Placenta accreta spectrum (PAS): standardized ultrasound findings and assessment protocol

Standardized ultrasound criteria for PAS

According to criteria proposed by Alfirevic et al. and Collins et al. (ISUOG, Ultrasound Obstet Gynecol, 2024), the following sonographic findings are used for diagnosis of placenta accreta spectrum:

• abnormal placental lacunae;
• myometrial thinning;
• loss of the clear zone;
• bladder wall interruption;
• placental bulge;
• focal exophytic mass;
• uterovesical hypervascularity;
• subplacental hypervascularity;
• bridging vessels;
• placental lacunae feeder vessels.

Standardized descriptors for reporting

Placental parenchymal changes are recommended to be described using standardized descriptors (ISUOG, Ultrasound Obstet Gynecol, 2024): size, number, location, and relationship to abnormalities of the uterine contour — lack of clear space, myometrial thinning, and placental bulging — and abnormalities of uteroplacental circulation.

Protocol for sequential assessment

In the cited study, suspicious cases were evaluated at three sequential stages: preoperative, intraoperative, and postoperative (ISUOG, Ultrasound Obstet Gynecol, 2024). This stepwise approach ensures correlation of sonographic findings with surgical and pathological data.

Scoring scales

Scoring systems are used to standardize assessment. For recording placental lacunae, the scale proposed by Finberg and Williams was used (ISUOG, Ultrasound Obstet Gynecol, 2024). Ultrasound scoring scales with correlation to surgical and neonatal outcomes have also been developed (Del Negro V. et al., Diagnostics, 2020), as well as criteria for differentiation of placenta accreta from percreta (Cali G. et al., Ultrasound Obstet Gynecol, 2013).

Specific numerical thresholds and scoring values of the aforementioned scales are not provided in the source fragments [to be verified].