Case of the Week # 522

Case of the Week # 522

Javier Cortejoso
 on 03/25/2023
 on Saturday, March 25th, 2023
The ultrasound images show the following: In the right ventricular outflow tract, a path to the left of the ductus arteriosus can be seen, with a mild dilation of the same. At a slightly higher level, three-vessel view shows a rounded lateral protrusion of the ductus arteriosus. With color Doppler, it is possible to observe turbulent flow at this level.

The ductus arteriosus (DA) is one of the most important vessels of the fetal circulation. It emerges from the bifurcation of the main pulmonary artery, thereby connecting the right ventricular outflow tract with the descending aorta. The ductus arteriosus is a vital component of the fetal circulation, diverting blood flow away from the pulmonary vascular bed and the non-ventilated lungs. Approximately 75% of the blood flow from the pulmonary artery flows through the ductus arteriosus to the descending aorta, while only 25% flows to the pulmonary arteries. The ductus arteriosus is described as a straight channel from the main pulmonary artery to the descending aorta. The normal diameter of the ductus is equal to that of the descending aorta. Morphometric studies reveal an increase in ductal diameter throughout gestation, with a slightly greater diameter at the aortic end of the arterial duct. Many authors highlight the importance of the three-vessel view in depicting the arterial duct and its abnormalities.

An incremental tortuosity of the ductus with advancing pregnancy has been established. Early in gestation, the 2-dimensional echocardiographic high transverse thoracic view shows the ductus arteriosus as a straight channel from the main pulmonary artery to the descending aorta. As gestation progresses, the ductus normally curves to the left, away from the aortic arch. Benson et al noted that 56% of fetuses had a marked curvature in the late third trimester compared to only 2% in the late second trimester. This marked curvature is accompanied by a configuration that can be either a sharply angled C-shape or an S-shape. During fetal breathing it is possible to observe that the ductus arteriosus bends, producing a more concave arch, compared to when no breathing movements are observed. Mielke et al. report a case of S-shaped ductal kinking causing pulmonary regurgitation, right ventricular dilatation at 32 weeks and functional holosystolic tricuspid valve insufficiency. This resulted in cesarean delivery at 35 weeks. These findings are similar to the cardiac changes observed in ductal constriction, which makes these authors advise close monitoring and even termination of pregnancy. The issue of ductal shape and what degree of bending and dilatation is considered abnormal has been debated. Lindsay Allan argues that finding a dilated ductus arteriosus at the end of gestation is common and that it usually reverts spontaneously after birth. This suggests that it is the normal evolution of the ductus arteriosus.

Ductus arteriosus aneurysm (DAA) is characterized by a localized saccular or tubular dilation of the ductus arteriosus. It is a rare prenatal finding, first described by Puder et al. in 1995 at 39 weeks’ gestation. Although the incidence of neonatal ductus arteriosus aneurysm was previously reported to be 0.8%, based on neonatal autopsies, and 1.5-2.2% by fetal ultrasound studies at fetal age greater than 30-32 weeks, the incidence in full-term neonates is as high as 8.8%. Risk factors for a ductus arteriosus aneurysm include an inappropriately controlled maternal gestational diabetes together with large-for-gestational age fetuses, as well as the maternal blood group type A.

The underlying cause for this saccular protrusion and elongation of the ductus is still elusive. Several case series support the theory of wall weakness resulting from necrosis and mucoid degeneration of the media layer of the ductus. Other hypotheses suggest different possibilities: (1) an increase in blood flow via the ductus arteriosus with high velocities, (2) intrauterine constriction of the ductus close to the pulmonary end with post stenotic dilation, or (3) connective tissue disorders with abnormal intimal cushion formation or defective elastin. None of these theories can explain ductus arteriosus aneurysm formation in all patients.

The criteria for an antenatal diagnosis of ductus arteriosus aneurysm are the presence of a tortuous ductus arteriosus with a fusiform or saccular dilation that protrudes leftward of the aortic arch. The diameter of the dilated portion of the ductus arteriosus has to be more than the 95th percentile of the normal cross-sectional diameter for gestational age. Tseng and Jan differentiate ductus arteriosus aneurysm from ductus arteriosus dilatation (DAD), which is when a fusiform or saccular dilatation >95th percentile of the normal width of the ductus arteriosus is found in the absence of a tortuous ductus arteriosus. By color Doppler, there is a turbulent blood flow within the aneurysm. Tsai et al. describe late onset of large ductus arteriosus aneurysm in a fetus that presented with increased nuchal translucency and cystic hygroma at first trimester Down syndrome screening, but this finding should not be considered a marker of ductus arteriosus aneurysm.

The sonographic finding of a ductus arteriosus aneurysm is infrequently associated with additional abnormalities. However in a multi-institutional study, Dyamenahalli et al report fetuses with chromosomal defects (trisomy 21, trisomy 13, or Smith-Lemli-Opitz syndrome) and others with associated connective tissue disorders such as Marfan, Ehler-Danlos and Larson syndrome.

Although ductus arteriosus aneurysm can be associated with severe complications, the majority of affected fetuses are asymptomatic at birth since ductus arteriosus aneurysm usually resolves spontaneously following closure of the ductus arteriosus. The closure time was delayed in newborns with a ductus arteriosus aneurysm compared with that of the newborns without a ductus arteriosus aneurysm. The complications associated with ductus arteriosus aneurysm described in the postnatal period are spontaneous rupture, erosion, thromboembolism, infection, compression of adjacent structures, and even sudden death. Despite the fact that the complications associated with ductus arteriosus aneurysm usually occur postnatally, Sheridan et al have reported a rare case of a 2nd trimester fetus with extensive thrombosis and obstruction of the pulmonary artery and its branches secondary to a large post stricture ductus arteriosus aneurysm. This was complicated by pulmonary hypertension, right-sided heart failure and death.

Differential diagnosis may include pulmonary artery aneurysm, which is a rare cardiac malformation that can be congenital or acquired. Infections, Marfan syndrome, atherosclerosis, chronic pulmonary hypertension with or without congenital heart disease, and vasculitis can be associated with pulmonary artery aneurysms. Another congenital heart defect that must be differentiated from a ductus arteriosus aneurysm is absent pulmonary valve syndrome, which presents with severe dilatation of the pulmonary arteries (main, right, and left pulmonary arteries). However, this pathology is usually associated with an absent ductus arteriosus.

Suggested readings:
• Acherman RJ, Evans WN, Roberts D, et al. An unusual fetal ductus arteriosus pathway. J Ultrasound Med. 2008;27(7):1123-1124. doi:10.7863/jum.2008.27.7.1123
• Benson CB, Brown DL, Doubilet PM, et al. Increasing curvature of the normal fetal ductus arteriosus with advancing gestational age. Ultrasound Obstet Gynecol. 1995;5(2):95-97. doi:10.1046/j.1469-0705.1995.05020095.x
• Brezinka C. Fetal ductus arteriosus--how far may it bend?. Ultrasound Obstet Gynecol. 1995;6(1):6-7. doi:10.1046/j.1469-0705.1995.06010004-2.x
• Brown DL, Benson CB. The S-shaped ductus arteriosus. Ultrasound Obstet Gynecol. 1995;6(5):372. doi:10.1046/j.1469-0705.1995.06050372.x
• Dyamenahalli U, Smallhorn JF, Geva T, et al. Isolated ductus arteriosus aneurysm in the fetus and infant: a multi-institutional experience. J Am Coll Cardiol. 2000;36(1):262-269. doi:10.1016/s0735-1097(00)00707-5
• Ganesan S, Hutchinson DP, Sampson AJ. Prenatal diagnosis of ductus arteriosus aneurysm. Ultrasound. 2015;23(4):251-253. doi:10.1177/1742271X15587931
• Jackson CM, Sandor GG, Lim K, et al. Diagnosis of fetal ductus arteriosus aneurysm: importance of the three-vessel view. Ultrasound Obstet Gynecol. 2005;26(1):57-62. doi:10.1002/uog.1927
• Jan SL, Hwang B, Fu YC, et al. Isolated neonatal ductus arteriosus aneurysm. J Am Coll Cardiol. 2002;39(2):342-347. doi:10.1016/s0735-1097(01)01736-3
• Mielke G, Peukert U, Krapp M, et al. Fetal and transient neonatal right heart dilatation with severe tricuspid valve insufficiency in association with abnormally S-shaped kinking of the ductus arteriosus. Ultrasound Obstet Gynecol. 1995;5(5):338-341. doi:10.1046/j.1469-0705.1995.05050338.x
• Oh SJ, Jeung IC. A case of isolated congenital ductus arteriosus aneurysm detected by fetal echocardiography at 38 weeks of gestation. J Clin Ultrasound. 2011;39(9):530-533. doi:10.1002/jcu.20840
• Puder KS, Sherer DM, Ross RD, et al. Prenatal ultrasonographic diagnosis of ductus arteriosus aneurysm with spontaneous neonatal closure. Ultrasound Obstet Gynecol. 1995;5(5):342-345. doi:10.1046/j.1469-0705.1995.05050342.x
• Sheridan RM, Michelfelder EC, Choe KA, et al. Ductus arteriosus aneurysm with massive thrombosis of pulmonary artery and fetal hydrops. Pediatr Dev Pathol. 2012;15(1):79-85. doi:10.2350/11-02-0991-CR.1
• Tsai HD, Chen K, Lee ML, et al. Late onset of large benign ductus arteriosus aneurysm presented with increased nuchal translucency and cystic hygroma at first trimester Down syndrome screening. Taiwan J Obstet Gynecol. 2016;55(3):427-429. doi:10.1016/j.tjog.2016.04.020
• Tseng JJ, Jan SL. Fetal echocardiographic diagnosis of isolated ductus arteriosus aneurysm: a longitudinal study from 32 weeks of gestation to term. Ultrasound Obstet Gynecol. 2005;26(1):50-56. doi:10.1002/uog.1859
• Weichert J, Hartge DR, Axt-Fliedner R. The fetal ductus arteriosus and its abnormalities--a review. Congenit Heart Dis. 2010;5(5):398-408. doi:10.1111/j.1747-0803.2010.00424.x

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