Conjoined twins: Morphogenesis of the heart and a review

Abstract

Five cases of conjoined twins have been studied. These included three thoracopagus twins, one monocephalus diprosopus (prosop = face), and one dicephalus dipus dibrachus. The thoracopagus twins were conjoined only from the upper thorax to the umbilicus with a normal foregut. These three cases shared a single complex multiventricular heart, one with a four chambered heart with one atrium and one ventricle belonging to each twin with complex venous and arterial connection; two had a seven chambered heart with four atria and three ventricles. The mono-cephalus diprosopus twins had a single heart with tetralogy of Fallot. The dicephalus twins had two separate axial skeletons to the sacrum, two separate hearts were connected between the right atria with a shared inferior vena cava. Thoracopagus twinning is associated with complex cardiac malformations. The cardiac anlagen in cephalopagus or diprosopus are diverted and divided along with the entire rostral end of the embryonic disc and result in two relatively normal shared hearts. However, in thoracopagus twins the single heart is multiventricular and suggests very early union with fusion of the cardiac anlagen before significant differentiation. Cardiac morphogenesis in conjoined twins therefore appears to depend on the site of the conjoined fusion and the temporal and spatial influence that determines morphogenesis as well as abnormally oriented embryonic axes.

Thoraco-Omphalopagus conjoined twins

“…The present twins also had only a single fourchambered heart and triple-outlet left ventricle. This also distinguishes our case from the other cases of cardiac fusion in conjoined twins reported in the literature; however, the prognosis was not different (1)(2)(3)(4)(5)(6)(7)(8). Our twins died on the first day due to heart failure and progressive metabolic acidosis.…”

“…Thoracopagus conjoined twins have the highest incidence of cardiovascular abnormalities; they may have cardiac abnormalities in any type of fusion, and 90% of these twins share a common pericardial sac. The type of cardiac fusion is a critical factor for mortality (3).…”

Vaginal Delivery of Dicephalic Parapagus Conjoined Twins: Case Report and Literature Review

“…Incidence is 1 : 192,000 in southern Africa, 1 : 33,000 to 1 : 165,000 in North America, 1 : 100,000 in Japan, 1 : 75,000 in Sweden and Latin America, 1 : 68,000 in Hungary, 1 : 14,000 in Africa, and 1 : 6,500 in Taiwan (Castilla et al 1988;Yang et al 1994;Bianchi et al 2000;Gilbert-Barness et al 2003). Increased prenatal detection of CTs with ultrasound may explain an apparent rise in occurrence (Mackenzie et al 2002).…”

“…Increased prenatal detection of CTs with ultrasound may explain an apparent rise in occurrence (Mackenzie et al 2002). Most authors report that 70-95% of conjoined twins are female (Apuzzio et al 1984;Barth et al 1990;Gilbert-Barness et al 2003), although one study cited a nearly equal male: female ratio (Castilla et al 1988). Spencer proposed a parapagus classification for anterolaterally conjoined twins, e.g.…”

“…Past studies describe fused hearts with complex anatomy, including right aortic arch and reversal or transposition of great vessels (Cunniff et al 1988;Hammond et al 1991;Spencer 1992;Itoh et al 1993;Gilbert-Barness et al 2003;Tansel and Yazicioglu 2004). When two hearts are present, the right twin's heart is usually more severely malformed (Spencer 1992).…”