Case of the Week #537

Javier Cortejoso; Julio Díaz; María López-Menéndez; Fernando Centeno

Answer

This case demonstrates isolated interruption of the inferior vena cava.

The ultrasound examination in axial thorax sections at the level of the four-chamber view shows the finding of two vessels ("double vessel” sign) of similar size in a paraspinous location posterior to the heart (Image 1). This finding is also visible in the abdomen (Image 2). Coronal views confirmed two parallel vessels in a paraspinal location and the inferior vena cava could not be identified in a parasagittal section (Image 3). The hepatic veins drained directly into the right atrium or to a short inferior vena cava. At the level of the three-vessel and trachea view, the azygos vein is visible coursing anteriorly to join the superior vena cava (Image 4). Using color Doppler, the vessel located posterior and to the right of the aorta is identified as the azygos vein, with flow in the ascending direction, and empties at the level of the superior vena cava (Image 5, 6). The echocardiographic examination was completely normal (Video 1, 2).

At 38+6 weeks’ gestation, an apparently normal and healthy 2950 g girl was born after an uncomplicated spontaneous delivery. The echocardiographic study of the newborn confirmed the diagnosis. The infant thus far is developing normally.

Image 1 labels — Image 1: Abnormal four-chamber view displaying two vessels (aorta and azygos vein) running behind the heart

Image 2 copyright label — Image 2: Transverse view of the fetal abdomen with the “double vessel” sign

Image 3 copyright label — Image 3: Parallel aorta and azygos in a thoraco-abdominal coronal section

Image 4 copyright label — Image 4: Dilated azygos vein in the three-vessel and trachea view

Image 5 copyright — Image 5: Descending aorta (blue) and ascending azygos vein (red) in the sagittal section of the thorax

Image 6 copyright — Image 6: Drainage from the left hepatic vein (LHV) and the hepatic segment of the IVC to the right atrium (PulmV: pulmonary vein)

Image 7 copyright — Image 7: Arrival of the azygos vein to the superior vena cava (aorta blue, azygos red)

Discussion

Interruption of the inferior vena cava (IVC) is defined as the absence of the IVC between the renal and hepatic portions [1]. Drainage to the heart will be done through its collaterals, usually through the azygos vein to the right superior vena cava, although very rarely it can also be done through the hemiazygos vein [1] . Drainage of the suprahepatic veins will be performed in both cases directly to the right atrium.

The first prenatal diagnosis of interrupted inferior vena cava was made in 1999 by Celentano [2]. The incidence as an isolated finding is 1 in 5000 pregnancies [3], which is less than postnatal prevalence of 0.6% [4]. It is considered a prenatal ultrasound marker of isomerisms and/or heart disease [5]; therefore, its finding requires careful ultrasound examination of the fetal heart with determination of visceral situs. The diagnosis in isolated cases is often made incidentally in adulthood. It likely has more clinical implications in adulthood due to its association with deep venous thrombosis [6]. Additionally, the diagnosis of interrupted inferior vena cava is important to avoid possible surgical or venous catheterization complications.

The infrahepatic IVC develops as a composite structure formed from a complex process that includes formation, regression, and midline anastomosis of the three longitudinal pairs of veins: postcardinal, subcardinal, and supracardinal [7]. It is formed between 6 and 8 weeks of gestation from the hepatic vein, right subcardinal vein, supra-subcardinal anastomosis, and right supracardinal vein [8]. Each of these embryonic veins will respectively originate a segment of the final structure of the IVC: hepatic, suprarenal, renal, and infrarenal.

Video 3: Normal development of the Inferior Vena Cava from the Posterior Cardinal, Subcardinal and Supracardinal veins. Also viewable at this link: https://youtu.be/f8d2qXrDhwE

During this complex transformation of the IVC, numerous variations and anomalies to its adult form may occur. The most frequent is azygos continuation of the IVC, which has also been termed absence of the hepatic segment of the IVC with azygos continuation [4]. Failure to form the right subcardinal-hepatic anastomosis (with resulting atrophy of the right subcardinal vein) determines that the anastomosis between the subcardinal and right supracardinal veins collects the blood from the lower body, diverting it to the cranial end of the right supracardinal vein (azygos vein). This passes posterior to the diaphragmatic crura to enter the thorax and joins the superior vena cava at the normal location in the right paratracheal space [7,8]. The hepatic segment is ordinarily not truly absent; rather, it drains directly into the right atrium.

Under normal conditions, the only major vessel that can be observed behind the heart is the descending aorta, which is positioned on the left side of the spine and on the same side as the cardiac apex. The finding of two vessels running behind the heart in the four-chamber view is usually pathological and may be caused by interrupted IVC with azygos continuation (excellent marker of left isomerism) or by total anomalous pulmonary venous connection (typical of right isomerism) [9]. In the first case, the aorta and azygos vein are located in close proximity on the same side of the spine (“double vessel” sign), whereas in the second, the pulmonary venous confluence is situated immediately behind the atrium and a wide gap is apparent between the posterior wall of the atrium and the descending aorta.

Interruption of the IVC with azygos continuation is diagnosed by imaging two vessels (“double vessel” sign) of similar size in a paraspinous location posterior to the heart [5]. This sign is easily detected in transverse views of the thorax and abdomen, and can be confirmed on longitudinal views. Compared to the normal relationship, which shows only the aorta posterior to the heart, interruption of the IVC results in collateral flow through the azygos vein, which becomes enlarged and readily visible. This should be distinguished from the normal azygos vein, which occasionally can be visualized in the third trimester as a small 1 to 2 mm structure.

The “double vessel” sign has been described in a high percentage (80 to 96%) of left isomerism [9,10,11], but it can also be found in few cases of right isomerism [12] and as a benign vascular malformation with situs solitus and without congenital heart disease [1,2,3,9,13]. In combination with cardiac anomalies or situs abnormalities, interruption of the IVC with azygos continuation should suggest a specific diagnosis of heterotaxy, especially left isomerism. In addition, a strong association between large omphaloceles and interruption of the IVC with azygos continuation has also been documented prenatally [14].

In any case of diagnosis of an interruption of the IVC, a thorough fetal search for associated anomalies is indicated, with a special emphasis on possible cardiac abnormalities and heterotaxy. It is convenient to inform parents of the good prognosis if it is an isolated finding, although it is important to inform them of possible complications associated with invasive procedures and of the increased risk of deep-vein thrombosis.

References

[1] Savirón Cornudella R, Pérez Pérez P, De Diego Allué E, et al. Interrupción de vena cava inferior. Diagnóstico prenatal de sus variantes. Rev chil obstet ginecol. 2017;82(6):626-632.
[2] Celentano C, Malinger G, Rotmensch S, et al. Prenatal diagnosis of interrupted as an isolated finding: a benign vascular malformation. Ultrasound Obstet Gynecol. 1999;14(3):215‐218.
[3] Bronshtein M, Khatib N, Blumenfeld Z. Prenatal diagnosis and outcome of isolated interrupted inferior vena cava. Am J Obstet Gynecol. 2010;202(4):398.e1‐398.e3984.
[4] Ginaldi S, Chuang VP, Wallace S. Absence of hepatic segment of the inferior vena cava with azygous continuation. J Comput Assist Tomogr. 1980;4(1):112‐114.
[5] Sheley RC, Nyberg DA, Kapur R. Azygous continuation of the interrupted inferior vena cava: a clue to prenatal diagnosis of the cardiosplenic syndromes. J Ultrasound Med. 1995;14(5):381‐387.
[6] Ruggeri M, Tosetto A, Castaman G, et al. Congenital absence of the inferior vena cava: a rare risk factor for idiopathic deep-vein thrombosis. Lancet. 2001;357(9254):441.
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[10] Thakur V, Jaeggi ET, Yoo SJ. "Abnormal visceral and atrial situs and congenital heart disease." Fetal Cardiology: Embryology, Genetics, Physiology, Echocardiographic Evaluation, Diagnosis and Perinatal Management of Cardiac Diseases, 3rd edition. Boca Raton, FL: CRC Press, 2019: pgs 239-252.
[11] Berg C, Geipel A, Kamil D, et al. The syndrome of left isomerism: sonographic findings and outcome in prenatally diagnosed cases. J Ultrasound Med. 2005;24(7):921‐931.
[12] Ruscazio M, Van Praagh S, Marrass AR, et al. Interrupted inferior vena cava in asplenia syndrome and a review of the hereditary patterns of visceral situs abnormalities. Am J Cardiol. 1998;81(1):111‐116.
[13] Giang do TC, Rajeesh G, Vaidyanathan B. Prenatal diagnosis of isolated interrupted inferior vena cava with azygos continuation to superior vena cava. Ann Pediatr Cardiol. 2014;7(1):49‐51.
[14] Mlczoch E, Carvalho JS. Interrupted inferior vena cava in fetuses with omphalocele. Case series of fetuses referred for fetal echocardiography and review of the literature. Early Hum Dev. 2015;91(1):1‐6.