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Donor: Dr. Plulau, Montreal Maternity Hospital
Date: 1914
Size (H x W x D cm): 26 x 22 x 12
A normal placenta with attached umbilical cord is seen on the left. Next to it is a markedly malformed fetus, consisting almost entirely of a 鈥渉ead鈥�; no heart was identified.
History: Twenty-one year-old, para 3; triplet pregnancy.
Comment: The condition is more commonly termed the 鈥渢win reversed arterial perfusion (TRAP) syndrome鈥�. It occurs in about 1 in 30,000 pregnancies overall and about 1% of monochorionic twin pregnancies. It is characterised by a normal (鈥減ump鈥�) twin and a twin without a functioning heart (鈥渁cardiac鈥�), each connected to a single placenta. The 鈥減ump鈥� twin provides blood flow to the affected twin via vascular anatamoses. Deoxygenated blood from the acardiac twin returns to the placenta via its umbilical vein and through venous anastomoses traverses to the normal pump twin. Because of increased cardiac flow, the pump twin can develop heart failure.
The cause of the abnormality is not certain. One theory posits a primary developmental abnormality of the fetal heart with secondary dysgenesis of other body parts. A second (and more widely believed) explanation considers the primary event to be development of placental vascular anastomoses with secondary reversal of blood flow from the normal to the abnormal twin. Depending on the specific anastamoses formed, there may be mal-development of the lower limbs, abdomen, thorax and/or head.
CLASSIFICATION OF ACARDIAC FETUSES
Acardius amorphus 聽聽The least differentiated form, in which only bones, cartilage, muscle, fat, and blood vessels are seen. If rudimentary nerve tissue is present, it is called acardius myelantencephalus.
Acardius acormus 聽聽This form lacks a thorax, with the umbilical cord insertion in the head. Despite the absent heart, rudiments of thoracic structures are often found.
Acardius acephalus 聽聽The most common form, with absence of the head, thorax and upper extremities.
Acardius anceps 聽聽These fetuses have a head, thorax and abdominal organs but lack a heart.
Modified from: Bonilla-Musoles F, Machado LE, Raga F, Osborne NG. Fetus Acardius: Two and Three dimensional ultrasonographic diagnoses. J Ultrasound Med 20:117-1127, 2001