Too deeply attached placenta

Clinical History

A 34-year-old asymptomatic 36-weeks pregnant woman, G1P0, with placenta previa and an ill-defined uterus–bladder interface on third trimester ultrasound was admitted to our department to perform a magnetic resonance imaging (MRI).
Her medical history revealed a previous hysteroscopic correction of an incomplete septate uterus and no other significant finding.

Imaging Findings

MRI revealed a complete placenta previa.
On T2-weighted images (WI), the placenta is slightly heterogeneous with an inferior hypointense retractile band, just anterior to the internal os, that obliterates the normal myometrium reaching the serosa (Fig. 1a, b). The cleavage plane between the uterus and the bladder seems to be preserved, however, slightly ill-defined (Fig. 1c), denoting placenta percreta/increta features.
A fluid collection with a bright signal is seen, on both T1 and T2-WI (Fig. 2a and 2b respectively), inferior to the placenta and just superior to the internal os, demonstrating a retroplacental acute haemorrhage.

Discussion

Placenta accreta (PA) occurs when placental implantation is abnormal due to a defect in the decidua basalis that allows the anchoring fetal chorionic villi to abnormally adhere, penetrate into/through the myometrium. When there is only superficial invasion of the decidual layer the condition is designated as PA vera (around 75% of cases), if there is deeper myometrial invasion or involvement of the uterine serosa/adjacent pelvic organs the terms placenta increta or percreta are used, respectively [1, 2]
. However, frequently the designation placenta accreta is used for ease of description as a general term for all of these conditions.
The exact pathogenesis is unknown, but possible causes include prior uterine wall trauma (mainly related to caesarean section or curettage) and eventually an abnormal maternal response to trophoblastic invasion [2]. The estimated prevalence is increasing (around 1 in 1000-2500 deliveries) but varies widely due to the use of different diagnostic criteria [1, 2].
PA is a potentially life-threatening obstetric condition that can result in severe haemorrhage at the time of placental delivery, so antepartum diagnosis is essential to minimize potential maternal or neonatal morbidity and mortality [1].
Ultrasound is the first choice to evaluate the placenta. Typical features of PA are: loss/irregularity of the retroplacental sonolucent zone (disruption of the normal hypoechoic myometrium under placental tissue), abnormal placental lacunae with turbulent flow (peak systolic velocity over 15 cm/s), markedly dilated vessels over peripheral sub-placental zone, anomalies of the bladder-myometrium interface [3, 4].
MRI represents a significant improvement in diagnostic accuracy in cases where the sonographic diagnosis is not straightforward, allowing a better evaluation of the myometrial invasion, however, the serosa penetration is frequently difficult to define [5]. MRI features include abnormal uterine bulging, heterogeneous placental signal intensity on T2-WI and the presence of T2-dark intraplacental bands [3, 4]. Some authors recommended contrast-enhanced studies in order to improve specificity and to better define the depth of myometrial invasion, allowing a better distinction between PA vera, percreta and increta, however, the use of gadolinium is not consensual in pregnancy [6].
In general, the therapeutic approach includes a planned preterm caesarean hysterectomy, however various treatment strategies have been employed, including leaving the placenta in situ (because attempts at removal of the placenta are associated with significant haemorrhagic morbidity), with or without endovascular embolization and/or methotrexate therapy [4, 7].
Even though antenatal imaging techniques are of great help in identifying a morbidly adherent placenta, the exact diagnosis is still difficult to establish.

Differential Diagnosis List

Final Diagnosis

Placenta previa percreta/increta

URL:	https://www.eurorad.org/case/11882
DOI:	10.1594/EURORAD/CASE.11882
ISSN:	1563-4086