MRI evaluation of invasive placenta: “Cool” answers to radiologists’ “hot” questions, p. 39-48
VOLUME 2 | ISSUE 1
HJR
Women’s Imaging Review
MRI evaluation of invasive placenta:
“Cool” answers to radiologists’
“hot” questions
Charis Bourgioti, Konstantina Zafeiropoulou, Lia Angela Moulopoulos
Department of Radiology, National and Kapodistrian University of Athens, School of Medicine, Areteion Hospital, Greece
Submission: 29/06/2016 | Acceptance: 30/11/2016
Abstract
During the last decades, the incidence of invasive ery planning. Suspicious MRI findings for abnormal
placenta has risen significantly, probably due to placentation include, marked placental heteroge-
the increased rate of caesarian delivery. Invasive neity, low T2 signal intraplacental bands, exten-
placenta may cause massive intra-or postpartum sive intraplacental vascularity, focal uterine bulge,
hemorrhage; therefore, prenatal diagnosis of the myometrial thinning or disruption with loss of ute-
presence and extent of myometrial invasion or ex- ro-placental interface, bladder ‘tenting’ and the pla-
trauterine placental spread is critical for optimal cental protrusion sign. Currently, there is no official
management. Sonography is the imaging modality standardization of MRI protocols and there are no
of choice for the evaluation of abnormal placenta; large series addressing the interobserver variabil-
MRI performs equally well and can be used as a re- ity for the evaluation of invasive placenta. The aim
liable alternative in cases of equivocal sonographic of this review is to report current literature data
findings. Indications for MRI include evaluation of regarding MRI assessment of invasive placenta in
a posteriorly located placenta and the need for pre- an attempt to familiarize radiologists with the ‘hot’
cise delineation of placenta percreta for pre-deliv- topic of abnormal placentation.
placenta accreta; placenta percreta; placenta increta; ultrasound (US);
Key words Magnetic Resonance Imaging (MRI)
Charis Bourgioti, MD. Department of Radiology, National and Kapodistrian
Corresponding University of Athens, School of Medicine, Areteion Hospital, 76 Vassilisis Sofias
Author, Ave., 11528, Athens, Greece
Guarantor E-mail: charisbourgioti@yahoo.com
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, HJR MRI evaluation of invasive placenta: “Cool” answers to radiologists’ “hot” questions, p. 39-48
VOLUME 2 | ISSUE 1
1. Introduction the lower uterine segment, within 2 cm from the internal
The term “placenta” originates from the Greek word cervical os; two main types of placenta previa are defined:
plakuos, which means “flat cake”. Indeed, placenta is the Complete previa, when placenta completely covers the in-
“cake” for the fetus, as it is responsible for its nutrition ternal os and marginal previa, when the leading edge of
and its respiratory and excretory function. Prenatal eval- the placenta is less than 2 cm from the internal os and ad-
uation of the abnormal placenta is a “hot” topic for both vanced maternal age (>35 years). Minor risk factors associ-
gynecologists and radiologists; early identification of in- ated with invasive placenta include Asherman’s syndrome
vasive placenta and accurate preoperative diagnosis re- (i.e. the presence of adhesions within uterine cavity), uter-
garding the degree of myometrial invasion and extrauter- ine fibroids [1] and history of uterine surgeries, including
ine spread, are critical for optimal management. curettage, abortions or myomectomy [2].
Magnetic Resonance Imaging (MRI) may provide im- Invasive placenta may spontaneously develop in a small
portant information for pre-delivery planning in patients percentage (0.4%) of the general population. Its incidence
with invasive placenta; however, accurate interpretation increases significantly (5%) when placenta previa is pres-
of the MRI appearance of invasive placenta requires ex- ent. If the patient also has a history of a single C-section,
pertise. The aim of this study is to review current litera- the incidence rises to 24%; when placenta previa is asso-
ture data regarding MRI diagnostic performance for the ciated with multiple prior (>3) C-sections, the risk for ab-
evaluation of invasive placenta and to familiarize radiolo- normal placentation becomes extremely high (67%) [3].
gists with common MRI features of abnormal placentation. Invasive placenta may be a life-threatening condition
We have conducted a literature search using MEDLINE during delivery, because of the increased risk of massive
(PubMed) Library. Applied key words included: Invasive intra- or postpartum haemorrhage, as the abnormal pla-
placenta; placenta accreta; placenta increta; placenta per- centa is strongly attached to the myometrium and cannot
creta; MRI; US. The search period extended from July 1985 be completely separated from the uterus, potentially caus-
to March 2016. Prospective or retrospective original re- ing uncontrollable bleeding. Massive blood loss (>3-5 l)
search studies and review articles with or without me- may cause disseminated intravascular coagulopathy (DIC),
ta-analysis data were reviewed; selection of the studies renal failure, adult respiratory distress syndrome (ARDS)
was performed by consensus from all authors and it was and death. Reported maternal mortality rates due to inva-
based on the presence of the following criteria: Appro- sive placenta reach 7% [4-7]. Therefore, accurate prenatal
priate study design, adequate study population (>20 pa- diagnosis becomes an important issue for clinicians, in or-
tients), use of clear diagnostic evidence, reliable statistical der to appropriately schedule delivery and minimize ma-
data and reproducibility of the results. A total of 33 stud- ternal and neonatal risks. Patients with invasive placenta
ies were finally included in our review report. are usually scheduled for C-section at 34-35 weeks, in an
attempt to limit the risk of fetal lung immaturity.
2. Clinical information The management of placental invasion requires a multi-
Invasive placenta is a serious pregnancy condition, char- disciplinary approach with participation of a well-trained
acterized by a defect of the desidua, through which the fe- surgical team (e.g. gynecologists, urologists), dedicat-
tal trophoblast (chorionic villi) extends to the myometri- ed anesthesiologists and pediatricians. Blood products
um. There are three types of invasive placenta, based on should be readily available. Interventional radiology tech-
extent of myometrial invasion: (a) placenta accreta (the niques, such as perioperative internal iliac artery occlu-
least invasive type), where the villi attach to the myome- sion, may be employed, in order to reduce blood loss dur-
trium and may superficially invade it, (b) placenta incre- ing surgery and subsequent need for transfusion [8, 9].
ta, where the villi partially invade the myometrium and
(c) placenta percreta, where the villi completely penetrate 3. Discussion
the myometrium, reaching to the uterine serosa, with or
without invasion of the surrounding extrauterine tissues. 3.1 Sonography: Is it enough for the diagnosis
Well-established risk factors associated with invasive of invasive placenta?
placenta include a previous Cesarean section (C-section), Transabdominal gray scale and Color Doppler sonogra-
presence of placenta previa (i.e. location of the placenta at phy is the first-line imaging modality used to evaluate
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