Succenturiate (accessory) lobe is an additional placental piece separate from the main lobe, supplied by connecting vessels running over membranes. Incidence is ~3-5%, one of the most common placental morphology anomalies. Most are asymptomatic and incidentally detected on prenatal US; however, two important clinical risks exist: (1) if connecting vessels cross the internal os, vasa previa develops — fetal exsanguination risk at membrane rupture, (2) if the accessory lobe is retained at delivery, retention develops → postpartum hemorrhage and infection risk. On US, placental tissue of same echogenicity separate from main lobe + connecting vessels running over membranes between them are seen. Prenatal diagnosis is critically important for vasa previa screening and delivery planning — notification to the delivery team is life-saving.
Age Range
18-45
Peak Age
30
Gender
Female predominant
Prevalence
Uncommon
The succenturiate lobe forms during early embryonic period when the villous tree develops in the decidual layer beyond the main placental disk — some chorionic villi continue developing away from the main implantation site, forming a separate lobe. This may be related to irregular vascularization of the decidual surface during implantation or peripheral limitation of trophoblastic invasion. Vascular connection between main and accessory lobe is maintained by chorionic arteries and veins — these vessels exit the main lobe and run freely over membranes (amnion + chorion) to reach the accessory lobe. The critical difference is: these vessels are not protected by Wharton's jelly (the protective mucopolysaccharide gel in the umbilical cord) nor supported by placental tissue → they are mechanically extremely vulnerable. If connecting vessels cross the internal os, vasa previa develops — at membrane rupture (natural or amniotomy), these unprotected vessels may tear, causing fetal blood loss. Since fetal blood volume at term is only ~250 mL, fatal exsanguination can develop within minutes. During delivery, when the main placental lobe is delivered, the accessory lobe risks being retained — uterine contraction may not separate the accessory lobe. Retained accessory lobe prevents uterine involution, increasing postpartum hemorrhage and infection risk. When the accessory lobe is recognized on prenatal US, connecting vessel course must be fully mapped with Doppler and relationship to internal os definitively determined — this assessment directly affects delivery management.
Placental tissue separate from main lobe + connecting vessels running over membranes (demonstrated by Doppler) — pathognomonic finding of succenturiate lobe. Relationship to internal os determines vasa previa risk; lobe location determines retention risk.
Separate placental tissue of same echogenicity is seen few cm from the main lobe. Between the lobes is a space filled with membranes and amniotic fluid — no placental tissue (villous structure) in this area, only membranes and connecting vessels. The accessory lobe is usually 2-5 cm in diameter, well-defined, and shows identical echogenicity as it has the same villous tissue composition as the main lobe. Lobe size and localization are determined by three-dimensional measurements. Distance from main lobe and relationship to internal os should be reported.
Report Sentence
Separate placental tissue (succenturiate lobe) measuring __ × __ mm is seen __ cm from the main placental lobe — located in the __ (lower uterine segment/lateral/posterior).
Connecting vessels (usually 1-2 chorionic arteries + 1 vein, diameter 2-4 mm) running over membranes between main and accessory lobe are demonstrated on color Doppler. The entire vessel course along membranes is traced and relationship to internal os is definitively evaluated — if vessels cross the os, vasa previa is diagnosed and planned cesarean becomes mandatory. Pulse-wave Doppler confirms flow synchronous with fetal heart rate, differentiating from maternal vessels.
Report Sentence
Connecting vessels running over membranes between main and accessory lobe are demonstrated on color Doppler — relationship to internal os: ___ (not crossing / crossing — vasa previa).
On T2-weighted MRI, placental tissue (same signal intensity — intermediate T2) separate from the main lobe is seen. Connecting vessels may be visible as flow-void (signal loss) due to fast fetal arterial flow — black tubular structures. Amniotic fluid in the space between lobes shows high T2 signal. MRI is complementary in obese patients, posterior placenta, or cases where exact localization cannot be determined by US. Sagittal and coronal planes provide full evaluation of lobe position relative to cavity and os, and vessel course assessment.
Report Sentence
Placental tissue separate from the main lobe is seen on MRI consistent with succenturiate lobe; connecting vessels are demonstrated as flow-void.
A membrane-bridged area between main and accessory lobe is seen — no placental tissue in this area, only membranes and connecting vessels. Amniotic fluid fills this space. This finding differentiates succenturiate lobe from focal placental thickening or continuous formation of bilobed placenta.
Report Sentence
A membrane-bridged area measuring __ cm wide between main and accessory lobe is noted — no placental tissue in this area.
The accessory lobe is usually located in the lower uterine segment or lateral wall; its relationship to the internal os is evaluated. Lower segment lobe carries retention and bleeding risk during delivery — particularly may be in the surgical field during cesarean. Fundal localization of accessory lobe carries lower retention risk but connecting vessels may still cross the os.
Report Sentence
The accessory lobe is located in the ___ (lower uterine segment/lateral/fundal) position, __ cm from the internal os.
CT is not typically a primary modality for succenturiate lobe diagnosis but may be incidentally detected on CTs performed for trauma, pulmonary embolism, or other emergency indications. Contrast CT shows placental tissue with the same enhancement pattern separate from the main lobe. Connecting vessels may be visible as enhancing tubular structures. When incidentally detected, complementary US evaluation is recommended.
Report Sentence
Placental tissue with same enhancement pattern separate from the main lobe is seen on CT, possibly consistent with succenturiate lobe — US confirmation recommended.
Criteria
Connecting vessels do not cross os, no clinical complications
Distinct Features
Vaginal delivery possible, retention risk communicated to delivery team, postpartum placental examination must confirm accessory lobe expulsion
Criteria
Connecting vessels cross the internal os (confirmed by Doppler)
Distinct Features
Planned cesarean MANDATORY (34-37 weeks), amniotomy ABSOLUTELY contraindicated, fetal mortality risk 60% without prenatal diagnosis — drops to <5% with prenatal diagnosis
Criteria
Large accessory lobe (>3 cm), lower uterine segment location, thin connecting vessels
Distinct Features
Special attention notification to delivery team, postpartum placental examination critical, manual removal or curettage if retention develops, potential postpartum hemorrhage and infection
Distinguishing Feature
In vasa previa, vessels cross the os with clinical importance; in succenturiate lobe, vessels may not always cross the os — checked by Doppler, if crossing then diagnoses overlap (succenturiate lobe + vasa previa)
Distinguishing Feature
In previa, placental tissue directly covers internal os; succenturiate lobe may be near os but is separated by membranes and does not cover os with placental tissue — different diagnostic and treatment approaches
Distinguishing Feature
Retention shows postpartum endometrial thickening and vascularity (postpartum diagnosis); succenturiate lobe is diagnosed prenatally (separate lobe + connecting vessels detected on prenatal US) — timing difference
Distinguishing Feature
Chorioangioma is a hypervascular solid mass within/on placenta; succenturiate lobe is a separate lobe with same echogenicity and structure as main lobe supplied by connecting vessels — morphology and vascularity pattern difference
Urgency
routineManagement
surveillanceBiopsy
Not NeededFollow-up
6-monthIn prenatal diagnosis of succenturiate lobe, two critical assessments must be performed: (1) Vasa previa screening — relationship of connecting vessels to internal os must be definitively determined by Doppler; if crossing os, planned cesarean (34-37 weeks) is mandatory, amniotomy is absolutely contraindicated, hospitalization usually recommended at 30-34 weeks. (2) Retention risk notification — prenatal notification to delivery team is required; postpartum placental examination must confirm accessory lobe expulsion, if not expelled then manual removal or curettage (retention = postpartum hemorrhage + infection risk). Without vasa previa, vaginal delivery is possible but retention risk should be considered. Serial US follow-up can monitor connecting vessel position changes (with placental migration) and cervical length. If connecting vessels have moved away from os in 3rd trimester, risk assessment is updated. During delivery, sudden fetal bradycardia + vaginal bleeding combination should suggest vessel rupture → emergency cesarean.
Succenturiate lobe itself is harmless but can lead to three important complications: (1) Vasa previa if connecting vessels cross internal os — fetal hemorrhage at membrane rupture, (2) Retained accessory lobe in uterus at delivery — postpartum hemorrhage and infection, (3) Tearing of connecting vessels — fetal hemorrhage. Prenatal diagnosis is critical for delivery planning — accessory lobe must be checked during placental delivery.