To describe the features of ultrasound (US) and magnetic resonance imaging (MRI) of pernicious placenta previa (PPP).

Twenty-seven patients (gestational weeks, 20-24) with probable placenta implantation diagnosed by prenatal US or MRI in Affiliated Drum Tower Hospital of Nanjing University from January 2014 to January 2015 were included in this study. Ultrasound follow-up were given to these patients until birth-giving. Their continual US/MRI results and pathological examination results were acquired for comparison.

Ultrasound exams were performed in twenty-seven patients, among which seventeen patients recieved both US and MRI examination. The common sonographic findings of PPP included placenta thickening (14 cases), partial echo loss in myometrium and loss of the normal hypoechoic retroplacental zone (17 cases), placenta pit and rich blood sinus (15 cases) and abundant blood flow in or behind the placenta and blood disorder (21 cases). The frequent sonographic presences of patients with placenta implantation included continuous uterine serosa layer, partial echo loss of muscle layer, obscure placenta base-myometrium interface and loss of the normal hypoechoic retroplacental zone (24 cases). Features of 3 patients with placenta through were discontinuity of uterine serosa layer, partial echo loss of muscle layer, discontinuity of the echo of bladder wall muscle layer, obscure bladder-myometrium interface, low resistance-high speed arterial blood flow and placenta penetration. The common MRI findings of PPP (a total of 17 cases) include continuous signal in uterine junction, myometrium thinning and placenta accreta (2 cases); uterine junction, myometrium thinning or invaded or irregular signal, blood vessels expand circuity, empty vessels through muscularis and placenta increta (10 cases); placental villi penetrates the myometrium of size film layer, completely disappearing myometrium and locating outside the uterus contour line and placenta penetration (5 cases), among which three cases featured interruption of the bladder wall and placental invasion into the bladder. Delivery results: among all patients delivered by caesarean section, seventeen patients underwent temporary occlusion balloon catheter of the internal iliac artery and cesarean section with hysterectomy. Nine patients underwent temporary occlusion balloon catheter of the internal iliac artery and cesarean section without hysterectomy. One patient underwent transcatheter uterine artery embolization and dilatation and curettage. No severe obstetric complications were found in all the 27 cases. The results were consistent among US, MRI and pathology in most of the patients (13/17). Two patients with adherent placenta (confirmed by pathology and MRI) were diagnosed as placenta implantation by US. And two patients with placenta implantation (confiremed by pathology and US) were diagnosed as placenta through by MRI. Ten patients received US examination only. The results were consistent with pathology in most cases (7/10). Three patients who were diagnosed as placenta implantation were confirmed as adherent placenta by pathology.

Ultrasound and magnetic resonance imaging of pernicious placenta previa (PPP) exhibit significant features, which can provide important reference for clinical treatments.

Ultrasonography, Doppler; Magnetic resonance imaging; Placenta previa; Placenta accreta