Al-Hammadi Hospital, Riyadh, Saudi Arabia.

Case report

A 22-year-old woman (G2P1), with unremarkable history, presented to our unit at 8 weeks and 2 days of gestation. Our ultrasound examination revealed two gestational sacs with uterine cavity. One of the sacs contained live embryo of CRL 20.6 mm (GA 8 weeks+5 days). The second sac, measuring 17 mm, contained just yolk sac with no fetal pole. We'd considered the findings as originally twin pregnancy with vanishing twin in the empty gestational sac.

Another ultrasound was done at 16 weeks and 4 days and revealed cephalothoracopagus twins in one of the gestational sacs. The other sac was empty (11x5 mm).

The cephalothoracopagus twins had two separate spines dividing from the neck, two sets of upper and lower extremities, and one heart.

Images 1, 2: 8 weeks and 2 days of gestation; the images show two gestational sacs - one is empty, the second one contains embryo of CRL 2.06 cm (corresponding to 8 weeks and 2 days of gestation). At the image 2 the embryonic mass has a "V" shape suspected of cephalothoracopagus twins.

Images 3-10: 16 weeks and 4 days of gestation; the images show cephalothoracopagus conjoined twins - one head, common thorax with one heart, two spines dividing from the neck area, two sets of upper and lower extremities and omphalocele.

Images 11-15: 16 weeks and 4 days of gestation; the images show 3D scans of the cephalothoracopagus conjoined twins - one head, common thorax, two sets of upper and lower extremities.

In some cases, the cephalothoracopagus may be mistaken for a singleton fetus due to superposition of the conjoined fetuses and the extreme degree of fusion. Therefore, it is imperative to scan the fetus in different planes. With advanced ultrasound imaging, even earlier prenatal diagnosis of cephalothoracopagus may be feasible. The cephalothoracopagus (or cephalopagus) may appear as "V" shaped embryonic mass during early pregnancy.