Sonographic Assessment of the Umbilical Cord

Abstract

The umbilical cord (UC) is a vital connection between fetus and placenta. It constitutes a stable connection to the fetomaternal interface, while allowing the fetal mobility that is of great importance for fetal development in general and fetal neuromotor development in particular. This combination of mechanical stability and flexibility is due to the architecture of the UC. There is however a range of umbilical cord complications that may be life threatening to the fetus and these too can be explained to a large extent by the cord's structural characteristics. This review article discusses clinically relevant aspects of UC ultrasound.

Keywords: fetal period; ultrasound; umbilical cord.

Fig. 1 a

and b Schematic representation of the early phase of UC development (adapted from www.embryology.ch). b Development of the UC after it is enveloped by amnion (details in text). Caption: yolk sac (*), allantois (‡), red: ectoderm/amnion, yellow: mesoderm, green: extra-embryonic coelom/chorionic cavity.

Fig. 2 a

to d Ultrasound findings in the body stalk anomaly. a Short umbilical cord. b Partial extraamniotic position of the fetus: the upper body is surrounded by the circular depicted amnion, while the lower body lies outside of the amnion. c 3D surface image of the same fetus as in b. A large abdominal wall defect is visible with herniation of liver (→) and intestine (*). The amnion can also be seen (▸) – it extends up to the abdominal wall defect. d Scoliosis in a different fetus with body stalk anomaly.

Fig. 3 a

and b Normal umbilical cord insertion. a Demonstration of the cord insertion and a number of chorionic plate vessels. Depending on fetal lie visualisation may be difficult even if the placenta is anterior. For further differentiation it may be helpful to examine the placenta tangentially as in b. The star-like pattern of the chorionic plate vessels as they approach the cord insertion is seen. Placental tissue surrounds them. The yellow line in a represents the level and orientation of the image in b.

Fig. 4 a

to d Pathological cord insertions. a Velamentous insertion at the end of the first trimester. The UC insertion is demonstrable opposite the chorion frondosum. b Transvaginal view of the same pregnancy as in a. A velamentous vessel runs directly across the cervical os (≙ vasa praevia). c and d Demonstration of velamentous vessels in the second trimester: c Longitudinal section. d Transverse section. These findings must always be followed by further assessment of placental UC insertion (to exclude velamentous insertion) and examination of the lower uterine segment (to exclude vasa praevia). Caption: chorion frondosum/placenta (*); cord insertion (→); cervical canal (▸).

Fig. 5 a

to d Cystic segment of UC in cross section (a und b), and in longitudinal section (c und d). Cysts can be differentiated from perfused vessels using Doppler ultrasound (b und d). Despite the cystsʼ segmental occurrence and irregular shape, both characteristic of pseudocysts, differentiation is only possible on histology. This fetus also had agenesis of the septum pellucidum, schizencephaly and atrioventricular valve incompetence.

Fig. 6 a

to d  a and b Demonstration of an UC cyst in a central cord segment in the first trimester; c and d Fetus with a large UC cyst located at the fetal cord insertion. The echogenic appearance of the cyst margin nearest the abdominal wall (▸) raises the suspicion of an abdominal wall defect. An omphalocele was subsequently diagnosed. Caption: yolk sac (*).

Fig. 7 a

to d  a Perivesical course of the UAs right up to the fetal cord insertion. b Cross section of a normal umbilical cord. The three vessel lumens appear as a stylized Mickey Mouse. c Demonstration of two UAs in their perivesical course in the first trimester up to the fetal cord insertion. d Due to their close proximity in the first trimester, the UAs may be confused with the femoral arteries (▸). Caption: urinary bladder (*).

Fig. 8 a

to d Single umbilical artery. a and b SUA in the second trimester– perivesical (a) and in cross section (b). c and d SUA in the first trimester, perivesical – a low pulse repetition frequency and high colour gain are recommended to assist in differentiating vessels from the nearby femoral arteries (▸) (vessel course all the way to the fetal cord insertion – for comparison, see also Fig. 7 c und d). Caption: urinary bladder (*).

Fig. 9 a

and b Normal anatomy: intraabdominal course of the UV and union with portal system. Green lines in section a show the tangential course of the arching vessel with respect to the fetal stomach (*). The left portal vein branch (▸) and ductus venosus (→) are visible. In section b a colour change allows identification of the ductus venosus (“aliasing” caused by flow acceleration). Caption: hepatic veins (‡).

Fig. 10 a

and b Persistent right umbilical vein (PRUV). The vascular arch runs towards the stomach (see Fig. 9 for comparison). The gallbladder (→) lies medially to the right UV. Caption: stomach (*).

Fig. 11 a

and b Umbilical vein varix with a diameter of 11.6 mm. Turbulent flow within the outpouching/vessel dilatation is shown on Doppler ultrasound.

Fig. 12 a

to d Convoluted umbilical cord in a monoamniotic twin pregnancy. a Demonstration on ultrasound. b Macroscopic view of tangled umbilical cords. c and d Doppler ultrasound assessment of tangled umbilical cords. Two independent curves are seen in parallel (fetus 1 and fetus 2).