Circumvallate placenta is a placental morphology anomaly where the chorionic plate is smaller than the basal plate and the membranes (amnion + chorion) fold inward on the fetal surface creating a thickened ring. Incidence is 1-7%, usually recognized in the second trimester. Thickened, folded membranes and fibrin deposits are seen at the chorionic plate edge — the 'rolled edge' appearance is pathognomonic. Subchorionic fibrin and organized hematoma accumulation may be seen along the placental margin. Clinical significance is debated; however, complete circumvallation may increase risk of subchorionic hematoma, abruption, preterm delivery, IUGR, and recurrent bleeding. Partial circumvallation is usually clinically insignificant.
Age Range
18-45
Peak Age
30
Gender
Female predominant
Prevalence
Uncommon
The pathogenesis of circumvallate placenta is not fully understood; decidual hemorrhage in early pregnancy and peripheral limitation of trophoblastic invasion may play a role. The chorionic plate — the fetal surface formed by trophoblastic invasion — remains smaller than the basal plate, resulting from trophoblastic invasion failing to fully cover peripheral villous structures. Membranes (amnion and chorion) reflect from the basal plate edge toward the chorionic plate edge, folding inward on the fetal surface to form a thickened ring — the 'rolled edge'. Fibrin, organized hematoma, and calcification accumulate at this folding site → forming the thickened ring structure. Peripheral placental tissue (the portion between the basal plate and chorionic plate edge) remains under the membranes with potentially reduced functional capacity. Subchorionic fibrin and hematoma accumulation may disrupt vascular integrity at the placental edge → marginal sinus compression or occlusion → bleeding and abruption risk. In complete circumvallation, the entire placental circumference is affected, potentially significantly reducing functional placental area → IUGR. On US, thickened membranes appear as echogenic, elevated structures at the placental edge — creating a 'shelf' between amniotic fluid and placental surface. On MRI, fibrin and hemosiderin accumulation appears as a low T2 signal ring.
Folding of membranes toward the fetal surface with thickened echogenic ring formation at the placental edge — pathognomonic ultrasonographic finding of circumvallate placenta. Seen around entire circumference in complete form, partially in partial. Subchorionic fibrin/hematoma may accompany.
Folding of membranes toward the fetal surface with thickened echogenic ring formation is seen at the placental edge — 'rolled edge' or 'shelving' sign. The thickened area consists of fibrin and organized hematoma, distinctly thicker than normal thin membranes. Seen around entire placental circumference in complete form, partially in partial form. Difficult to recognize in early pregnancy (1st trimester) when placenta is small — best detected in 2nd trimester.
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Membrane folding toward the fetal surface with thickened echogenic ring at the placental edge is consistent with circumvallate placenta — ___ (complete/partial) form.
Fibrin and/or organized hematoma accumulation is seen in the subchorionic area along the placental margin. Echogenicity depends on age and organization — acute hematoma echogenic, subacute mixed, chronic hypoechoic/anechoic, fibrin deposit usually echogenic. This accumulation is characteristic of circumvallation and reflects disruption of placental edge vascular integrity. Subchorionic hematoma size and extent correlate with bleeding risk.
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Subchorionic fibrin/hematoma accumulation is seen along the placental margin — circumvallate placenta finding.
On T2-weighted MRI, a thickened ring with low signal (fibrin + hemosiderin) is seen at the placental edge. The smaller chorionic plate relative to the basal plate and membrane folding are clearly evaluated on MRI in multiple planes. Subchorionic hematoma can be aged based on T1/T2 signal: acute deoxyhemoglobin (T1 iso, T2 low), subacute methemoglobin (T1 high, T2 variable), chronic hemosiderin (T1/T2 low). Circumvallation extent (complete vs partial) is assessed in coronal and axial planes.
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A thickened ring with low T2 signal at the placental edge is seen on MRI, consistent with circumvallate placenta.
Marginal sinus flow at the placental edge is evaluated on color Doppler. In circumvallate placenta, marginal vascularity may be disrupted — fibrin and hematoma accumulation in the rolled edge region may compress or occlude marginal sinuses → decreased or irregular flow. In normal placenta, marginal sinuses show regular venous flow. This vascular disruption may be the basis of abruption and bleeding pathophysiology.
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Marginal sinus flow at the placental edge has been evaluated on color Doppler; vascularity in the rolled edge region is ___ (normal/decreased/absent).
A 'shelf' formed by chorionic membranes elevated from the fetal surface is seen at the placental edge. This shelf structure represents the angle between the chorionic plate and folded membranes and is a diagnostic finding of circumvallation. Subchorionic fibrin/hematoma may be seen beneath the shelf. Best evaluated on sagittal and axial sections.
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A 'shelf' structure formed by elevated membranes is noted at the placental edge — circumvallation finding.
CT is not typically used as primary modality for circumvallation diagnosis but may be incidentally detected on CTs performed for other indications. Non-contrast CT may show dense calcification ring or fibrin accumulation as hyperdense area at the placental edge. Contrast CT may evaluate placental edge perfusion but indication is limited due to ionizing radiation in pregnancy.
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A hyperdense ring at the placental edge on CT may be consistent with circumvallation — US confirmation is recommended.
Criteria
Circumvallation around entire placental circumference — 360-degree rolled edge
Distinct Features
Significantly higher complication risk — abruption, preterm delivery, IUGR, recurrent 2nd trimester bleeding, effective placental area may be significantly reduced
Criteria
Circumvallation along part of the placental margin — rolled edge in a portion of circumference
Distinct Features
Usually clinically insignificant, low complication risk, may be incidentally detected, specific follow-up may not be needed
Criteria
Membranes pass flat from the edge, no folding — mild form of circumvallation
Distinct Features
Clinically insignificant, unlike circumvallation does not form ring structure, incidental finding
Distinguishing Feature
Subchorionic hematoma collection is usually crescent-shaped in first trimester and not limited to placental edge; circumvallation shows thickened ring-shaped edge detected in second trimester along placental circumference — timing and morphology difference
Distinguishing Feature
Abruption shows retroplacental hematoma with acute painful bleeding; circumvallation edge change is anatomic variant usually presenting with painless or recurrent mild bleeding — location (retroplacental vs subchorionic edge) and clinical presentation difference
Distinguishing Feature
Intervillous thrombosis is a focal intraplacental lesion in the parenchyma not affecting peripheral edge morphology; circumvallation affects placental edge morphology and is not a focal parenchymal lesion — localization difference (parenchymal vs peripheral)
Urgency
routineManagement
surveillanceBiopsy
Not NeededFollow-up
6-monthPartial circumvallation is usually clinically insignificant and does not require specific follow-up — reported as an incidental finding. Complete circumvallation requires increased obstetric surveillance: serial US for fetal growth monitoring (IUGR risk — biometry every 2-4 weeks), AFI measurement, clinical follow-up for recurrent bleeding episodes, attention for abruption findings (retroplacental hematoma, acute painful bleeding). No specific treatment — circumvallation is an anatomic variant that cannot be corrected. Obstetric intervention targets complications: tocolysis for preterm labor threat, early delivery planning for IUGR, emergency cesarean for abruption. Postpartum placental examination definitively confirms the diagnosis — macroscopic rolled edge ring and fibrin accumulation on fetal surface.
Complete circumvallate placenta is associated with increased obstetric complication risk: preterm delivery, IUGR, placental abruption, and perinatal mortality. Partial form carries less risk. After diagnosis, close antenatal surveillance, serial growth US, and fetal well-being assessment are recommended. Diagnosis is confirmed by careful placental inspection at delivery.