Discussed by Philippe Jeanty

This is a very interesting case for many reasons:

Interesting embryology,

Another of those example where a casual look might miss the finding, and finally

One of those rare anomalies where the diagnosis can be obtained mainly through reasoning.

Actually I was very tempted to only include a single image, but since Peter was generous enough to give two images... those who want some additional help can use the image on the right (or bottom depending on your screen resolution)!

Finding

Many have found that the abnormal finding was that the inferior vena cava was too large.

The only reasons why the vena cava can be too large are limited to:

• Slowing of the flow
• Increase in flow

Slowing of the flow: A slowing of the flow could have resulted in a widening of the vessel. Many anomalies that could have resulted in a slowing of the flow were submitted and most involved right-sided obstructions: atrio-ventricular valve atresia, endocardial cushion defect, univentricular hearts, regurgitation, atrial myxoma... Although atrial myxomas are generally considered to not occur in fetuses and have not been diagnosed prenatally there are at least 2 cases of neonatal diagnosis[1],[2], and it is therefore just a matter of time until one is diagnosed prenatally.

If the inferior vena cava was enlarged because of an obstruction one would expect that other signs of right-heart failure would also be present. Yet these images show no evidence of ascites.

Increase in flow: How could the flow be increased in the inferior vena cava? The most common reason for increase in flow is that there is a shunt before the vena cava and that the increase in blood flow through the shunt results in an increase of flow in the vena cava. The three most common shunting lesions in the fetus are the vein of Galen aneurysm, chorioangioma and hepatic angioma. All three would have resulted in a increase of flow above the level of the vena cava that is seen on the images. Further, a shunting lesion would also have enlarged the aorta, a finding that was no present.

Another cause of increased blood flow is the detour of a normal flow via the inferior vena cava. The most common reason for that is an aberrant connection of the umbilical vein into the iliac vein in case of ductal agenesis. The blood flow is thus increased in the inferior vena cava at the expense of the flow through the liver.

It is always difficult to demonstrate the absence of "something" on ultrasound, but the axial section did not demonstrate the usual portal vein.

Ductus venosus agenesis

Absence of the ductus venosus is not common. The return of the umbilical flow is via various vicarious ways[3],[4]:

• a suprahepatic connection to the inferior vena cava or
• rarely to the right atrium directly[5],[6]
• an infrahepatic connection to the inferior vena cava,
• a cutaneous anastomosis with formation of a caput medusa
• an iliac connection. an iliac connection.

1: The normal umbilical vein to portal vein with the ductus; 2: the suprahepatic connection to the inferior vena cava; 3: the infrahepatic connection to the inferior vena cava; 4: caput medusa in cutaneous anastomosis; 5: the iliac connection; 6: Connection to the right atrium

The typical ultrasound finding is that of the absence of the connection of the umbilical vein into the portal vein. The other findings of course depend on the type of connection. In the iliac connection, the umbilical flow returns to the iliac vein and thus to the inferior vena cava

Associated anomalies

None but it may be associated with aneuploidies[7], focal liver necrosis and calcifications6, diaphragmatic hernia[8], hydrops and cardiovascular anomalies[9],[10],[11].

An interesting point of physiology, in these fetuses, is that the normal streaming of the flow that occurs in the inferior vena cava, does not occur. That streaming separates the oxygenated and deoxygenated blood that reaches the heart.  These fetuses may thus go into cardiac failure and develops hydrops.

Teaching point

The presence of a large inferior vena cava is very suggestive of agenesis of the ductus venosus with vicarious connection to the iliac vein. Check the portal circulation when in doubt.

References

[1] Dianzumba SB, Char G Large calcified right atrial myxoma in a newborn. Rare cause of neonatal death. Br Heart J 1982 Aug;48(2):177-9

[2] Yamazaki N, Okabe M, Tanaka K, Yada I, Yuasa H, Kusagawa M, Soga T A case of right atrial myxoma in a newborn infant. Kyobu Geka 1986 Jan;39(1):68-70

[3] Moore L, Toi A, Chitayat D Abnormalities of the intra-abdominal fetal umbilical vein: reports of four cases and a review of the literature. Ultrasound Obstet Gynecol 1996 Jan;7(1):21-5

[4] Avni EF, Ghysels M, Donner C, Damis E In utero diagnosis of congenital absence of the ductus venosus. J Clin Ultrasound 1997 Oct;25(8):456-8

[5] Yoshinaga K, Kodama K Persistence of the hepatic segment of the left inferior vena cava in man and its relation to the ductus venosus development. Acta Anat (Basel) 1997;160(2):132-8

[6] Cohen SB, Lipitz S, Mashiach S, Hegesh J, Achiron R In utero ultrasonographic diagnosis of an aberrant umbilical vein associated with fetal hepatic hyperechogenicity. Prenat Diagn 1997 Oct;17(10):978-82

[7] Gembruch U, Baschat AA, Caliebe A, Gortner L Prenatal diagnosis of ductus venosus agenesis: a report of two cases and review of the literature. Ultrasound Obstet Gynecol 1998 Mar;11(3):185-9

[8] Strouse PJ, Di Pietro MA, Barr M Jr  Pitfall: anomalous umbilical vein and absent ductus venosus in association with right congenital diaphragmatic hernia. Pediatr Radiol 1997 Aug;27(8):651-3

[9] Cayol V, Braig S, Noto S, Jannet D, Bouillie J, Marpeau L, Milliez J Agenesia of the canal of Arantius. A case report. J Gynecol Obstet Biol Reprod (Paris) 1997;26(4):430-4

[10] Siven M, Ley D, Hagerstrand I, Svenningsen N Agenesis of the ductus venosus and its correlation to hydrops fetalis and the fetal hepatic circulation: case reports and review of the literature. Pediatr Pathol Lab Med 1995 Jan-Feb;15(1):39-50

[11] Jorgensen C, Andolf E Four cases of absent ductus venosus: three in combination with severe hydrops fetalis. Fetal Diagn Ther 1994 Nov-Dec;9(6):395-7