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International Journal of Gynecological Pathology:
Original Contributions

Vascular Anastomoses in Dichorionic Diamniotic-Fused Placentas

Foschini, Maria P.; Gabrielli, Liliana; Dorji, Tshering; Kos, Marina; Lazzarotto, Tiziana; Lanari, Marcello; Landini, Maria P.

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From the Departments of Anatomic Pathology (M.P.F., T.D.), Ospedale Bellaria, Preventive Pediatrics and Neonatology (M.L.), and Clinical and Experimental Medicine (L.G., T.L., M.P.L.), Section of Microbiology, University of Bologna, Bologna, Italy; and the Department of Gynecologic and Perinatal Pathology (M.K.), Clinical Hospital Center Zagreb, Croatia.

Address correspondence and reprint requests to Maria P. Foschini, Anatomia Patologica, Ospedale Bellaria, Via Altura, 3, 40139 Bologna, Italy.

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Abstract

A case of fetal twin-to-twin cytomegalovirus infection through a dichorionic diamniotic (DiDi)-fused placenta prompted our search for possible vascular anastomoses in this type of placenta. This case and three additional DiDi-fused placentas were studied with gross (macro) sections and a three-dimensional (3D) stereomicroscopic technique. Two twins were dizygotic (they differed in gender and blood groups) and the other two were probably monozygotic. Macrosections and 3D-image analysis demonstrated side-to-side connections between small subchorionic vessels. These findings demonstrate that vascular anastomoses are present in DiDi-fused placentas.

Vascular anastomoses in placentas of twin fetuses are well described in cases of diamniotic monochorionic (DiMo) and monoamniotic monochorionic (MoMo) placentas, in which they constitute an important prognostic factor for the outcome of multiple pregnancies (1). Vascular anastomoses have only rarely been described in diamniotic dichorionic (DiDi)-fused placentas (2–4). Recently we observed a case (propositus case) of fetal twin-to-twin cytomegalovirus (CMV) infection through a DiDi-fused placenta. Although amniotic fluid collected at the 21st week of gestation indicated CMV infection in only one baby, evidence of CMV infection was present in both babies at birth (5). This observation prompted our search for possible vascular anastomoses in DiDi-fused placentas.

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MATERIALS AND METHODS

Three DiDi-fused placentas, all with centrally inserted umbilical cords, were selected and studied with the propositus case. In all cases, blood group and gender were recorded to determine the zygosity of the fetuses. All of the placentas were formalin-fixed and serially sectioned perpendicular to the intervening membranes. Sections 3 to 5 mm in thickness were cleared for three-dimensional (3D) stereomicroscopic examination, a method similar to that introduced in 1973 by Wellings and Jensen (6) for the study of breast tissue. This method allows direct tracing of blood vessels visible because of the presence of luminal erythrocytes. Sections were washed overnight in distilled water, dehydrated for 2 hours in 70% alcohol followed by three changes in absolute alcohol of 2 hours each. After the last change, the specimens were placed in a solution containing equal volumes of absolute alcohol and xylol for 1 hour and then were finally cleared in xylol for 1 hour. The sections were then immersed in methyl salicylate and examined using a stereomicroscope. Areas with vascular connections were selected and paraffin-embedded for histologic examination. A parallel macrosection was embedded in paraffin for assessment of the full-thickness placental histology. In addition, small blocks for conventional histology were obtained both from the intervening membranes and the shared chorion.

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RESULTS

Two pairs of twins were dizygotic; the first twins differed in gender and blood group (female 0 Rh+ and male A Rh+) and the second twins differed only in blood group (female, 0 Rh+ and 0 Rh−). Although there is no definitive proof of the DNA fingerprint pattern, the other two pairs of twins were likely monozygotic, being of the same gender and having the same blood group. The third twins were both AB (Rh+) females, whereas the fourth twins were both O (Rh+) females. On macroscopic examination, all cases showed normal umbilical cords with central insertions. Macrosections showed that the sides of the two placentas were fused. The intertwin septum in each case was composed of two amnionic layers with an interposed zone of chorionic tissue (Fig. 1). Three-dimensional stereomicroscopic examination allowed direct visualization of the subchorionic vessels. Occasional small blood vessels in the subchorionic layer, visible because of the presence of luminal erythrocytes, extended from one side to the other (Fig. 2a). The subchorionic vessels from both sides branched and converged into rare, small, glomerular-like structures (Fig. 2b) that formed small connections (shunts) between two adjacent branching vessels. Histologic examination of the same section showed that the vessels divided and branched into small capillaries in one single cotyledon (Fig. 2c).

Fig. 1
Fig. 1
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Fig. 2
Fig. 2
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DISCUSSION

Three-dimensional stereomicroscopic techniques have so far been applied mainly to the study of breast pathology, providing important information on the origin of ductal carcinoma in situ and its extension within the ductal tree (6,7). To the best of our knowledge, this method has never been applied to placental tissue. The method described in this article allows direct visualization of the subchorionic vessels.

Vascular anastomoses in placentas have been previously studied by injecting ink into the blood vessels and by corrosion techniques (8–10). These studies demonstrated that DiMo and MoMo placentas were endowed with multiple vascular anastomoses between large arteries and veins and between capillaries (8,9). The initial data on vascular shunts observed in DiDi-fused placentas were controversial, because they were based on corrosion techniques that compromised morphologic examination of the placenta (10). Unlike previous studies, our 3D observations were based on direct observation of vessels containing erythrocytes. All cases of DiDi-fused placentas that we studied had rare subchorionic vascular anastomoses confined to the small vessels. Rare vascular anastomoses also were present in the two placentas from probable dizygotic twins. Previous observations suggested that vascular anastomoses occur in a small proportion of DiDi-fused placentas (10). On the contrary, although our study is limited to a small number of cases, direct visualization suggests that vascular anastomoses, albeit rare and small, might be present in many cases of DiDi-fused placentas. These findings might explain twin-to-twin CMV infection, the rare cases of blood chimerism, and twin-to-twin transfusion observed in fraternal twins (2,3,5,11,12).

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Acknowledgments:

The authors thank Prof. Vincenzo Eusebi for critically review of the article and Massimo Romagnoli for photographic help.

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REFERENCES

1. Bajora R, Wee LY, Anwar S, et al. Outcome of twin pregnancies complicated by single intrauterine death in relation to vascular anatomy of the monochorionic placenta. Hum Reprod 1999; 14:2124–30.

2. King AD, Soothill PW, Montemagno R, et al. Twin to twin blood transfusion in a dichorionic pregnancy without the oligohydramnios: polyhydramnios sequence. Br J Obstet Gynaecol 1995; 102:334–5.

3. French CA, Bieber FR, Bing DH, et al. Twins, placentas and genetics: acardiac twinning in a dichorionic, diamniotic, monozygotic twin gestation. Hum Pathol 1998; 29:1028–31.

4. Lage JM, Vanmarter LJ, Mikhail E. Vascular anastomoses in fused, dichorionic twin placentas resulting in twin transfusion syndrome. Placenta 1989; 10:55–9.

5. Gabrielli L, Lazzarotto T, Foschini MP, et al. Horizontal in utero acquisition of cytomegalovirus infection in a twin pregnancy. J Clin Microbiol 2003; 41:1329–31.

6. Wellings SR, Jensen HM. On the origin and progression of ductal carcinoma in the human breast. J Natl CancerInst 1973: 50:1111–8.

7. Foschini MP, Tot T, Eusebi V. Large section (macrosection) histologic slides. In: Silverstein MJ, ed. Ductal Carcinoma In Situ of the Breast. 2nd ed. Philadelphia: Lippincott Williams & Wilkins, 2002.

8. Bhargava I. Blood vessels of the twin placenta, in relation to zygosity. Acta Genet Med Gemellol 1976; 25:121–4.

9. Bhargava I, Chackravarty A. Vascular anastomoses in twin placenta and their recognition. Acta Anat 1975; 93:471–80.

10. Fox H. The placenta in multiple pregnancy. In:Pathology of the Placenta. 2nd ed. Major Problems in Pathology. London: WB Saunders, 1997:77–101.

11. Benirschke K. Multiple gestation, incidence, etiology and inheritance. In: Creasy RK, Resnik R, eds. Maternal Fetal Medicine. Principles and Practice. London: WB Saunders, 1984:511–26.

12. Molnar-Nadasdy G, Altshuler G. Perinatal pathology casebook. A case of twin to twin transfusion syndrome with dichorionic placentas. J Perinatol 1996: 16:507–9.

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This article has been cited 4 time(s).

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Keywords:

Placenta; Diamniotic dichorionic; Vessel; Twin

©2003International Society of Gynecological Pathologists

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