Case of the Week # 506

Case of the Week # 506

Javier Cortejoso
 on 08/14/2023
 on Monday, August 14th, 2023
This is a monochorionic diamniotic twin pregnancy with twin-twin transfusion syndrome causing single twin demise of the donor twin. The images correspond to the surviving recipient twin. The fetal abdominal ultrasound reveals dilatation of several intestinal loops and post-natal X-ray demonstrates a double-bubble sign in the newborn.

Congenital anomalies are a major cause of fetal and neonatal morbidity and mortality. Chromosomal and other genetic abnormalities, environmental teratogens and some nutritional deficiencies account for some congenital anomalies but the majority are of unknown etiology. Peter Pharoah postulates that a significant proportion of congenital anomalies and cerebral palsy of unknown etiology are attributable to a monozygotic multiple conception with monochorionic placentation and early, unrecognized or unrecorded loss of one conceptus (see below). Given the early and comprehensive ultrasound control to which pregnant women are subjected, especially in the developed world, this possibility seems unlikely.

The risk of a congenital anomaly in twin pregnancies is greater than in singleton pregnancies. When anomalies linked to the twinning process are included, the rate of congenital anomaly is 70% greater in a twin than in a singleton pregnancy. This is the case for all congenital anomalies except chromosomal anomalies. Congenital anomalies are almost twice as common in monochorionic twin pregnancies compared to dichorionic twin pregnancies. Sperling et al. assert that a distinction must be made between true structural malformations and sequelae from twin-twin transfusion syndrome.

Monochorionic twins are subject to specific complications which originate in either imbalance or abnormality of the single placenta serving two twins. This unequal placental sharing can cause complications including twin-twin transfusion syndrome (TTTS), twin anemia-polycythemia sequence (TAPS), selective intrauterine growth restriction or twin reversed arterial perfusion sequence (TRAP).

In twin-twin transfusion syndrome (TTTS) the unbalanced blood flow via the placental arteriovenous anastomoses causes hypovolemia / hypotension in one fetus (donor) and hypervolemia / hypertension in another fetus (recipient). This hemodynamic instability can lead to multiple organ damage (particularly the brain), and to fetal demise. In the fetal brain, hypoxic ischemic injury to the white matter supplied by middle cerebral artery can cause extensive multicystic encephalomalacia. Concurrently, hemorrhagic injury may occur in isolation or with concomitant ischemic lesions.

Another possible cause of multiorgan injury of the surviving twin in a monochorionic twin pregnancies is single twin demise. This can trigger exsanguination of the survivor into the demised twin through the placental vascular anastomoses. This can lead to demise of the surviving twin in 20% of cases or lead to the development of ischemic lesions in various organs (mainly the brain) in another 20% of cases.

Structural defects that have been reported in children whose monozygotic co-twin died in utero may be the result of vascular disruption of a previously normally formed structure. Those that have been described are mainly nervous system defects (multicystic encephalomalacia, porencephaly, hydranencephaly, cerebellar necrosis, hydrocephalus, microcephaly, and spinal cord transection). Gastrointestinal (small bowel atresia, colonic atresia, perforation and necrotizing enterocolitis), renal (renal cortical necrosis, renal agenesis, and horseshoe kidney), cutaneous (aplasia cutis congenital), craniofacial (hemifacial macrosomia), and terminal limb defects have also been described. Pharoah has proposed three possible mechanisms of fetal damage in monochorionic twins:
a. Embolic theory: thromboplastin-like material or emboli are transferred through an open placental anastomosis from the dead fetus to the survivor.
b. Ischemic theory: blood is shunted from the survivor into the low resistance circulation of the dead fetus.
c. Hemodynamic instability theory: bidirectional shunting leads to ischemic damage affecting either or both fetuses.

Neither thromboembolism nor disseminated intravascular coagulation has been demonstrated in these cases. The third mechanism may occur with either the demise of one or both twins, or the survival of both twins. The clinical outcome will depend on the severity (fetal death, infant death, congenital anomaly, normality), site (which organ(s) are affected) and timing (early, middle or late in gestation as demonstrated by the brain pathology) of the event.

Intestinal atresia and/or perforation in both recipient and donor twins has been reported in connection with TTTS, usually after laser therapy, which suggests an embolic phenomenon after laser coagulation of the communicating vessels. Furthermore, the other two theories may explain the occurrence of intestinal atresia in this case, as fetoscopic laser ablation was not performed.

Bowel dilatation is usually related to mechanical obstruction with associated polyhydramnios. Differential diagnosis includes mid- and hindgut atresia, imperforate anus, meconium ileus due to cystic fibrosis, intestinal malrotation, volvulus and peritoneal bands. The diagnosis of intestinal dilatation does not necessarily imply obstruction of the gut, since non-obstructive conditions, such as congenital chloride diarrhea and Hirschsprung’s disease have been reported with bowel dilatation. The most important etiologic factor of necrotizing enterocolitis is intestinal ischemia, or hypoperfusion leading to altered mucosal integrity.

Suggested readings:
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7. Patel S, Randolph LM, Benirschke K, et al. Prevalence of noncardiac structural anomalies in twin-twin transfusion syndrome. J Ultrasound Med 2012; 31: 555-560
8. Pharoah POD. Causal hypothesis for some congenital anomalies. Twin Research and Human Genetics 2005; 8: 543-550
9. Saura L, Muñoz ME, Castañón M, et al. Intestinal complications after antenatal fetoscopic laser ablation in twin-to-twin transfusion syndrome. J Pediatr Surg 2010; 45: E5-E8
10. So PL, Li KW, Yeung TW, Sin WK. Multicystic encephalomalacia and gastrointestinal injury following single fetal death in first trimester and subsequent fetofetal transfusion syndrome in a monochorionic triplet pregnancy: a case report. BMC Pregnancy Childbirth. 2019; 19: 311
11. Sperling L, Kiil C, Larsen LU, et al. Detection of chromosomal abnormalities, congenital abnormalities and transfusion syndrome in twins. Ultrasound Obstet Gynecol 2007; 29: 517-526
12. Tsukimori K, Yumoto Y, Masumoto K, et al. Ischemic ileal perforation in the donor of monochorionic twins complicated by twin-twin transfusion syndrome. Fetal Diagn Ther 2009; 26: 173-176

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