chorioamniotic separation

Radiopaedia • CC-by-nc-sa 3.0 • de

Chorioamniotic separation (CAS) is an intra-uterine event which can occur in pregnancy and is characterized by separation of placental (chorion) and fetal (amnion) membranes.

Pathology

The membranes are separated in early gestation, accounting for the appearance of the amniotic sac. After approximately 14 weeks gestation, these membranes fuse and are indistinguishable as separate entities. Rarely, a chorioamniotic separation can occur later in gestation. It can be focal or extensive, with the amniotic membrane becoming either free-floating or adherent to the fetus.

Etiology

Most reported cases occur after invasive intra-uterine procedures such as:

previous amniocentesis: small degrees of CAS are frequently present after amniocentesis
hysterotomy

Some cases occur spontaneously which is then termed a primary chorioamniotic separation.

Associations

increased rates of underlying fetal chromosomal and developmental abnormalities have been associated with sporadic cases

Radiographic features

Antenatal ultrasound

A chorioamniotic separation is usually sonographically detected as a visible free-floating or adherent membrane surrounding the fetus. The separation can extend throughout the entire uterine cavity up to the base of the umbilical cord and over the surface of the placenta.

Significance

Sonographic detection of a small chorioamniotic membrane separation especially before 14 weeks gestation is considered a benign incidental finding

Knowledge of potential complications is however useful. A careful search for aneuploidy and other developmental anomalies is often recommended if a spontaneous chorioamniotic separation is detected after 14 weeks.

Complications

Recognized complications following a large separation include :

miscarriage
in utero fetal death
umbilical cord complications
pre-term delivery
amniotic band formation

Differential diagnosis

Considerations for ultrasound appearances include:

amniotic band going through the periphery: can be also a complication of CAS
subchorionic hemorrhage dissecting around the endometrial cavity