Subchorionic placental cysts are quite rare, and their etiology remains controversial. In some cases, they are associated with fetal growth restriction and intrauterine asphyxia. In this work, we describe a case of a large subchorionic cyst arising near the placental cord insertion site, complicated by an intracystic hemorrhage and diagnosed by ultrasound.
An 18-year-old gravida 1 para 1 woman presented at our institution at 23 weeks of gestation for a routinely obstetrical ultra- sound examination. This patient had no past medical history, except a small constitution.
Ultrasonographic examination performed revealed a harmonious fetal growth restriction with a biometry corresponding to -2SD. However, limbs and amniotic fluid index were normal for the term. A large cystic structure measuring 85 mm was found near the placental cord insertion site (figures 1 and 2).
The intracystic contain was heterogeneous and hyperechoic, due to intracystic hemorrhage. Blood flow was not detected in the cystic structure on color Doppler ultrasound. A Doppler examination of the umbilical, the cerebral and the uterine arteries revealed normal velocity and pulsatility.
Figure 1 : Ultra-sound examination at 23 weeks of gestation demonstrating a heterogeneous and hyperechoic cyst in the fetal surface of the placenta (asterisk).
Figure 2 : Hemorrhagic placental cyst (asterisk) near the placental cord (arrow).
DEFINITION Cystic masses arising from the fetal surface of the placenta have been referred to by different terms, including “subchorionic cysts,” “chorionic cysts,” “subamniotic cysts” and “membranous cysts”. Their etiology remains controversial. The majority of them are usually smaller than 2 cm in diameter and tend to occur in women with diabetes mellitus or maternal rhesus incompatibility. Our patient had none of these conditions.
ANATOMOPATHOLOGY Microscopically, the walls in these cysts appear to consist of amniotic and chorionic membranes. It has been suggested that X cells (trophoblastic cells having a secretory activity) may be associated with the formation of these cysts. X cells can be found near areas of fibrinoid degeneration and within the lining of the cystic wall.
IMAGING Sonographic examination indicates that non complicated subchorionic cysts occur as echo-free cavities under the fetal plate. There is no blood flow within these lesions. Therefore, they do not induce a Doppler signal. These features were found in our case. Intracystic hemorrhage leads to an increasing size and a heterogeneous and hyperechoic contain of the cyst.
CLINICAL OUTCOME (1) There are contradictory opinions concerning the clinical importance of subchorionic cysts. Most of them have been reported to be of no clinical importance. Conversely, some authors reported an association with intrauterine growth restriction.
CLINICAL OUTCOME (2) Fetal growth restriction appears to be more frequent in case of large and multiples cysts. The relationship between placental cyst and placenta vessel is variable. Frequently, fetal chorionic vessels are elevated by these distended cysts, but this usually does not interfere with fetal circulation.
CLINICAL OUTCOME (3) However, low birth weight and abnormal Doppler measurements have been reported for patients with a subchorionic cyst. Some authors explained that the placental cyst located near the placental cord insertion site causes fetal growth restriction, because it constricts and interferes with umbilical cord circulation.
MAIN DIFFERENTIAL DIAGNOSES : Subamniotic hematomas : They occur after a fetal vessel rupture and are usually found beneath the amniotic layer covering the fetal plate of the placenta. On ultrasonography, they appear as a single mass covered by a thin membrane and protruding from the fetal plate.
They are located mainly within the placental tissue and are characterized by a turbulent blood flow on real-time ultrasonography. Placenta avillous spaces or “placental lakes” : Subchorionic hematomas: They result from bleeding that is maternal in origin. On ultrasonography, they appear as a hypoechoic area between the chorion and the uterine wall.
Most subchorionic cysts are thought to be obstetrically harmless. However, a large subchorionic cyst near the placental cord insertion site should be considered a pathological lesion and followed closely by US examination, to rule out a secondary intracystic hemorrhage, a partial occlusion of umbilical cord blood flow, a fetal growth restriction secondary to the cyst or an intraamniotic rupture leading to fetal death.