Abnormal Placental Lacunae
From: Collins SL, Ashcroft A, Braun T, Calda P, Langhoff-Roos J, Morel O, et al. Proposal for standardized ultrasound descriptors of abnormally invasive placenta (AIP). Ultrasound Obstet Gynecol. 2016;47(3):271-5.
Pathophysiology of lacunae development.
In severe PAS, placental tissue is found more deeply within the myometrium than in normal placentation, often reaching the radial and arcuate vessels. The resulting dilatation of these high pressure arteries and a greatly increased velocity of flow into the intervillous space distorts the architecture of the placental cotyledon and its corresponding inter-lobar septa. This powerful flow results in lacunae formation.
Although these lacunae can sometimes be seen throughout the whole placenta, given the mechanism of their formation they should be seen to be adjacent to the basal plate of the placenta. If the ‘placental holes’ seen are only on the fetal side of the placenta or just at the edges, it must be carefully considered as to whether they actually are PAS-related lacunae.
From A simple guide to ultrasound screening for placenta accreta spectrum for improving detection and optimizing management in resource limited settings. Adu-Bredu T. K. , Rijken M. J., Nieto-Calvache A.J., Stefanovic V., Aditya Aryananda R., Fox K.A. , Collins S. L. Int J Gynecol Obstet. 2022;00:1–10.
Lakes and echogenic cystic lesions
PAS-related lacunae must not be confused with placental lakes or echogenic cystic lesions. Placental lakes are cystic spaces (>10mm) often located centrally within the cotyledon or lobule surrounded by normal echogenicity placental parenchyma. Lakes are frequently confused with PAS-related lacunae and the terms ‘lake’ and ‘lacunae’ are often used interchangeably. This is evidenced by studies which report the presence of lacunae in normal placentation in low-risk pregnancies. On grey-scale imaging, lacunae and lakes appear as hypoechoic areas within the placenta. However, PAS-related lacunae are often irregularly ellipsoid in shape and extend from the placental bed where they receive blood supply from the feeder vessels (radial or arcuate arteries). Placental lakes may be easily compressible with the ultrasound probe and often contain slow moving blood while typical PAS lacunae are incompressible. It must be noted that, lacunae and lakes can be present in the same PAS placenta. They should be differentiated by their size and location. PAS-related lacunae are also numerous in the region of the abnormal placentation while lakes are usually few in number and widely distributed.
Placental infarcts result from interrupted maternal blood supply to the placenta and often present as hypoechoic region with hyperechogenic rim (echogenic cystic lesion) or well – circumscribed lesion with mixed echogenicity and are often associated with pre–eclampsia and fetal growth restriction. Placental infarcts can be differentiated from lakes and lacunae by the characteristic hyperechoic rim.
From A simple guide to ultrasound screening for placenta accreta spectrum for improving detection and optimizing management in resource limited settings. Adu-Bredu T. K. , Rijken M. J., Nieto-Calvache A.J., Stefanovic V., Aditya Aryananda R., Fox K.A. , Collins S. L. Int J Gynecol Obstet. 2022;00:1–10.