Amniotic sheets: Imaging features, subtypes, and obstetric outcomes

Amniotic sheets, or amniotic shelves, are intrauterine membranes that develop when the amnion and chorion reflect against preexisting uterine synechiae. While amniotic sheets are not associated with fetal malformations, growing evidence suggests that certain amniotic sheet features may be linked with obstetric and fetal risks, such as fetal malpresentation. In this pictorial review, we evaluated the ultrasound (US) and magnetic resonance (MR) imaging features of various amniotic sheet subtypes and their obstetric outcomes.

This pictorial essay identified the distinct US and MR imaging features, as well as relevant obstetric and fetal outcomes, in four different cases of amniotic sheets. We summarized the distinguishing characteristics of amniotic sheets as compared to other intrauterine echogenicities, and we showed that amniotic sheet subtypes can significantly differ in location, orientation, degree of uterine compartmentalization, and presence of discontinuities. In rare cases, obstetric and fetal complications occurred in the setting of sheet subtypes with marked compartmentalization and discontinuities.

The thorough characterization of amniotic sheets on prenatal imaging can help guide appropriate patient counseling, surveillance imaging, and delivery planning. Certain features, such as the degree of uterine compartmentalization and presence of discontinuities, may be particularly important when evaluating amniotic sheets. While US remains the first-line modality for detecting amniotic sheets, three-dimensional (3D) US serves an important role in further characterizing sheet subtypes based on uterine location, compartmentalization, and discontinuities. MR imaging can further clarify the extent of amniotic sheets and the degree of uterine compartmentalization.