At delivery it was noted that the second twin had no clear separation of head, face, neck and trunk. (Fig. 1) There was scanty hair on top. There were no eyes, ears, nose or mouth. Where the eyes are expected there were two skin-coloured nodules, the right one being hemorrhagic. Between them there was a raised bony projection with a shallow midline vertical cleft. There was a ruptured omphalocele, and unrotated small intestine was visible. The upper limbs were undeveloped distally. The male genitalia and lower limbs were comparatively well developed, with talipes. A whole body X-ray showed a malformed mass of bones of the base of skull; there were no cranial, facial, maxillary or mandibular bones; and there were no lungs or heart (Fig. 2).

Fig.1. No separation of head, face, neck and trunk; no eyes, ears, nose or mouth; ruptured omphalocele; hypoplastic limbs.

Fig 2. Base of skull bones are malformed; no bones of the cranium, jaws or face; no heart or lungs; distal limbs hypoplastic.

At autopsy there was no brain. Above the diaphragm there was no heart or lungs, but only two small cavities containing hemorrhagic fluid. The liver, pancreas and spleen were absent. There was no stomach; there were coils of midgut placed centrally, with an appendix, and ending blindly. The kidneys were underdeveloped, measuring only 2 × 1 cm, and there was no ureter or bladder. The penis and scrotum were normal. The upper limbs were very hypoplastic distally, but the lower limbs had rudimentary toes. The placenta was monochorionic and monoamniotic.

The majority of monochorionic twins have placental vascular interconnections. The suggested pathogenesis of TRAP sequence is that a large artery-artery interconnection permits the arterial pressure of one twin to overpower that of the other, and its arterial blood then perfuses the other twin(1). Instead of oxygenated blood flowing in through the umbilical vein and desaturated blood flowing out through the umbilical arteries, desaturated blood from the donor twin flows in through the umbilical arteries of the recipient twin, and returns to the placenta through the umbilical vein. This reversed arterial perfusion with blood that is very low in oxygen and nutrients results in extensive tissue disruption. Since the blood first perfuses the lower segment of the anomalous twin, the lower limbs and scrotum get comparatively more oxygen than the upper segment of the body.

The mother had never undergone antenatal checkup. Prenatal ultrasound examination would have revealed the severe tissue disruption and absence of the brain, heart, and lungs. The differential diagnosis includes macerated twin, amniotic band disruption and teratoma, but doppler imaging of the umbilical cord reveals the pathognomomc reversal of blood flow.

The "normal" twin has a mortality of >50%, due to prematurity, cardiac failure from the excess load, and unexplained sudden death. Prenatal therapy consists of selective delivery of the anomalous twin or hysterotomy to ligate its umbilical cord. Less invasive techniques include fetoscopic umbilical cord ligation(2), laser coagulation of the umbilical cord(3), and coil occlusion of the umbilical artery(4).

Newton Luiz,
Dhanya Mission Hospital,
Potta PO, Thrissur,
Kerala 680 722, India.

1. Jones KL. Smith’s Recognizable Patterns of Human Malformation, 5th edn. Philadelphia, W B Saunders Company, 1997; pp 658-659.

2. Quintero RA, Reich H, Puder K S, Bardicef M, Evans MI, Cotton DB et al. Umbilical-cord ligation of an acardiac twin by fetoscopy at 19 weeks of gestation. New Engl J Med 1994; 330: 469-471.

3. Arias F, Sunderji S, Gimpleson R, Colton E. Treatment of acardiac twinning. Obstet Gynecol, 1998; 91: 818-821.

4. Porreco RP, Barton SM, Haverkamp AD. Occlusion of umbilical artery in acardiac, acephalic twin. Lancet 1991; 337: 326-327.