Abnormal Umbilical Vessels

Anne Kennedy, MD

DIFFERENTIAL DIAGNOSIS

Common

Single Umbilical Artery
Hypoplastic Umbilical Artery
Velamentous Cord

Less Common

Persistent Right Umbilical Vein
Fused Umbilical Cords
Conjoined Twins
Twin Reversed Arterial Perfusion

Rare but Important

Body Stalk Anomaly
Umbilical Cord Aneurysms
- Umbilical Vein Varix
- Umbilical Artery Aneurysm

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Cord assessment is an important part of all obstetric scans
- Look at abdominal cord insertion site
- Look at placental cord insertion site
- Evaluate cord structure
  - How many vessels are there?
  - Is the cord length normal?
  - Is there an appropriate amount of “twist” to the vessels?
- Follow umbilical vein
  - Normal course of umbilical vein (UV) is to enter left lobe of liver medial to gallbladder
  - UV connects with left portal vein (LPV)
  - LPV connects with inferior vena cava via ductus venosus

Helpful Clues for Common Diagnoses

Single Umbilical Artery
- Seen best on free loop of cord cross-section
- Only 1 artery adjacent to fetal bladder
- Single umbilical artery (SUA) is larger than normal UA (i.e., in a 3-vessel cord)
  - Carries twice the blood volume
- 15% develop intrauterine growth restriction (IUGR)
- Look for additional fetal anomalies
  - 50% risk of aneuploidy if other anomalies in addition to SUA
Hypoplastic Umbilical Artery
- Within spectrum of SUA
- Asymmetry in size of umbilical arteries
- One artery smaller than the other adjacent to bladder
Velamentous Cord
- Submembranous cord insertion (i.e., umbilical cord inserts onto membranes not placental disc)
- Often adjacent to placenta
- Cord vessels are dilated due to lack of support from surrounding tissue
- Submembranous vessels are extremely fragile
- Associated with succenturiate lobe of placenta, placenta previa, twin gestations
- Vasa previa: Submembranous fetal vessels cross cervical os
  - If membranes rupture fetus can exsanguinate
  - 60-80% fetal mortality if diagnosis missed

Helpful Clues for Less Common Diagnoses

Persistent Right Umbilical Vein
- Associated with SUA in most cases
- May be either intrahepatic or extrahepatic
- Intrahepatic: UV passes to right (lateral) of gallbladder (GB) curving toward stomach
  - GB medially displaced
  - GB transversely oriented
  - UV fuses with left portal vein
- Extrahepatic: UV bypasses liver and portal system running anterior to liver
  - Drains into systemic veins
  - Associated with aneuploidy
  - Associated with multiple anomalies
Fused Umbilical Cords
- Abnormal number of cord vessels in excess of the usual 3
  - Most commonly seen with conjoined twins
  - Described in monoamniotic twins where cords fuse proximal to placental insertion site
- Differentiate from cord knot in monoamniotic twins
  - Cord vessels appear to “branch” within the knot
  - In fused cords, the vessels are tubular with the usual helical twist but no entanglement
  - Fetuses may lie close to each other but do not have contiguous skin covering
Conjoined Twins
- Monochorionic twin gestation
- Contiguous skin covering between fetuses
- Variable cord vascular anomalies described
- Most common is fused cord with 6 vessels (2 arteries and 1 vein from each fetus)
Twin Reversed Arterial Perfusion
- Monochorionic twin gestation
- Pump twin structurally normal
- “Acardiac” twin dysmorphic with extensive soft tissue edema
- Single umbilical artery in 66% of acardiac twins
- Hallmark of diagnosis is abnormal direction of flow in UA
  - Normal UA flow is toward placenta, away from fetus
  - In TRAP sequence UA flow is away from placenta, into anomalous fetus

Helpful Clues for Rare Diagnoses

Body Stalk Anomaly
- Absent or very short umbilical cord
  - Vessels seen running between placental surface and fetal torso
- Large thoraco-abdominal wall defect without covering membrane
- Scoliosis is a prominent feature
- Fixed fetal/placental relationship essential for this diagnosis
Umbilical Cord Aneurysms
- Umbilical Vein Varix
  - Focal dilatation of UV > 9 mm diameter or varix diameter 50% > intrahepatic portion of UV
  - Cyst-like space in upper abdomen with venous flow on Doppler
  - Rarely seen in free-floating loops of cord
  - Evaluate with color and spectral Doppler
  - Increasing turbulence on spectral or incomplete filling on color concerning for thrombus
  - Associated with increased venous pressure and hydrops
- Umbilical Artery Aneurysm
  - Saccular dilatation of umbilical artery
  - Usually near placental end of cord
  - Spectral Doppler shows arterial waveform
  - May have arteriovenous fistula to umbilical vein
  - Look for associated anomalies (associated with trisomy 18)

Other Essential Information

SUA may be an incidental finding but may be associated with multiple anomalies
- Careful fetal assessment required for structural malformation
- If additional malformations seen, risk of aneuploidy up to 50%
- Even if no other findings fetus at risk for IUGR
  - Follow up growth in 3rd trimester
- Consider Doppler studies of cord vessels
  - Increased systolic to diastolic ratio associated with increased risk of IUGR

Image Gallery

Ultrasound shows only 2 vessels in the free-floating loops of the cord. The larger vessel is the UV

, and the smaller is the UA

. The fetus was otherwise normal.

Ultrasound, with clinical correlation, shows a 2-vessel cord with a single umbilical artery

wrapping around the vein

(Left) Axial color Doppler ultrasound at the fetal bladder shows asymmetric size of the umbilical arteries

. Three vessels were present in the cord, with one artery significantly smaller than the other. (Right) Axial oblique color Doppler ultrasound shows 2 umbilical arteries adjacent to the bladder