Also called circumvallata (= surrounded by a wall).  These are placenta that are a form of placenta extrachorialis, unusual in humans but common in chimpanzee and orang-utan. They are usually benign condition requiring no alteration of management and simply have to be differentiated from other type of bands and membranes in the uterine cavity.

Sonographic criteria of identification include irregular edge, uplifted margin, or placental sheet or shelf resulting from the infolding of the fetal membrane upon the fetal surface of the placenta during the middle of the second trimester. The last criteria being the easiest to identify, is illustrated in several images below.

Case #1

Case #2

Case #3