Ultrasound Imaging of Placenta Accreta With MR Correlation

Abstract

Placenta accreta is abnormal placental adherence or invasion of the myometrium or extrauterine structures. It is increasing in incidence because of increasing number of cesarean sections and is one of the main causes of excessive postpartum hemorrhage. Recognition of this entity is crucial because improved outcomes have been shown when the antenatal diagnosis of placenta accreta is made. Ultrasound is the first-line tool; magnetic resonance imaging (MRI) is complementary. Ultrasound and MRI features and MRI protocols will be reviewed.

Morbidly Adherent Placenta: Ultrasound Assessment and Supplemental Role of Magnetic Resonance Imaging

“…22 In isolation this finding is of doubtful significance, and in conjunction with other supporting signs it should be sought in the second or the early third trimester. 3 Lacunar spaces (Fig. 1): These are irregular vascular spaces in the placenta; presence of lacunar spaces has the highest positive predictive value for presence of accreta with an increasing likelihood for placenta accreta with increase in number.…”

“…2 Lacunar spaces are distinct from placental lakes; the latter are normal findings and are more rounded and demonstrate either no flow or a laminar blood flow pattern on Doppler imaging. 3,18 Loss of the retroplacental clear space: The hypoechoic retroplacental space represents the decidua basalis and its absence is considered to be a sign of placenta accreta. There have been reports of its value with reported detection rate of 93%; however, the false positive rate may be unacceptably high and 21%-50% because this finding may be seen in otherwise normal placenta.…”

“…There have been reports of its value with reported detection rate of 93%; however, the false positive rate may be unacceptably high and 21%-50% because this finding may be seen in otherwise normal placenta. 2,3 Others have found this sign to be unreliable with a sensitivity and specificity of only 7% and 6%, respectively. 24 The retroplacental clear space sign is technically difficult because it is angle dependent and is challenging to consistently identify in an anterior placenta.…”

“…When the chorionic villi are attached to the myometrium it is referred to as accreta vera, increta is when the chorionic villi invade the myometrium, and percreta is when it invades through the myometrium and involves the serosa and the adjacent organs such as the bladder, ureters, or the bowel. 2,3 It has been pointed out that the term morbidly adherent placenta more precisely defines the pathologic entity than placenta accreta. Most (75%) of the morbidly adherent placentas represent accretas; a small percentage (7%) of placentas represent percretas that by definition have invaded the myometrium and breached the uterine serosa with extrauterine extension.…”

“…In patients with a prior cesarean delivery and placenta previa there is an 11% incidence of accreta that increases to 41% and 60% in those with 2 or 3 prior cesarean deliveries, respectively. 3 Increasing rates of cesarean deliveries have contributed to steady upward trend in the incidence of placenta accreta. Others have reported that in patients with placenta previa alone there is a 5% risk of placenta accreta; in those with a prior cesarean delivery this increases to 20%, and 40% or higher in those with more than 2 cesarean deliveries.…”