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Pathology of twinning   (Marta Ježová)

3  Atlas of fetal pathology

3.2  Pathology of twinning

Marta Ježová

Introduction:

Multiple pregnancy in human is not a physiological event because the anatomy of the human uterus is designed to harbour only one fetus at a time.

Etiology:

Classification:

Pictures

Placenta of biamnial biplacental twins:
Biamnial bichorial placenta, twins, Macro, autopsy (73279)

Another case:
Biamnial bichorial placenta, twins, Macro, autopsy (73280)

Twins and bichorial biamnial placenta:
Placenta, twins, Macro, autopsy (73974)

Bichorial biamnial placenta:
Placenta, bichoriadal biamnial twins, Macro, autopsy (73996)

Clinical signs:

Fetal death in multiple pregnancy:

Suprisingly many pregnancies begin as multiple, but one fetus usually dies sooner than multiple gravidity is recognized (before 10th w.g):

Pictures

Fetus compressus, two placentas with minimal fusion:
Twins, fetus papyraceus, Macro, autopsy (72393)
Twins, fetus papyraceus, Macro, autopsy (72394)
Twins, fetus papyraceus, Macro, autopsy (72395)

Vanishing twin:
Vanishing twin, Macro, autopsy (73072)
Vanishing twin, Macro, autopsy (73073)
Vanishing twin, Macro, autopsy (73074)

Triplets, fetoreduction:
Triplets, fetal reduction, Macro, autopsy (73342)
Triplets, fetal reduction, Macro, autopsy (73343)
Triplets, fetal reduction, Macro, autopsy (73344)

3.2.1  Complications of monochorionic diamnionic placentation

Clinical signs:

  • mortality is 10 – 25%, the highest during the perinatal period
  • growth of the twins depends on the following factors:
    • insertion of the umbilical cord (velamentous or marginal × central)
    • the existence and type of vascular anastomoses between the placentas
    • placental sharing between the twins (may be very unequal)

The fetus with a velamentous umbilical cord insertion and a distinctly smaller area of the placenta, from which it is fed, is in danger of chronic hypoxia, malnutrition and growth retardation. Discordant growth of the twins is a rule in twin transfusion syndrome.

3.2.1.1  Chronic twin transfusion syndrome

Etiology:

There are anastomoses between the circulations of the two fetuses in the monochorionic placenta.

Classification:

Types of anastomoses:

  • arterio — arterial (a-a) superficial
  • veno — venous (v-v) superficial
  • arterio — venous (a-v) deep

Clinical signs:

  • with balanced blood flow in both directions, the fetuses are not in danger
  • if the blood flow is unbalanced, predominantly one way — because of majority of large a-v anastomoses, where the pressure gradient makes the blood flow from the artery into the vein, the effect is that one twin, the donor, has decreased blood volume (hypovolemia), while the other twin, the recipient, has increased blood volume (hypervolemia)
  • neither fetus has optimal conditions for further intrauterine growth, one or both can die
  • this condition usually begins around 20th w.g., 15 – 30% monochorionic diamniotic twins present this syndrome

Consequences:

  • intrauterine death of one or both twins
  • serious intrauterine problems result into premature delivery, high perinatal mortality and morbidity
  • possible intervention:
    • amnioreduction
    • in some cases it is possible to occlude the anastomoses (laser ablation)

Macroscopic appearance:

Clinical signs:

  • Donor:
    • intrauterine growth retardation
    • anemic
    • oligohydramnion (with insufficient renal perfusion the fetus has decreased urinary output)
    • compressed in the uterus by overpressure of the other twin's polyhydramnion, stuck twin
    • deformites of lower limbs
    • often it has a velamentous umbilical cord insertion
  • Recipient:
    • larger fetus, thrives on the expenses of the donor twin
    • plethoric
    • polyhydramnion
    • cardiac hypertrophy as a result volume overload, congestive heart failure
    • hepatosplenomegaly
    • ascites, hydropericardium and hydrops — severe generalized edema
    • usually central insertion of the umbilical cord

Pictures

Chronic twin transfusion syndrome:
Twins, fetofetal transfusion, Macro, autopsy (72409)

Another case of chronic twin transfusion syndrome:
Twins, feto-fetal transfusion, Macro, autopsy (73975)

Case study:

Fetofetal transfusion syndrome
Marta Ježová

History:

Spontanous twin gestation, ultrasound examination in 18th w.g shows two female fetuses, severe fetofetal transfusion, donor — stuck twin, no congenital malformations; recipient with hepatosplenomegaly and also no congenital malformations.

Macroscopic appearance:

  • Twin A — donor:
    • female
    • body weight 152 g
    • body length 21.5 g
    • weight of brain 35.7 g
    • weight of liver 5.5 g
    • weight of heart 0.67 g
    • intrauterine growth retardation
    • bladder and ureter hypoplasia
    • deformites of lower limbs
    • agenesis of the left umbilical artery
  • Twin B — recipient:
    • female
    • body weight 210 g
    • body length 16.5 cm
    • weight of brain 39.5 g
    • weight of liver 16.53 g!
    • weight of heart 2.21 g!
    • urinary bladder dilatation, coiled ureters
    • has both umbilical arteries
  • Placenta:
    • monochorionic diamnionic
    • insertion of the twin septum is distictly asymmetric (oligohydramnion versus polyhydramnion)
    • Twin A (donor): marginal (paraseptal) insertion of the umbilical cord
    • Twin B (recipient): central insertion of the umbilical cord
    • A-V anastomoses were found
3.2.1.2  Acute twin-twin transfusion

Means rapid acute blood loss from the circulations of one twin to the other twin via large superficial anastomoses. This happens most often during delivery. The twins differ in color (anemic versus plethoric) but compared to chronic twin transfusion intrauterine growth is symmetric and also the hearts of these twins are of the same weight.

Acute peripartum transfusion superimposed on chronic prenatal twin transfusion obscures the typical color difference between the donor and the recipient (as described in previous chapter). In such a case the donor looks paradoxically plethoric and the recipient is paradoxicaly pale. The most reliable sign of chronic twin transfusion syndrome is thus heart hypertrophy in recipient. The color or hematocrit levels are rather confusing.

Acute transfusion also occurs in utero after the death of one twin, this means that the surviving fetus bleeds into the circulation of the dead one. Detrimental sequelae in the surving twin:hypoxic/ischemic brain lesions, bowel atresia, aplasia cutis.

Pictures

The chronic recipient is paradoxically anemic, chronic donor is paradoxically plethoric:
Twins, fetofetal transfusion, acute, Macro, autopsy (72419)

Heart hypertrophy, recipient; donor is anemic:
Twins, fetofetal transfusion, paradoxical hyperemia of the donor, Macro, autopsy (72420)

3.2.2  Complications of monochorionic monoamnionic placentation

Clinical signs:

  • extraordinaly hihg mortality 30 – 50%, mostly in utero
  • cord accidents: fratricidal knots or cord entaglement around the neck or limbs, one or both twins may die
  • cord knots and entangelments happen while the fetuses move in the single amniotic cavity
  • anastomoses between the placentas are multiple, usually bidirectional; chronic fetofetal transfusion is rare

3.2.3  Congenital malformations in twins

Clinical signs:

  • single umbilical artery (SUA) is 3 — 4× more frequent than in singleton pregnancies
  • congenital malformations are also more frequent, the numbers given in literature vary
  • one or both fetuses can be malformed (for example anencephaly in commonly seen in one fetus only, while the other twin has no malformation)
3.2.3.1  Chorangiopagus parasiticus (acardius)

Macroscopic appearance:

When blood circulations of twins are connected, a fetus without a functioning heart (acardius) can survive in utero. Acardius can either be a completely amorphous mass or a hydropic object with schematic limbs, trunk and head, but vital organs are not developed (lungs, liver...). Yhe heart is either missing completely or is seriously malformed (univentricular heart etc.). The heart of the healthy twin works for them both (pump twin). This heart hypertrophies, and the fetus may die of congestive heart failure. The acardius has reversed blood circulation (twin reversed arterial perfusion).

3.2.4  Pathology of higher multiple gestations: triplets

Clinical signs:

  • cca 1 : 10 000 of spontaneous conceptions
  • the number has markedly increased with techniques of assisted reproduction
  • triplets may be trizygotic, dizygotic or monozygotic, and so the forms of placentation vary:
    • two fetuses from triplets are commonly monozygotic twins
    • monozygotic triplets are the least frequent, this is explained as resorbtion of the fourth embryo or a delay , asynchronism, in one of the cell divisions, providing that binary divisions stands as the principal rule
    • triplet placenta is described using the numbers of chorions and amnions, for example trichorionic triamnionic, dichorionic triamnionic
  • clinical problems are the same as for twins
  • triplets are always born premature

Pictures

Triplet placenta monochorionic triamnionic and histology of the septum:
Placenta, triplets, Macro, autopsy (72668)
Amniotic membranes, septum, triplets, HE 40x (72651)

Triplet placenta triamnionic trichorial:
Triplets, trichorial triamnial, Macro, autopsy (73345)

Triplets, trichorial triamnial:
Triplets, trichorial triamnial, Macro, autopsy (73346)

3.2.5  Monsters

Monsters are fetuses with marked morphologic anomalies during intrauterine development. Most of these fetuses die either in utero or shortly after birth. Only very rarely does a monster live longer.

Human monsters are very rare. Animal monsters are more frequent.

3.2.5.1  Monstra duplicia

Monstra duplicia form when the zygote does not split completely, therefore the fetus has some body parts once and others twice.

Clinical signs:

  • incidence: 1 : 50 000 – 1 : 100 000
  • 3/4 are female
  • the most frequent form is thoracopagus (shared thorax and thoracic organs)
  • other congenital malformations which are not caused by the fusion in 50% of cases
  • prognosis:
    • depends on the degree of organ sharing, especially the heart
    • stillborn rate is high
    • some types can live a long time, however

Etiology:

Monozygotic twins, late twinning (13 – 14th day after fertilization).

3.2.5.1.1  Gemini monochoriati inequales

Clinical signs:

Distinctly asymmetric twins. One fetus is more or less normally developed, while the other has serious malformations. Whole parts of body may be missing (acardius acephalus, acardius amorphus etc.).

Monozygotic twins share the placenta (chorioamniopagi). In case of asymmetry may the normal fetus be endangered because of shared circulation (microembolism etc.).

3.2.5.1.2  Duplicitas symmetros

Introduction:

Twins are symmetric and relatively well developed, although anomalies are also frequent. Ther are two types of symmetric monsters: disymmetric (planes of symmetry of both parts are at right angles to each other) and monosymmetric.

The difference is that disymetric thoracopagic twins look at each other, while monosymetric twins both look in the same direction.

The possibility for successful surgical separation of such twins depends on the organs shared and other congenital malformations.

Examples: Siamese twins (Chang and Eng Bunker who were xiphopagous) or the Czech Blazek sisters (monosymetric pygopagus).

Classification:

  • Thoracal conjunctions:
    • xiphopagus
    • sternopagus
    • thoracopagus
      • disymmetric form: partially shared trunk, look at each other
      • monosymmetric form: shoulders are fused at angle, arms on the back side may be fused (tribrachius)
      • monosymmetric form has a better prognosis
      • classification according to heart sharing:
        • separate hearts, each in its own pericardium
        • separate hearts sharing one pericardium
        • one heart with atrial union
        • one heart with both atrial and ventricular union
  • Conjunctions involving the head and trunk:
    • prosopothoracopagus
    • cephalothoracopagus
  • Conjunctions involving the pelvis and abdomen:
    • ileoxiphopagus
    • ileothoracopagus
    • pygopagus (dorsal fusion)
  • Monsters with a horizontal axis of symmetry:
    • ischiopagus
    • craniopagus
    • diprosopos
    • dicephalus

Case study:

Thoracopagus
Marta Ježová

History:

  • 11th pregnancy, 7th delivery
  • the mother has not been examined during the pregnancy
  • premature, precipitous labour of the twins
  • vaginal delivery

Macroscopic appearance:

  • male thoracopagus
  • numerous minor external anomalies and internal organ malformations, some of them shared, the others only in twin A:
    • preaxial polydaktyly
    • hypospadia
    • anomalous gothic palate and hypoplasia of the maxila of the fetus A
    • omphalocele
    • esophageal atresia and tracheoesophageal fistula in both fetuses
  • sharing of internal organs:
    • shared liver
    • partially shared intestines — duodenum and small intestine until the omphaloenteric duct
    • shared pericardium
    • shared heart in the shape of a wide letter U, externally fused in the apex region
  • the heart:
    • shared atrium
    • shared ventricles via two muscular defects
      • univentricular heart: left ventricle belongs to the fetus A, right ventricle to the fetus B
      • functionally 4 compartments and 2 rudimental outlet chambers
      • arterial trasposition in fetus A, pulmonary arteries are hypoplastic
      • anomalies of systemic and pulmonary venous return
3.2.5.1.3  Asymmetric dual monsters

These monsters are an analogy to asymmetric twins. One twin (autosite) is well developed and is connected to the other one (parasite), which consists of seriously malformed tissues and organs.

Epignathus parasite is in the oral cavity of the autosite; craniopagus parasiticus is very rare (additional head). A little more frequent is parasitic thoracopagus or xiphopagus. Pygomelus (a limb or finger or some other tissue emerging from the sacral area) is the most frequent type of these malformations.

Parasite can be either external or internal, as a skin-covered cyst (inclusio fetalis).

3.2.5.2  Monstra simplicia

Involvement of one organism only, these are described in the chapter dealing with organ congenital malformations.


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