Placenta Accreta Spectrum (PAS): Diagnosis and Management

2D greyscale signs

Loss of the ‘clear zone’

Loss or irregularity of the hypoechoic plane in the myometrium underneath the placental bed (the ‘clear zone’).

Abnormal placental lacunae

Presence of numerous lacunae, including some that are large and irregular (Finberg grade 3), often containing turbulent flow visible in greyscale imaging.

Bladder wall interruption

Loss or interruption of the bright bladder wall (the hyperechoic band or ‘line’ between the uterine serosa and the bladder lumen).

Myometrial thinning

Thinning of the myometrium overlying the placenta to less than 1 mm or undetectable.

Placental bulge

Deviation of the uterine serosa away from the expected plane, caused by an abnormal bulge of placental tissue into a neighboring organ, typically the bladder. The uterine serosa appears intact but the outline shape is distorted.

Focal exophytic mass

Placental tissue seen breaking through the uterine serosa and extending beyond it. Most often seen inside a filled urinary bladder.

2D colour Doppler signs

Uterovesical hypervascularity

Striking amount of colour Doppler signal seen between the myometrium and the posterior wall of the bladder. This sign probably indicates numerous, closely packed, tortuous vessels in that region (demonstrating multidirectional flow and aliasing artifact).

Subplacental hypervascularity

Striking amount of colour Doppler signal seen in the placental bed. This sign probably indicates numerous, closely packed, tortuous vessels in that region (demonstrating multidirectional flow and aliasing artifact).

Bridging vessels

Vessels appearing to extend from the placenta, across the myometrium and beyond the serosa into the bladder or other organs. Often running perpendicular to the myometrium.

Placental lacunae feeder vessels

Vessels with high velocity blood flow leading from the myometrium into the placental lacunae, causing turbulence upon entry.

3D colour Doppler signs

Intraplacental hypervascularity (power Doppler)

Complex, irregular arrangement of numerous placental vessels, exhibiting tortuous courses and varying calibers.