Prenatal diagnosis and postnatal findings of cephalothoracopagus, janiceps, monosymmetros twins

Clinical History

A 24-year-old multigravida underwent fetal ultrasound at 24 weeks of gestation for suspected polyhydramnios. Conjoined twins were detected on ultrasound which were delivered by Caesarean section the following week and weighed 1081g. They expired immediately after delivery. Post-mortem CT of formalin preserved specimen was done, which confirmed the ultrasound findings.

Imaging Findings

Prenatal ultrasound showed 2 fetuses with fused head, thorax and abdomen (Fig. 1), with a single umbilical cord with 3 arteries and 3 veins. A single face was noted with low set ears and retrognathia. These findings were confirmed on gross examination of the twins postnatally, which additionally demonstrated 2 partially fused external ears on the opposite side (Fig. 2). Fetal ultrasound and postmortem CT of formalin-preserved specimen showed 2 cerebral hemispheres with an absent corpus callosum, partially fused thalami (Fig. 3), 4 cerebellar hemispheres (Fig. 4), 2 pituitary glands and 4 internal ears (Fig. 5). There were 2 separate hearts with shared circulation (Fig. 6) with one relatively normal heart with persistent left SVC, and one hypoplastic heart (Fig. 7). Two separate livers were noted (Fig. 8). Volume-rendered CT images showed fused cranial vault, 2 unfused spines with partial fusion of the posterior elements of C3 to C5, and 8 limbs (Fig. 9).

Discussion

Conjoined twins are rare variants of monozygotic twins, which result from an incomplete division of a monozygote embryo when the split begins after the first 2 weeks of conception. Conjoined twinning occurs once in every 50, 000–100, 000 births. [1]

Cephalothoracopagus twins with a fused head and thorax but two separate spines, limbs, and pelves is the rarest form with an incidence of once every 3 million deliveries or one per 58 sets of conjoined twins. [2]

Cephalothoracopagus janiceps twins have 2 faces each looking in opposite directions on a single fused head. The face of each fetus is split with each half turned outward, so that each observed face is made up of the right face of one fetus and the left face of the other. Janiceps twins are categorized as disymmetros or monosymmetros based on whether the two faces are symmetrical or asymmetrical, respectively. Monosymmetros twins are associated with a relatively normal anterior face and a rudimentary posterior face. [3, 4]

With the routine use of ultrasound in modern obstetrics, conjoined twins are being diagnosed antenatally, where the role of antenatal ultrasound and MRI is to identify the type of conjoined twins and any associated anomalies, to present a prognosis to the parents to help decide if medical termination of pregnancy should be done, and to assess if surgical separation of the twins would be possible.

Conjoined twins should be ruled out in cases of monoamniotic, monochorionic twins during routine ultrasound. Two-dimensional ultrasound is the primary investigative tool and is sufficient to make the diagnosis. Three-dimensional ultrasound has the advantage of being able to acquire, store and retrieve an entire volume and to display surface and skeletally rendered images. An accurate prenatal diagnosis of conjoined twins can be made by 3D ultrasound as early as at 10 weeks’ gestation. [5, 6] Magnetic resonance imaging can better delineate the shared anatomy in conjoined twins. It is important to identify the site and extent of fusion, the notochordal axes, the number and direction of faces, the number of limbs and the internal anatomy to classify the type of conjoined twins. Marked asymmetry between the two twins should raise suspicion for the possibility of a parasitic twin.

The prognosis of cephalothoracopagus twins is extremely poor and an antenatal diagnosis is an indication for termination of pregnancy. Fetal biometry can help decide the mode of delivery depending on gestational age.

Differential Diagnosis List

Final Diagnosis

Cephalothoracopagus, janiceps, monosymmetros twins.

URL:	https://eurorad.org/case/13628
DOI:	10.1594/EURORAD/CASE.13628
ISSN:	1563-4086