Acardiac twins--an analysis of 10 cases.

The pathological characteristics of the acardiac fetus were studied based on 10 autopsy cases. These cases were collected during a 13-year period at Seoul National University Hospital. All 10 fetuses were monochorionic twins, and six of them were male. Externally normal co-twins survived in five cases and died perinatally in three cases. The gestational period of these acardiacs ranged from 20 to 33 weeks. All of them showed a growth arrest of a fairly wide spectrum. Four cases belonged to acardius anceps, five were acardius acephalus, and one was acardius amorphus. Nine out of 10 cases were holoacardius, whereas one was hemiacardius with a vestigial heart tube present. Characteristic artery-to-artery anastomoses were demonstrated in all cases where examination was possible. The umbilical cords of the acardiacs often consisted of only two vessels, i.e., one umbilical artery and one umbilical vein, and these vessels were directly attached to the arteries and veins of the normal co-twins on the placental surface. The vascular system of the acardiac fetuses was simplified, providing only inflow and outflow pathways through common iliac vessels and vitelline vessels. When the head part was preserved (acardius anceps), the facial features were indistinguishable, particularly in the midfacial region, which resulted in a characteristic holoprosencephalic malformation of the brain in two out of four cases. Normal eyeball structure was not noted in any of these cases. The oral cavity and tongue were rarely recognized. Once the head part was absent (acardius acephalus) there was a wide variation of thoracic organ development. Hypoplastic lungs were seen in three cases, and they were connected to the trachea. A tracheoesophageal fistula was seen twice. The gastrointestinal tract was the most common feature of these acardiac monsters. However, it often lacked some portions, such as a stomach, midgut or part of a large intestine. The kidneys, testes and other parts of the urinary system were other common constituents of the acardiacs.