As usual, our friend and colleague Javier Cortejoso sent us the best and more detailed answer possible!

The following grayscale and color Doppler images demonstrate a tortuous Ductus Arteriosus (Also called Ductal aneurysm):

Grayscale image of a tortuous Ductus Arteriosus

Change in flow direction and increased velocity (aliasing) demonstrated by color Doppler

3-Vessel-Trachea View demonstrating a tortuous Ductus Arteriosus and a persistent Left Superior Vena Cava (LSVC).

The Ductus Arteriosus is a blood vessel segment that connects the main pulmonary trunk to the proximal descending aorta. It plays a vital role in fetal circulation as it allows the majority of the deoxygenated blood coming from the right ventricle to bypass the fetal lungs and join the thoracic aorta. 50% of the blood flowing through the thoracic aorta returns to the placenta (via the umbilical arteries) where oxygenation occurs.

A tortuous Ductus Arteriosus, with an S-configuration, toward the end of gestation (late third trimester) is considered a normal finding with no clinical implications, as Ductus Arteriosus aneurysms resolve spontaneously in postnatal life. Nonetheless, a small group of infants develop complications such as thrombo-embolism, and compression of nearby thoracic structures. Postnatal evaluation is therefore recommended in this group.

Sources:
Abuhamad, A.Z., Chaoui, R. (2016). A practical guide to fetal echocardiography: Normal and abnormal hearts (3rd ed.). Philadelphia, PA: Wolters Kluwer.
Ganesan, S., Hutchinson, D.P., Sampson, A.J. (2015). Prenatal diagnosis of ductus arteriosus aneurysm. Ultrasound, 23(4), 251-253.