Diagnostic Ultrasound Findings for Placenta Accreta Spectrum
Key Clinical Context
- The American College of Obstetricians and Gynecologists notes that placenta previa is present in >80% of placenta accreta spectrum cases, particularly in patients with prior cesarean delivery 1, 2, 3, 4, 5, 6
Gray-Scale Ultrasound Findings
- The presence of multiple vascular lacunae within the placenta represents the most specific finding, appearing as irregular sonolucent spaces with the highest positive predictive value for diagnosis 1, 2, 3, 4, 5, 6, 7
- Loss of the normal hypoechoic retroplacental clear zone between placenta and myometrium is a finding, though it has lower specificity and generates more false positives, particularly in the third trimester 1, 2, 3, 4, 5, 6
- Decreased retroplacental myometrial thickness <1 mm indicates deep placental invasion 1, 2, 3, 4, 5, 6, 7
- Abnormalities of the uterine serosa-bladder interface, including interruption or irregularity of the hyperechoic interface between uterine serosa and bladder wall, are associated with placenta accreta spectrum 1, 2, 3, 4, 5, 6
- Extension of placenta into myometrium, serosa, or bladder suggests deeper invasion 1, 2, 3, 4, 5, 6
Color Doppler Findings
- Turbulent lacunar blood flow is the most common and diagnostically useful Doppler finding for placenta accreta spectrum 1, 2, 3, 4, 5, 6, 8, 7
- Increased subplacental vascularity with hypervascularity at the placental bed is a finding 1, 2, 3, 4, 5, 6, 7
- Gaps in myometrial blood flow indicating disruption of normal uterine vasculature are associated with placenta accreta spectrum 1, 2, 3, 4, 5, 6
- Vessels bridging the placenta to the uterine margin or bladder are a finding 1, 2, 3, 4, 5, 6, 7
Diagnostic Approach Algorithm
- The American College of Obstetricians and Gynecologists recommends using combined transvaginal and transabdominal ultrasound with high-frequency (5-9 MHz) linear probe when body habitus permits 7
- Ensure bladder is moderately full (200-300 mL) to properly evaluate the lower uterine segment and cesarean scar area 7
- Apply minimal probe pressure when assessing the retroplacental clear zone to avoid artifactual loss 7
- Add color Doppler and power Doppler imaging to significantly improve detection sensitivity 7, 8