The umbilical cord develops in close association with the amnion and serves a vital function during intrauterine fetal development. Evaluation of umbilical cord entities and function is an integral part of every sonographic examination. It includes cord measurements (diameter of cord vessels as well as estimation of cord length,), analysis of cord anatomy (cord coiling, vessel number), estimations of cord abnormalities capable of impending blood flow and cord function (Cord Doppler).
Abnormalities of the umbilical cord may be related to cord length, diameter, cord coiling, vessel number, cord insertion, anomaly capable of impeding blood flow, funic presentation, and umbilical cord stricture.
Normal cord has 3 vessels: two arteries, one vein encased in Wharton jelly. Two arteries carry deoxygenated blood to placenta, one vein brings oxygenated blood back to fetus. Umbilical vein is the only conduit for oxygenated blood to return to fetus. Umbilical cord is is fully formed by 9 weeks gestation when cord is already coiled, where arteries coil around vein. Abdominal wall insertion is surrounded by intact skin while placental insertion normally centered on placental disc. Clinically, hypo-coiling has been associated with fetal demise, while hyper-coiling is correlated to fetal-growth restriction and intrapartum fetal acidosis and asphyxia. Both entity (hypo & hyper coiling) have been linked to trisomies and single umbilical artery.
Antenatal determination of cord length has technical limitations therefore evaluation of cord diameter use as a predictive fetal marker. The lean umbilical cords have been associated with poor fetal growth while large-diameter cords have been associated with macrosomia. The clinical utility of this parameter is still unclear.
Single umbilical artery (SUA)
Or two vessel cord is associated with growth restriction but if additional anomalies are present then risk for aneuploidy increases. The incidence is increased considerably in women with diabetes mellitus, epilepsy, preeclampsia, antepartum hemorrhage, oligohydramnios or hydramnios. Imaging findings have free loop of cord with 2 vessels seen best on cross section where only one UA is adjacent to fetal bladder. In more than 70% left UA is absent. In addition SUA is bigger than normal UA, almost 15% develop IUGR but are not coupled with trisomy 21.
Umbilical cord cyst (UCC)
Is cyst associated with umbilical cord and may be: Umbilical cord pseudocyst, Allantoic cyst, Urachal cyst, or Omphalomesenteric duct cyst. By definitions it is cyst or cysts associated with umbilical cord with paraxial location (in 60% eccentrically) where umbilical cord vessels are not displaced. It may be seen anywhere along length of cord, with thin walled cyst or cysts, usually anechoic with 2% prevalence. Most often it is transient finding usually as pseudo cysts. However multiple UCC are with increased risk of anomalies and aneuploidy If UCC is near fetal end of umbilical cord it should look at fetal bladder. Allantoic cysts can grow. In different diagnosis UCC may be similar with normal yolk sac or umbilical cord aneurysm or mucoid or cystic degeneration of Wharton jelly or embryonic duct remnants. It has excellent prognosis if transient. Single UCC has better prognosis than multiple UCC. In addition single umbilical cord cysts found in the first trimester tend to resolve completely, whereas multiple cysts may indicate miscarriage or aneuploidy (T18 and T13).
Umbilical cord aneurisms
May be 1) Umbilical vein varix or 2) Umbilical artery aneurysm.
Umbilical vein varix
Is seen as focal dilatation of umbilical vein larger than 9 mm in diameter or larger than 50% of intrahepatic portion of umbilical vein. Best diagnostic clue for UV varix: is cyst-like space in upper abdomen with venous flow on Doppler. Umbilical vein varix in free floating loops of cord is much harder to see. UV varix is usually intra-abdominal but extrahepatic. It may also occur in free-floating loops of cord. Umbilical vein varix is usually seen as upper abdominal "cyst", oval or elongated shape, with thin walled, and anechoic.
It may occur in association with persistent right umbilical vein, may be large, must show continuity of "cyst" and presence of blood flow, usually runs between abdominal cord insertion site and inferior edge of liver with oblique orientation.
Umbilical artery aneurysm
Is dilatation of umbilical artery seen as sacular dilatation of umbilical artery with arterial flow. Umbilical artery aneurism is a rare congenital thinning of the vessel wall with diminished support from Wharton jelly. Aneurysm is usually near placental end of cord, where this support is absent.. UA aneurysm may have arterio-venous fistula to umbilical vein, usually associated with single umbilical artery, associated with multiple anomalies and trisomy 18. Cord "cyst" is near placental origin, wall may be calcified, it is much more rare than UV varix. Finaly it is arterial malformation not venous
Differential Diagnoses: Abdominal cysts (UVA), Umbilical cord cysts (UAV)
Pathology: UV varix may be first manifestation of abnormal venous pressure. Expanding varix in cord may compress umbilical artery
Clinical Issues: Karyotype if other anomalies present, close fetal monitoring, consider early delivery for UV varix.
Capable of Impeding Blood Flow are mechanical and vascular abnormalities of the umbilical cord, capable of impairing fetal–placental blood flow like knots, loops, funic presentation, umbilical cord stricture, hematoma, cysts, thrombosis, vessel dilatation.