2000-09-02-18 Succenturiate & bilobate placenta © Valero  www.thefetus.net/

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Definition:

The succenturiate placenta is a morphological abnormality, in which there is one or multiple accessory lobes connected to the main part of the placenta by blood vessels¹.  A bilobate placenta is a similar anomaly and it is not clear from the literature what the exact difference if any exist². It appears that some authors use bilobate when both segments of the placenta are almost equal in size (right on the figure) and succenturiate when there is a greater difference (left on the figure). When there is not such a connection, the placenta is called placenta spuria.

^{1 2}

Fig. 1: Succenturiate placenta and bilobate placenta.

Etymology: from the Latin succenturio = to substitute.  

Pathogenesis:

The accessory lobes are vestiges of abnormal distributions of the chorionic villi.

Incidence:

16-28:10,000 pregnancies.

Ultrasound findings:

As on gross morphologic examination, it is possible to see two separate portions of the placenta: the main portion to which the umbilical cord is connected, and the succenturiate lobe. It is important not to confuse this with the placenta that covers two major aspects of the uterine cavity. In the later case, there is a fold of connecting placenta tissue. Sometimes, it is possible that a myometrial contraction can simulate a succenturiate lobe, but in this condition there is no boundary between the lobe and the myometrium and it usually disappears within 30 minutes or less.

 

Differential diagnosis: Occasionally a patient with twins may prematurely deliver one fetus. The obstetrician my then try to maintain the second fetus, and the resulting image is that of a single fetus with 2 placentas. These are complete placenta and the total size is thus greater then the size observed in succenturiate placenta

 

Figs. 2-4: This patient delivered one twin prematurely. The placenta of the miscarried twin is undistinguishable from the placenta of the live twin (even Doppler was not contibutive). Unfortunately the second twin end up aborting 2 weeks later.

Associated anomalies and risks:

The incidence of fetal anomalies is not increased because of the presence of succenturiate placenta. The main risks of this kind of placenta occur at the time of the delivery. Its antenatal recognition is important as vessels connecting the main placenta with the succenturiate placenta may rupture during labor causing fetal dead. In addition, there is an increased postpartum risk of postpartum hemorrhage from retention of placental material^1,3-4.

 Case 1

Figs. 4-6: These are two views of a bilobate placenta, where each of the lobes (one on the anterior and one on the posterior aspects of the uterine cavity) are marked with an *

Case 2

Figs. 7-9: We can see the placenta has two lobes, and the absence of "placental bridge" in between on the third image. Note the similarity fig 2-4.

Case 3

Fig. 10: The two (anterior and posterior) lobes are marked with *

Case 4

Figs. 11-12:  The velamentous insertion of the cord (see also Vasa previa) with branches supplying the anterior and posterior lobes.

Case 5

Figs. 13-19:  In this case not only is the placenta succenturiated, it is also marginal and there is a vasa previa. This fetus was delivered by cesarean section.

Case 6

Figs. 20-22: In this case the main part of the placenta is anterior and the succenturiate lobe (*) is posterior. This kind of placentas are more difficult to see, specially as the pregnancy gets older.

Case 7

Figs. 23-26:    The main part of the placenta is posterior and the succenturiate lobe is anterior.

Case 8

Figs. 27-28:   We can see the posterior placenta and the anterior succenturiate lobe. Also notice the margin between the succenturiate lobe and the myometrium

 

Figs.29-30: Same fetus as in fig. 27-28. Notice on the maternal aspect of the placenta the main part and the succenturiate lobe.

Figs. 31-32: Notice in the fetal aspect of the placenta the insertion of the umbilical cord in the main part of the placenta and the vessels crossing to the succenturiate lobe.

Figs. 33-34: Another example with the pathology specimen and the same specimen"s X-ray after injection of barium in the umbilical vein. Note the absence of vascular connection between the lobes. 

References:

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