Doppler in Obstetrics

INTRODUCTION

Color Doppler plays a vital role in the diagnosis of fetal cardiac defects and in the assessment of the hemodynamic responses to fetal hypoxia and anemia. This chapter examines an additional role of color Doppler in the diagnosis of non-cardiac malformations. In the future, color Doppler may also be used in the three-dimensional reconstruction and visualization of fetal and placental vessels.^1,2

PLACENTALAND UMBILICAL VESSELS

The umbilical cord vessels can be followed from their placental insertion (Figure 1) to their attachment on the fetal abdominal wall and their extension into the fetal abdomen ³. Color Doppler is useful in the diagnosis of vasa previa (Figure 2), and targeted examination for this condition should always be undertaken in patients with velamentous insertion of the cord (Figure 1), succenturiate lobe, placenta previa, multiple gestation and amniotic bandss^4–8. Color Doppler is also helpful in the detection of placenta accreta^9,10and chorioangioma, which is an arteriovenous fistulous malformation within the placenta^11,12.

Examination of the umbilical cord facilitates the detection of nuchal cord (Figure 3), false and true knots of the cord (Figure 3), hemangioma or angiomyxoma of the cord, hypoplastic umbilical artery, fusion of two arteries into one, and a single umbilical artery ^13–21. In a transverse view of the lower abdomen, the two umbilical arteries (superior vesical arteries) are seen on either side of the bladder (Figure 4) and, using this plane, it is easier to diagnose a single umbilical artery than by examining a cross-section of the umbilical cord.

A varix or aneurysm of the intra-abdominal part of the umbilical vein is recognized as a hypoechoic cyst and the diagnosis can be made by color Doppler (Figure 5). Color Doppler can also facilitate the diagnosis of an abnormal course of the umbilical vein, including a persistent right umbilical vein (Figures 6 and 7), and absence of the ductus venosus with direct connection of the umbilical vein to the right atrium (Figure 7), inferior vena cava or iliac vein^24-28. In two fetuses with Down syndrome, we detected a fistula between the hepatic artery and the ductus venosus²⁹.



Figure 1: The umbilical cord inserts into an anterior placenta but an umbilical vessel extends into the amniotic membranes (left). In this fetus with a posterior placenta, there is velamentous insertion of the umbilical cord (right).

Figure 2: Transvaginal demonstration of a vasa previa. In this condition, transvaginal color Doppler sonography demonstrates the presence of fetal vessels within the membranes across the internal cervical os (right). The yellow arrows point to the vasa previa and the white arrows to the cervix.


Figure 3: Three-fold nuchal cord (left). False knot of the umbilical cord (right).


Figure 4: Transverse section of the fetal lower abdomen demonstrating the bladder and the umbilical arteries (a). In a fetus with Potter syndrome, there is no visible bladder (?) between the umbilical arteries (b). In this fetus, there is only a single umbilical artery (c).


Figure 5: Transverse section of the fetal lower abdomen demonstrating two cystic structures (a). Color Doppler demonstrates that one cyst is the bladder with both umbilical arteries and the other cyst is a varix of the umbilical vein (b).

In monochorionic twins, color Doppler is useful in the identification of placental vascular communications in pregnancies with twin-to-twin transfusion syndrome, in the detection of retrograde perfusion in twin reversed arterial perfusion (TRAP) sequence and in the diagnosis of cord entanglement in monoamniotic twins ^30,31.

RENAL VESSELS

Color Doppler examination of fetal renal vessels can facilitate the diagnosis of renal malformations. It is best to use a coronal view of the fetus, allowing visualization of the descending aorta with both the left and right renal arteries (Figure 8). Color Doppler is useful in the diagnosis of unilateral or bilateral renal agenesis (Figure 9), double arterial supply of a normal or a duplex kidney (Figure 8), horseshoe kidney (Figure 10) and pelvic kidney ^32-38.


Figure xx: Color Doppler examination of fetal renal vessels , a coronal view allowing the visualization of the descending aorta with both renal arteries(a), unilateral renal artery(b), absence of bilateral renal arteries (c) and absence of bilateral renal arteries + absence of iliac arteries (d).

Figure 6: Persistence of a right umbilical vein (UV) - yellow arrow, which is seen to the right of the stomach (St.)

Figure xx: Ductus venosus agenesis (from Jeanty, 1999)
	Figure 7: Longitudinal view of the fetal trunk and abdomen demonstrating the umbilical vein and ductus venosus in their course through the liver towards the heart.

Figure 7: Example of type 3 ductal agenesis, with the umbilical vein joining directly to the inferior vena cava. (courtesy from Olavarria, www.the fetus.net)


Figure 8: Coronal view of the descending aorta demonstrating both renal arteries (left). Duplex kidney with arterial supply by two renal vessels (right).


Figure 9 Presence of only the right renal artery in a fetus with agenesis of the left kidney (left). In a fetus with bilateral renal agenesis, there are no renal arteries arising from the aorta (right)


Figure 10 Horseshoe kidney diagnosed by real-time ultrasound (left) is confirmed by color Doppler (right)

INTRACRANIAL VESSELS

Color Doppler is helpful in the diagnosis of intracranial arteriovenous fistulae, such as vein of Galen aneurym (Figure-11) and in distinguishing this vascular malformation from an arachnoid cyst, porencephaly or hydrocephaly^39–42. Intracranial arteriovenous fistulae can be also found in other regions of the brain and do not always present as a hypoechoic cyst. In such cases, a fistula is suspected by the presence of the associated cardiomegaly and dilated neck veins, and the diagnosis is made by targeted examination of the brain with color Doppler.

Some malformations of the fetal brain are often associated with an abnormal course of intracranial vessels and their visualization using color Doppler can be used for confirming the diagnosis. Agenesis or dysgenesis of the corpus callosum is associated with an abnormal looping of the pericallosal artery (Figure-12), and, in microcephaly and holoprosencephaly, the shape of the circle of Willis may be distorted (Figure-13)^43,44.




Figure 11 Vein of Galen aneurysm as an intracerebral cystic structure in gray scale (left) and as a vascular malformation with color Doppler (right)


Figure 12 Midsagittal view of the head demonstrating the anterior (pericallosal) cerebral artery in a normal fetus (left). In a fetus with agenesis of the corpus callosum, there is abnormal looping and ramification of the pericallosal artery (right)


Figure 13: Circle of Willis in a normal fetus (left). In holoprosencephaly, the anterior artery is part of the malformation and the circle is not closed (right).

INTRATHORACIC VESSELS

Pulmonary arteries and veins can be seen in their course from the heart into the peripheral pulmonary segments, and Doppler measurements in these vessels may be useful in the detection of pulmonary hypoplasia^45–49. In suspected diaphragmatic hernia, visualization of liver vessels in the thorax can confirm the diagnosis and has prognostic value^50,51.

Color Doppler has also been found to be useful in the diagnosis of the very rare condition of unilateral lung agenesis⁵². In bronchopulmonary sequestration, the diagnosis can be made by the demonstration of the feeding artery arising directly from the descending aorta (Figure-14)^53,54. Some cardiac defects, such as pulmonary valve atresia with ventricular septum defect, are associated with multiple aorto-pulmonary collateral arteries which may complicate the neonatal course.




Figure14: Pulmonary sequestration (a) with the feeding artery arising directly from the descending aorta (b,c). Color Doppler demonstrates that a vessel that arises from the aorta and perfuses the left lung (d,e).

INTRA-ABDOMINAL VESSELS

Color Doppler has made it possible to visualize the celiac trunk with the hepatic, superior mesenteric, splenic, adrenal and other arteries. In general, the differential diagnosis of abdominal wall defects is easy by gray-scale imaging, but, in some cases, color Doppler may be necessary to demonstrate the attachment of the umbilical cord and to help distinguish between an omphalocele and a gastroschisis (Figure 15).

Figure 15:Umbilical vein and ductus venosus in a fetus with exomphalos (left). Gastroschisis with demonstration of the descending aorta, the celiac trunk (ct) and the superior mesenteric artery extending into the exteriorized bowel (right)

Figure 16: Fetus with left isomerism (polysplenia). A cross-section in the upper abdomen shows the stomach (ST) on the right side, no inferior vena cava and the dilated azygous vein near the aorta (left). In the longitudinal coronal view, different flow directions in the aorta and in the azygous vein are demonstrated by color Doppler (right).

However, in these conditions, Doppler measurements in the superior mesenteric artery have not been found to be useful in predicting postnatal outcome⁵⁵. Color Doppler is useful in the diagnosis of hepatic hemangioma, aortic aneurysm, aneurysm of the umbilical vein (Figure 5), and infradiaphragmatic anomalous pulmonary venous drainage^56–58. In fetuses with left isomerism (polysplenia), color Doppler can facilitate visualization of the dilated azygous vein near the descending aorta and confirmation of the absence of the inferior vena cava (Figure 16).

FETAL TUMORS

Fetal tumors are rare but, for optimal perinatal management, their differential diagnosis and precise description are desirable. In fetal goiter, color Doppler demonstrates high perfusion of the thyroid gland^59,60. Echogenic or cystic lesions in the upper part of the kidneys may represent a neuroblastoma, adrenal hemorrhage or congenital adrenal hypertrophy, and the differential diagnosis could be facilitated by visualization of the adrenal arteries by color Doppler^61,62. Color Doppler is also useful in the distinction of sacrococcygeal teratoma, which is vascular (Figure 17), from other cystic lesions, such as meningocele or ectodermal cyst^63,64. A teratoma can also be found in other sites, like the abdomen, thorax or neck. Color Doppler can be used in diagnosing lymphangioma and hemangioma but, in these conditions, flow velocities are very low^65–67.

Figure 17: Vessels within a sacrococcygeal teratoma demonstrated by color Doppler

VISUALIZATION OF FLUID MOVEMENTS

Color Dppler enables not only visualization of blood flow but also movement of fluid. During fetal breathing movements, flow can be observed at the level of the mouth, nose and trachea (Figure 18)^68–70. Color Doppler facilitates the diagnosis of cleft palate by demonstrating the movement of fluid between mouth and nose during breathing movements^71,72. In normal fetuses, there is movement of fluid in the trachea during breathing movements and the flow has been shown to be decreased in those fetuses with diaphragmatic hernia and lethal pulmonary hypoplasia, but not in those that survive⁷³. In laryngeal atresia, there is no fluid flow within the dilated trachea⁷⁴.

In fetuses with duodenal stenosis or atresia, to-and-fro fluid movements can be observed within the stomach (Figure 19), which presumably represent abnormal peristaltic movements. The appearance of this sign may precede the development of the double-bubble sign and polyhydramnios⁷⁵. Similarly, in fetuses with ureteric dilatation and peristalsis, color Doppler may be useful in the diagnosis of vesico-ureteric reflux. In fetuses with suspected genital abnormalities, visualization of urination by color Doppler may help to make the diagnosis of hypospadias.



Figure 18 : Breathing through the nose and mouth in a third-trimester fetus (left). Visualization of the trachea in color Doppler also demonstrates flow. Pulsed Doppler examination allows the demonstration of fluid flow movements during expiration and inspiration (right)


Figure 19: Duodenal atresia with the double-bubble sign of dilated stomach and proximal duodenum (left). Peristalsis and antiperistalsis waves are associated with to-and-fro fluid movements (red and blue) demonstrated by color Doppler (middle and right).


Figure 20: Breathing through the nose in a in a third-trimester fetus with unilateral cleft lip and palate. Image intact lip and palate (a), cleft lip and palate (b) note the flow at the same time inside nostrils and mouth. (c) 3D surface mode unilateral cleft lip and palate.

In fetuses treated with pleuro–amniotic or vesico–amniotic shunts, color Doppler may be useful in demonstrating patency of the shunts and continuing drainage of fluid from the fetus into the amniotic fluid.

DIFFERENTIAL DIAGNOSIS OF OLIGOHYDRAMNIOS

There are essentially three causes of absence or severe reduction in amniotic fluid at mid-pregnancy: premature rupture of the membranes, bilateral renal agenesis or dysplasia, and severe hypoxia with intrauterine growth restriction. Color Doppler is useful in distinguishing between oligohydramnios and anhydramnios, where all the translucent areas in the amniotic cavity are filled with loops of umbilical cord. In hypoxic growth restriction, the fetal measurements are small for gestation, the fetal heart looks dilated and the bowel is echogenic. Doppler demonstrates the presence of two renal arteries and absent or reversed end-diastolic frequencies in the umbilical arteries. In renal agenesis or dysplasia, umbilical artery Doppler is normal, but no renal vessels are seen (Figure 9) and no bladder filling is observed between the intraabdominal umbilical arteries (Figure 4). In premature rupture of the membranes, there are normal renal vessels, normal umbilical flow and normal filling of the bladder.

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