Retained placenta accreta: MRI and pathologic correlation

Use of Postpartum Magnetic Resonance Imaging for Diagnosis and Classification of Retained Placenta Tissue

OBJECTIVE

To study the potential application of magnetic resonance imaging (MRI) for classification of retained placental tissue (RPT) in the uterus postnatally.

METHODS

Twenty-two patients with clinically or pathologically proven RPT were studied.

RESULTS

The thickness ratio (D1/D2) of invaded (D1) to normal (D2) myometrium could be categorized into 3 groups (>0.6, 0.1-0.6, and <0.1) correlating with the 3 types of RPT: accreta vera (RPA), increta (RPI), and percreta (RPP) (r = -0.861, P < 0.01). After uterine arterial embolization, the RPT showed lower signal intensity than the myometrium without flow voids on T2-weighted images. Two cases of RPP showed gradual enhancement, except 1 case of infection and 2 cases that did not involve enhancement examinations, whereas 17 cases of RPA and RPI showed early enhancement.

CONCLUSIONS

Magnetic resonance imaging can facilitate diagnosis of RPT severity. Dynamic contrast enhancement can indicate RPT activity and blood supply, thereby ensuring appropriate clinical decision making.

Placental vascularity and resorption delay after conservative management of invasive placenta: MR imaging evaluation

OBJECTIVES

To assess the potential of magnetic resonance (MR) imaging in evaluating placental vascularity and predicting placental resorption delay after conservative management of invasive placenta.

METHODS

MR examinations of 23 women with conservative management of invasive placenta were reviewed. Twelve women had pelvic embolisation because of postpartum haemorrhage (Group 1) and 11 had no embolisation (Group 2). Comparisons between the two groups were made with respect to the delay for complete placental resorption at follow-up MR imaging and degree of placental vascularity 24 h after delivery on early (30s) and late (180 s) phase of dynamic gadolinium chelate-enhanced MR imaging.

RESULTS

The median delay for complete placental resorption in the cohort study was 21.1 weeks (range, 1-111 weeks). In Group 1, the median delay for complete placental resorption was shorter than in Group 2 (17 vs 32 weeks) (P = 0.036). Decreased placental vascularity on the early phase was observed in Group 1 by comparison with Group 2 (P = 0.003). Significant correlation was found between the degree of vascularity on early phase of dynamic MR imaging and the delay for complete placental resorption (r = 0.693; P < 0.001).

CONCLUSIONS

MR imaging provides useful information after conservative management of invasive placenta and may help predict delay for complete placental resorption.

Postpartum MR diagnosis of retained placenta accreta

Retained placenta accreta can cause catastrophic postpartum hemorrhage. This study aims to determine whether MR imaging can differentiate retained placenta accreta from postpartum hemorrhage caused by other conditions. Fourteen cases suspicious for retained placenta were examined with MR imaging. Signal intensity, the enhancing pattern of uterine contents, and flow voids within the myometrium were retrospectively studied. As hysterectomy was performed in only two cases, final diagnosis was based on clinical outcome and analysis of uterine contents. Final diagnoses were retained placenta accreta in seven cases, retained normally attached placenta in four, hematoma in two, and placental site trophoblastic tumor (PSTT) in one. All seven cases with placenta accreta had a very hyperintense area on T2-weighted images, showing transient early enhancement. None demonstrated delayed strong enhancement around the hyperintense area. In two cases with retained normally attached placenta and in both with hematomas, there were no hyperintense areas on T2-weighted images. Of these, only one showed transient early enhancement. Flow voids were observed in four cases with placenta accreta, one with normally attached placenta, and the case with PSTT. A markedly hyperintense area on T2-weighted images and transient early enhancement without delayed strong enhancement between the mass and the myometrium can indicate retained placenta accreta.

MR imaging of retained products of conception

OBJECTIVE

The objective of this article is to describe the MR imaging appearances of retained products of conception.

CONCLUSION

Retained products of conception appear on MR imaging as an intracavitary uterine soft-tissue mass with variable amounts of enhancing tissue and variable degrees of myometrial thinning and obliteration of the junctional zone. These findings should not be misinterpreted as indicating gestational trophoblastic disease, particularly in the setting of a postpartum patient with a normal or minimally elevated beta-human chorionic gonadotropin level. MR imaging may also be helpful in showing anatomic variants that hinder successful instrumentation of the uterine cavity in patients with suspected retained products of conception.

Fast MR imaging in obstetrics

Ultrasonography (US) is the initial imaging modality of choice for evaluation of patients in obstetrics. However, the results of US are not always sufficient. Magnetic resonance (MR) imaging, which uses no ionizing radiation, may be an ideal method for further evaluation. Although MR imaging is not recommended during the first trimester and use of contrast material is not recommended in pregnant patients, fast MR imaging is useful in various obstetric settings and can provide more specific information with excellent tissue contrast and multiplanar views. In pregnant patients with acute conditions, various diseases (eg, red degeneration of a uterine leiomyoma) may be diagnosed. MR imaging allows characterization of pelvic masses discovered during pregnancy and diagnosis of postpartum complications (eg, abscess, hematoma, ovarian vein thrombosis). In pregnant patients with hydronephrosis, MR urography can demonstrate the site of obstruction and the cause (eg, a ureteral stone). MR pelvimetry may be beneficial in cases of breech presentation. Contrast material-enhanced dynamic MR imaging allows one to evaluate the vascularity of a placental polyp, detect the viable component of a gestational trophoblastic tumor, and diagnose a uterine arteriovenous malformation. MR imaging enables diagnosis of rare forms of ectopic pregnancy and early diagnosis of ectopic pregnancy.

Comprehensive MR imaging of acute gynecologic diseases

Rapid advances in techniques of magnetic resonance (MR) imaging have enabled diagnosis of acute gynecologic conditions, which are characterized by sudden onset of lower abdominal pain, fever, genital bleeding, intraperitoneal bleeding, or symptoms of shock. The chemical-selective fat-suppression technique not only helps establish the characteristics of lesions that contain fat components but also increases the conspicuity of inflammatory lesions. When a T2-weighted image is obtained with a very long effective echo time (>250 msec), even a small amount of ascites can be easily identified and the contrast between urine and complex fluid becomes more conspicuous. T2*-weighted images are useful for identification of hemorrhagic lesions by demonstrating deoxyhemoglobin and hemosiderin. Contrast material-enhanced dynamic subtraction MR imaging performed with a three-dimensional fast field-echo sequence and a rapid bolus injection of gadopentetate dimeglumine allows evaluation of lesion vascularity and the anatomic relationship between pelvic vessels and a lesion and allows identification of the bleeding point by demonstrating extravasation of contrast material. To optimize the MR imaging examination, attention should be given to the parameters of each pulse sequence and proper combination of the sequences.

Placenta accreta: MRI antenatal diagnosis and surgical correlation

We describe a case of a placenta previa accreta that was diagnosed antenatally by MRI with subsequent surgical confirmation. We show the advantages of ultrafast MRI single shot (SS) fast spin echo (FSE) techniques for accurate diagnosis with minimal scan time and fetal motion artifacts.