen for a number of reasons.

Radiographic features

US

Ultrasound may identify:

• protrusion of placental tissue beyond the outer confines of the uterine myometrium

• increased vascularity between serosa and adjacent structures such as the bladder

MRI

MRI features of placenta percreta ⁸:

• uterine bulging

• lumpy placental contour

• rounded placental edges

• intraplacental hypointense bands, are more evident in placenta percreta when compared with placenta accreta or placenta increta

• full-thickness gap of myometrial signal with loss of fat plane between the placental tissue and adjacent pelvic organs and intermediate placental signal disrupting the hypointense line of the bladder, bowel wall, or abdominopelvic wall muscles

Treatment and prognosis

Surgical intervention is a mainstay of treatment in most cases. However, bleeding during the intervention is a serious concern especially in a situation where adjacent organs such as bladder or bowel are involved. In these circumstances, conservative management is preferred. Embolisation techniques have also been used in selected cases.

Complications

• uterine rupture

• catastrophic peripartum haemorrhage