Findings

We knew it was a breech fetus with trisomy 21 and a developing duodenal atresia was best seen on the video.

The question was what is that unusual vessel.

The first image demonstrated that there were 2 vessels side-by-side, one slightly larger than the other one.

The first color image is very important. It shows:

• that the 2 vessels are running side by side,
• in opposite direction (note the colors)
• and to the abdominal wall

The next 3 images demonstrate that the vessel that is in red (carrying blood towards the transducer) is a branch of the aorta, and more important of a caliber very close to that of the aorta.

The blue vessel of image 2 is easy: that is the umbilical segment of the portal vein.

What can the other vessel be ?

Several people suggested that these 2 vessels could represent an arterio-venous fistula and that is certainly an excellent idea. It would have been very unfair to not include a picture of the heart showing right-side enlargement in such case, or other evidence of failure. Among the arterio-venous fistulas that were commonly suggested were hemangioma (90% of the arterio-venous fistula) and arterio-venous malformations. The drainage of these AV malformations is either to the hepatic veins or the portal vein. Although this is difficult to judge there is no great increase of flow to the vena cava (better visible in the clip) or in the liver.

So we are left with a big artery coming from the aorta, having a course that is almost straight postero-anterior, and going along side the umbilical vein to the cord insertion... Described like this it is hard to escape the conclusion: this is a

Replaced umbilical artery to the superior mesenteric artery.

The normal embryology is for the vitelline artery to regress and persist only as the superior mesenteric artery. In this case the left umbilical artery was replaced (which means: improperly connected) to the superior mesenteric artery and the right umbilical artery was in normal position. Replaced umbilical artery to the superior mesenteric artery is very rare in normal fetuses (this baby has trisomy 21) but it is common in acardiac twins and in sirenomelia fetuses[1].

However, there are several reports of complications resulting from the persistence of both the vitelline artery and veins in adults. As can be expected from the embryology, as the secondary yolk sac involutes and is occasionally detected in adults as a Meckel diverticulum, the persistent vitelline arteries and veins usually become symptomatic because the cause intestinal obstructions they cause[2]^{,[3],[4],[5],[6],[7],[8],[9],[10],[11]}.

References

[1] Stevenson RE, Jones KL, Phelan MC, Jones MC, Barr M Jr, Clericuzio C, Harley RA, Benirschke K Vascular steal: the pathogenetic mechanism producing sirenomelia and associated defects of the viscera and soft tissues. Pediatrics 1986 Sep;78(3):451-7

[2] Ebner I, Dohr G Contribution to the significance of persisting embryonic vessels in the adult organism. Anat Anz 1986;162(2):73-8

[3] Miyoshi S, Ikeda M, Kido T, Matsuda Y, Fukada R, Nakajima K, Izukura T Abnormal persistence of the right vitelline vein. J Pediatr Surg 1984 Apr;19(2):204-5

[4] Canavese F, Bardini T Intestinal occlusion caused by remnants of the vitelline artery. Pediatr Med Chir 1983 Jul-Aug;5(4):231-2

[5] Waldschmidt J Intra-abdominal ligament remnants of the vitelline duct and vessels. Monatsschr Kinderheilkd 1983 Apr;131(4):222-7

[6] Raahave D, Bjerre-Jepsen K A vascular band to Meckel"s diverticulum. Ann Chir Gynaecol 1983;72(5):287-8

[7] Reichenbach F Chronic duodenal obstruction caused by a persistent vitelline artery. Zentralbl Chir 1982;107(20):1314-6

[8] Jankowski A Persistent vitelline artery as cause of ileus in a 12-year-old boy. Wiad Lek 1977 Sep 15;30(18):1465-7

[9] Kleinhaus S, Cohen MI, Boley SJ Vitelline artery and vein remnants as a cause of intestinal obstruction. J Pediatr Surg 1974 Jun;9(3):295-9

[10] Myers NA, Rubin S Intestinal abstruction due to a persistent vitelline artery. Aust N Z J Surg 1973 Sep;43(2):161-2

[11] Prust FW, Abouatme J Vitelline artery causing small bowel obstruction in an adult. Surgery 1969 Apr;65(4):716-20