Detection of suspected placental invasion by MRI: Do the results depend on observer’ experience?

doi:10.1016/j.ejrad.2012.08.022

European Journal of Radiology

Volume 82, Issue 2, February 2013, Pages e51-e57

https://doi.org/10.1016/j.ejrad.2012.08.022 Get rights and content

Abstract

Purpose

To evaluate the diagnostic value of previously described MR features used for detecting suspected placental invasion according to observers’ experience.

Materials and methods

Our population included 25 pregnant women (mean age 35.16) investigated by prenatal MRI (1.5 T, T1- and T2-weighted MR-sequences without i.v. contrast), among them 12 with histopathologically proven placental invasion and 13 women (52%) without placental invasion used as control group. Two senior and two junior radiologists blindly and independently reviewed MR-examinations in view of 6 previously defined MR-features indicating presence and degree of placental invasion (placenta increta, accreta or percreta). For each reader the sensibility, specificity, and receiver operating curve (ROC) were calculated. Interobserver agreements between senior and junior readers were determined. Stepwise logistic regression was performed including the 6 MR-features predictive of placental invasion.

Results

Demographics between both groups were statistically equivalent. Overall sensitivity and specificity for placental invasion was 90.9% and 75.0% for seniors and 81.8% and 61.8% for juniors, respectively. The best single MR-feature indicating placental invasion was T2-hypointense placental bands (r² = 0.28), followed by focally interrupted myometrial border, infiltration of pelvic organs and tenting of the bladder (r² = 0.36). Interobserver agreement for detecting placental invasion was 0.64 for seniors and 0.41 for juniors, thus substantial and moderate, respectively. Seniors detected placental invasion and depth of infiltration with significantly higher diagnostic certitude than juniors (p = 0.0002 and p = 0.0282, respectively).

Conclusion

MRI can be a reliable and reproducible tool for the detection of suspected placental invasion, but the diagnostic value significantly depends on observers’ experience.

Introduction

Disorders of placental implantation are currently classified as abnormal localization and abnormal attachment. Abnormalities in placental localization are far more commonly encountered (1/250 pregnancies) than abnormalities in placental attachment (1/5000 pregnancies). Attachment abnormalities include three entities: placenta accreta, increta and percreta, which represent a spectrum of placental adhesive disorders, with increasing severity (Fig. 1). These placental implantation disorders are a significant cause of maternal morbidity and mortality. Their prevalence is currently on the rise because of the growing percentage of older pregnant women and those with previous abortions and/or caesarean sections [1], [2].

The diagnosis and management of women at risk is not only based on clinical parameters, but also driven by imaging, namely ultrasound (US) and, more recently, magnetic resonance imaging (MRI). Prenatal US is formerly considered as the routine diagnostic standard examination, but fetal MRI is emerging as an alternative and complementary method, used in case of ultrasonographic suspicion of placenta attachment anomalies, but equivocal diagnosis. In the past decade, several MR imaging features have been described and considered useful for predicting abnormal placental implantation [1], [2], [3], [4], [5], [6], [7], [8]. However, these MR signs may be subtle and difficult to detect, in particular when the radiologist has limited experience.

The purpose of this study was to exactly assess the diagnostic value of specific MR features for detecting suspected placental invasion according to the radiologists’ working experience.

Section snippets

Patients

Our study population included 25 pregnant women (mean age 35.16) who had been consecutively investigated by prenatal MRI between June 2007 and December 2009 after obstetrician referral for suspected placental invasion upon standard pregnancy US examinations. The patients were followed and treated in one of the three different University Hospitals that took part in this retrospective study. Nineteen patients presented placenta previa and three out of them had an additional history of previous

Patients population

Demographics between the two groups were similar. Neither the mean age of the patients (p = 0.692) nor the gestational age at MR examination (p = 0.672) differed significantly. For the group with placental invasion, the mean age of the women was 35.5 years and the mean gestational age 31.1 weeks, whereas for the control group they were 34.8 years and 31.9 weeks, retrospectively.

Nineteen (76%) out of the 25 women had placenta previa, including 11 of 12 patients with proven placental invasion.

Discussion

Abnormalities in placental attachment include three entities: placenta accreta, increta and precreta. These are a spectrum of placental adhesive disorders, with increasing grade of placental invasion into the myometrium (Fig. 1). Placenta accreta is the most frequent and less severe form, caused by the penetration of the deciduas by the chorionic villi. Placenta increta consists in a partial invasion of the myometrium by the villi, and placenta percreta, the most severe form, implies the

Conclusions

In conclusion, the medical practice faces an increased prevalence of placental adhesive disorders in the near future because of a higher mean maternal age and an increase of uterine surgery procedures. Today, MRI of the placenta has become a complementary method to US for patients at risk and in selected, equivocal cases. Different MR features have been described in association with placental disorders, but our results suggest that their recognition and correct interpretation very much depend

Acknowledgment

We would like to thank Ms. Kevin Decitre for the drawing of Fig. 1.

References (15)

A. Lax et al.
The value of specific MRI features in the evaluation of unsupected placental invasion
Magnetic Resonance Imaging
(2007)
C. Maldjian et al.
MRI appearance of placenta percreta and placenta accreta
Magnetic Resonance Imaging
(1999)
T.H. Teo et al.
Use of magnetic resonance imaging in evaluation of placental invasion
Clinical Radiology
(2009)
T.Y. Khong et al.
Placenta creta and placenta previa creta
Placenta
(1987)
S. Wu et al.
Abnormal placentation: twenty-year analysis
American Journal of Obstetrics and Gynecology
(2005)
C. Mazouni et al.
Placenta accrete: a review of current advances in prenatal diagnosis
Placenta
(2007)
W.C. Baughman et al.
Placenta accreta: spectrum of US and MR imaging findings
Radiographics
(2008)

There are more references available in the full text version of this article.

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Placental thickness was positively correlated with the estimated blood loss during delivery, while cervical length had a negative correlation with it, based on the adjustment for gestational age. Multivariate analyses revealed that prior cesarean section, placenta previa, increased placental thickness(≧4.35 cm) and short cervical length（< 3.05 cm） were independent risk factors for PPH. When the 4 risk factors were combined together, the AUC was the highest, 0.773 (95%CI 0.707–0.840).
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Overall, the reporting of placenta percreta in the literature is based on the gross findings of hysterectomy specimens presenting with villous tissue having penetrated through the entire uterine wall,5–12 and textbook descriptions are illustrated by diagrams showing placental villi protruding into the peritoneal cavity after crossing the myometrium and uterine serosa.7 These diagrams have been used until today by many authors of diagnostic14,15 and management16 studies to describe the different grades of PAS. Luke et al5 reported that most hysterectomy specimens arrive at the laboratory distorted by attempts to remove the placenta during delivery, limiting considerably the macroscopic examination and sampling and adding to the confusion in reporting different grades of PAS in both epidemiologic and clinical studies.
Placenta percreta is described as the most severe grade of placenta accreta spectrum and accounts for a quarter of all cases of placenta accreta spectrum reported in the literature.
We investigated the hypothesis that placenta percreta, which has been described clinically as placental tissue invading through the full thickness of the uterus, is a heterogeneous category with most cases owing to primary or secondary uterine abnormality rather than an abnormally invasive form of placentation.
We have evaluated the agreement between the intraoperative findings using the International Federation of Gynecology and Obstetrics classification with the postoperative histopathology diagnosis in a prospective cohort of 101 consecutive singleton pregnancies presenting with a low-lying placenta or placenta previa, a history of at least 1 prior cesarean delivery and ultrasound signs suggestive of placenta accreta spectrum. Furthermore, a systematic literature review of case reports of placenta percreta, which included histopathologic findings and gross images, was performed.
Samples for histologic examination were available in 80 of 101 cases of the cohort, which were managed by hysterectomy or partial myometrial resection. Microscopic examination showed evidence of placenta accreta spectrum in 65 cases (creta, 9; increta, 56). Of 101 cases included in the cohort, 44 (43.5%) and 54 (53.5%) were graded as percreta by observer A and observer B, respectively. There was a moderate agreement between observers. Of note, 11 of 36 cases that showed no evidence of abnormal placental attachment at delivery and/or microscopic examination were classified as percreta by both observers. The systematic literature review identified 41 case reports of placenta percreta with microscopic images and presenting symptomatology, suggesting that most cases were the consequence of a uterine rupture. The microscopic descriptions were heterogeneous, and all descriptions demonstrated histology of placenta creta rather than percreta.
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The accuracy for seniors with expertise was non-statistically higher (0.83) compared to senior with no expertise (SWE) (0.65) and juniors (0.74) with SWE having tendency to over-estimate the severity of abnormality (26% vs 17%), whilst junior underestimated the degree of placental infiltration when compared to seniors with expertise (18.5% vs 0%, p = 0.006).
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