ETIOLOGY OF PLACENTA ACCRETA

The basal plate of the placenta normally limits extension of fetal components into the myometrium, and facilitates placental separation from the myometrium at delivery (1).

A plexus of endometrial decidual veins runs parallel to the uterine wall at the periphery of the basal plate, and drains the placenta.

The sonographic subplacental hypoechoic zone corresponds to these dilated venous channels and marks the peripheral extent of the decidua basalis (2).

Pathologic studies describe an anomalous arterial supply to the placenta (3,4). The physiological changes of placentation, normally limited to the spiral arteries, may progress retrograde in the uterine arterial tree to the larger radial or arcuate vessels.

No specific anomaly of venous placental circulation has been described; an alternative method of venous drainage must exist in the absence of a normal basal plate (5). This may be related to the prominent venous lakes seen in the above series (5).

REFERENCES

1. Boyd JD, Hamilton WJ. The Human Placenta. Cambridge, England, Heffer, 1970.
2. Smith DF, Folet WD. Real time ultrasound and pulsed doppler evaluation of the retroperitoneal clear area. J Clin Ultrasound 1982;10:215.
3. Khong TY, Robertson WB. Placenta creta and placenta previa creta. Placenta 1987;8:399.
4. Minh HN, Smadja A, Orel L. The morphogenesis of uteroplacental circulation in placenta accreta. Arch Anat Cytol Pathol 1983;31:101.
5. Hoffman-Tretin JC, Koenigsberg M, Rabin A, Anyaegbunam A. Placenta Accreta. Additional sonographic observations. J Ultrasound Med 1992;11:29-34.