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a Chapter 31 Doppler Examination of the Fetal Pulmonary Venous Circulation 457
Malformations of Pulmonary Veins
and Their Diagnosis
Fig. 31.14. Simultaneous pulmonary artery and vein Doppler
tracing in a fetus with ectopic beat. The ectopic beat
originating from the atrium is seen as a notching on the
venous side with a reversal flow
contraction is identified by an interruption or a nadir
in venous flow (Fig. 31.13). Using this technique the
examiner is able to easily assess qualitatively the relationship
of atrial to ventricular contraction and to
quantify the arteriovenous time as well. The method
seems to be helpful in differentiating arrhythmias
(Figs. 31.14, 31.15).
Embryology in Summary
Understanding embryologic development facilitates
the comprehension of different anomalies involving
the pulmonary system.
Embryology of the fetal venous system is complex
and has been reviewed several times in the past few
years [20±22] to facilitate the understanding of detected
(mainly intrahepatic) venous anomalies by the
use of color Doppler. The development of the pulmonary
vein system is better examined, since the anomalies
are known entities in pediatric cardiology.
The sinus venosus is incorporated at the end of
the fourth week into the posterior wall of the right
and left atria. The right part of the sinus venosus encircles
the superior and inferior vena cava and becomes
part of the dorsal wall of the right atrium. The
left part becomes remnant and builds the coronary
sinus of the left atrium.
Separately from the development of the left atrium,
the pulmonary veins develop as part of the splanchnic
venous bed. During further development pulmonary
veins differentiate into the individual veins but
still connect to the systemic venous circulation. At a
certain stage these pulmonary veins connect to the
left atrium where a ªcommonº pulmonary vein arises
as a bud and they lose their connection to the central
circulation. It is still debated whether the pulmonary
veins from the lung connect with the bud resulting
from the invagination of the dorsal wall of the left
atrium or with remnants of the coronary sinus [23].
Fig. 31.15. Simultaneous pulmonary artery
and vein Doppler tracing in a fetus
with second-degree arteriovenous block
in connective disease of the mother. For
every second atrial contraction there is
one ventricular systole recorded