Case of the Week # 516

Case of the Week # 516

Javier Cortejoso
 on 03/18/2023
 on Saturday, March 18th, 2023
The ultrasound images show the following:
• Images 1-4: axial and oblique views of the fetal abdomen identify two anechoic structures, the smallest is 13 x 20 mm. This elongated structure is located in front of the bladder and flow is visualized inside it with color Doppler.
• Images 5-8, videos 1-2: three weeks later, an echogenic round mass that moves freely is observed inside the varix, indicating a possible thrombosis. Color Doppler signals are seen around this echogenic structure. The presence of a bidirectional flow (coded red and blue) indicates that it is turbulent.

Abnormalities of the fetal umbilical vessels are rare, except for single umbilical arteries. Anomalies that can be seen are (1) curvature of the intra-abdominal umbilical vein toward the left-sided stomach due to the persistence of the right umbilical vein, (2) anomalous connection of the umbilical vein in the absence of a patent ductus venosus, or (3) a normal connection but abnormal dilation of the umbilical vein. Aneurysm and varix are both focal dilatations of the umbilical vessels affecting the umbilical artery or vein, respectively. Umbilical vein varix is an uncommon anomaly, representing only 4% of umbilical cord malformations, with a reported incidence of 0.4 to 1.1 in 1000 pregnancies. The diameter of the umbilical vein increases from approximately 2 mm at 15 weeks of gestation to approximately 8 mm at term. Several diagnostic criteria exist for umbilical vein varix: (1) umbilical vein diameter >9 mm, (2) a 50% enlargement of the varix diameter when compared to the diameter of the intrahepatic umbilical vein or (3) a diameter that is more than two standard deviations above the mean for the corresponding gestational age. There are two types of umbilical vein varices, intra-abdominal and extra-abdominal, which is rarely reported. A possible etiology for umbilical vein varix is an intrinsic weakness of the wall of its extrahepatic portion at the site where the right umbilical vein normally obliterates during the embryogenesis.

Sonographically, an umbilical vein varix appears as an oval or elongated fluid-filled mass oriented obliquely in a cephalocaudal direction between the abdominal wall and the inferior edge of the liver. Its continuity with the umbilical vein allows a definite diagnosis of the umbilical vein varix and differentiation from other abdominal cystic masses. Turbulent flow, defined as bi-directional flow on color Doppler sonography, is reported in 28 to 50% of the cases at the level of the dilated segment of the umbilical vein. Kuwata and Matsubara describe the “double bladder sign,” caused by the visualization of two monocystic anechoic masses in the fetal abdomen and pelvis. Color Doppler will reveal blood flow within one mass and no flow in the other mass, which will clarify the diagnosis. Disappearance of the cephalad mass after birth will confirm the clinical diagnosis.

Umbilical vein varix was initially thought to be a serious anomaly with a mortality of up to 44% due to intrauterine fetal death. Certain authors proposed inducing labor at 34 weeks gestation, in spite of the morbidity generated by prematurity. More recently, research has demonstrated improved outcomes, especially if the anomaly is found in isolation. The previously published mortality rate is related to the presence of fetal anomaly, aneuploidy, thrombosis of the varix, cardiac failure due to the increased pre-load, hydrops, intrauterine growth restriction, and neonatal coagulopathy. Some studies report that the outcome of an umbilical vein varix diagnosed before 26 weeks of gestation is worse than one diagnosed later in pregnancy. A recent meta-analysis by di Pasquo in 2018 shows an increased risk of chromosomal abnormalities and intrauterine fetal demise only if there are associated abnormalities. Two mechanisms causing intrauterine fetal death have been proposed: (1) the formation of a thrombus at the level of the dilation creating an obstruction to venous return, and (2) an increase in the cardiac pre-load that may be responsible for heart failure. The diagnosis of a thrombus at the level of the umbilical vein varix is based on the detection of incomplete filling of the vascular lumen on color Doppler sonography, although the clot may also be detected in the form of an intravascular echogenic mass. In this situation, increased fetal vigilance is recommended.

During the 5th week of gestation in normal embryonic development, the embryonic venous system has three pairs of veins: the cardinal veins, the umbilical veins, and the vitelline or omphalomesenteric veins. The last two pairs undergo considerable changes, such that at 10 weeks’ gestation there is a right vitelline vein at the origin of the portal vein, and a left umbilical vein. An anastomosis between the left umbilical vein and the right vitelline vein at an early stage during embryogenesis can occur, and therefore the fetal venous return travels through the vitelline vein in the absence of the umbilical vein. Several cases of antenatal aneurysmal dilatation of vitelline/portal vein have been described, some with thrombosis extending to the portal vein. Early in gestation, this should be suspected when a distinctive anterior-to-posterior downward curvature, rather than an upward direction, is present.

Thrombosis of an umbilical artery may result from extension of an aortic clot as occurs in aortic aneurysms. The occluded artery will appear echogenic and on pathology emboli can be seen in the placenta. The anomaly is not necessarily fatal in fetuses with 3-vessel cord, but is for fetuses with 2-vessel cords.

The differential diagnosis for umbilical vein varix includes normal structures such as a distended gallbladder and fluid-filled segments of the gastrointestinal or urinary tract, and pathological cystic masses such as choledochal, hepatic, mesenteric, duplication, urachal, and ovarian cysts. If flow is noted on Doppler ultrasound examination, non-vascular structures can be eliminated from the differential diagnosis.

Suggested readings:
• Allen SL, Bagnall C, Roberts AB, Teele RL. Thrombosing umbilical vein varix. J Ultrasound Med. 1998 Mar;17(3):189-92. doi: 10.7863/jum.1998.17.3.189. PMID: 9514173.
• Benoist G, Gauthier F, Belloy F, Laloum D, Herlicoviez M, Dreyfus M. Antenatal sonographic features of aneurysmal dilatation of a vitelline vein. Ultrasound Obstet Gynecol. 2007 Jun;29(6):708-11. doi: 10.1002/uog.3993. PMID: 17523163.
• Beraud E, Rozel C, Milon J, Darnault P. Umbilical vein varix: Importance of ante- and post-natal monitoring by ultrasound. Diagn Interv Imaging. 2015 Jan;96(1):21-6. doi: 10.1016/j.diii.2014.01.009. Epub 2014 Mar 13. PMID: 24631035.
• Byers BD, Goharkhay N, Mateus J, Ward KK, Munn MB, Wen TS. Pregnancy outcome after ultrasound diagnosis of fetal intra-abdominal umbilical vein varix. Ultrasound Obstet Gynecol. 2009 Mar;33(3):282-6. doi: 10.1002/uog.6233. PMID: 19115263.
• di Pasquo E, Kuleva M, O'Gorman N, Ville Y, Salomon LJ. Fetal intra-abdominal umbilical vein varix: retrospective cohort study and systematic review and meta-analysis. Ultrasound Obstet Gynecol. 2018 May;51(5):580-585. doi: 10.1002/uog.18895. PMID: 28876490.
• Jain JA, Fuchs KM. Cord Varix. In: Copel JA, ed. Obstetric Imaging. Fetal diagnosis and care, 2nd ed. Elsevier, Philadelphia, PA, 2018; pages 445-448.e1
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• Kuwata T, Matsubara S. Another "double bubble" sign or "double bladder" sign: fetal intra-abdominal umbilical vein varix. J Med Ultrason (2001). 2011 Oct;38(4):243. doi: 10.1007/s10396-011-0321-z. Epub 2011 Aug 16. PMID: 27278592.
• Mahony BS, McGahan JP, Nyberg DA, Reisner DP. Varix of the fetal intra-abdominal umbilical vein: comparison with normal. J Ultrasound Med. 1992 Feb;11(2):73-6. doi: 10.7863/jum.1992.11.2.73. PMID: 1560496.
• Matsumoto Y, Yanai A, Kamei S, Yamaguchi A, Nakamine H, Fujita K. A Case Report of Umbilical Vein Varix with Thrombosis: Prenatal Ultrasonographic Diagnosis and Management. Case Rep Obstet Gynecol. 2019 Aug 6;2019:7154560. doi: 10.1155/2019/7154560. PMID: 31467748; PMCID: PMC6699333.
• Prefumo F, Thilaganathan B, Tekay A. Antenatal diagnosis of fetal intra-abdominal umbilical vein dilatation. Ultrasound Obstet Gynecol. 2001 Jan;17(1):82-5. doi: 10.1046/j.1469-0705.2001.00250.x. PMID: 11244664.
• Viora E, Sciarrone A, Bastonero S, Errante G, Campogrande M. Thrombosis of umbilical vein varix. Ultrasound Obstet Gynecol. 2002 Feb;19(2):212-3. doi: 10.1046/j.0960-7692.2001.00617.x. PMID: 11876820.

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