Normal Development or Embryogenesis 

• At 4 weeks of life, 3 distinct venous systems form: the vitelline system drains the gut, the umbilical system drains the placenta, and the cardinal system drains the rest of the embryo. The cardinal veins are divided into anterior and posterior cardinal veins, joining to form the common cardinal veins, which drain into the sinus venosus.

 The superior vena cava is formed from the right anterior and the right common cardinal veins.

 The inferior vena cava develops through a complex pattern of venous development, anastomosis, and regression of three pairs of veins: the supracardinal, subcardinal, posterior cardinal veins and the vitelline veins(1). 

Fig. 1: Schematic representation of the embryologic development of the inferior vena cava.
References: Department of Radiology and Medical Imaging, University Emergency Hospital of Bucharest, Romania

Fig. 2: Embryological origin of the inferior vena cava.
References: Department of Radiology and Medical Imaging, University Emergency Hospital of Bucharest, Romania

Superior vena cava congenital anomalies

· Persistent left superior vena cava (PLSVC) is the most common congenital venous anomaly in the chest. The vast majority of cases are accompanied by a normal right-sided SVC, termed SVC duplication.

Fig. 3: Drawing ilustrates double SVC due to persistent left superior vena cava.
References: Department of Radiology and Medical Imaging, University Emergency Hospital of Bucharest, Romania

 This anomaly is caused by persistence of the left anterior cardinal vein and its continuity with the left common cardinal vein. Drainage is usually into the coronary sinus and then into the right atrium with no clinical consequences (2). In 10% of patients it attaches to the left atrium, causing right-to-left shunting, which can determine hemodynamic compromise (3). 

 Appears on CT as an ovoid structure that may show very little enhancement or may enhance intensely, depending on the site of the contrast injection and the phase of the scan. The anomalous vessel is coursing inferiorly to the left of the arch of the aorta and anterior to the main trunk of the left pulmonary artery. It is in direct continuation of the confluence of the left jugular and the left subclavian vein. Confusion with lymph nodes is avoided by tracing the course of the vessel.

Fig. 4: Double SVC. Chest CT axial sections (a,b) show SVC duplication due to the presence of a persistent left SVC accompanied by a normal right-sided SVC and sagittal reconstruction (c) demonstrates drainage of left SVC into the coronary sinus and then into the right atrium.
References: Department of Radiology and Medical Imaging, University Emergency Hospital of Bucharest, Romania

Fig. 5: Partial anomalous pulmonary venous connection in the same patient. Sagittal (a) and axial (b) maximum intensity projection (MIP) and 3D CT reconstruction (c) images showing the right superior pulmonary vein draining into the right SVC. The right middle pulmonary vein drainage is seen both into the right SVC and into the right atrium, thus creating a communication between right SVC, right atrium and left atrium.
References: Department of Radiology and Medical Imaging, University Emergency Hospital of Bucharest, Romania

In most cases, this abnormality is clinically silent and may be discovered incidentally during CT scanning of the chest. However this situation may cause difficulties and potential complications in case the subject undergoes CVC placement, angiography, or cardiothoracic surgery.

Inferior vena cava congenital anomalies

Variants usually involve the infrarenal segment. There is a multitude of venous variants in the abdomen that can be distinguished by following the inferior vena cava (or its substitute) upward towards the heart and downward into the pelvis.

 · post-renal segment

Fig. 6: Schematic representation of congenital anomalies of the post-renal segment of IVC.
References: Department of Radiology and Medical Imaging, University Emergency Hospital of Bucharest, Romania

 1. Transposition of IVC or left-sided IVC

The left IVC joins the left renal vein and crosses anterior to the aorta in the normal fashion to join the normal (right-sided) IVC. Left IVC can be misdiagnosed as a left-sided para-aortic lymphadenopathy. A left IVC may make transjugular access to the infrarenal IVC for caval filter placement difficult (4).

 2. Duplication of IVC

There are bilateral IVCs wich ascend on each side of the aorta. The left IVC ends at the level of the left renal vein, crossing over to join the right IVC. Duplication of the IVC should be suspected in cases of recurrent pulmonary embolism after placement of an IVC filter, despite adequate anticoagulation.

 3. Retrocaval or circumcaval ureter

The proximal ureter becomes trapped posterior and medial to the IVC. This can cause significant ureteral compression, leading to hydronephrosis or recurrent urinary tract infections. On imaging, retrocaval ureter appears like a fish hook or a reverse J, with the proximal ureter appearing at the level of the lumbar pedicles (5). Occurs almost always on the right side.

4. Absent infrarenal inferior vena cava

It is a rare anomaly which can be either complete or incomplete depending on the degree of involvement of the infrarenal IVC and the common iliac veins. The venous collaterals that develop can simulate a mediastinal mass.

Fig. 7: Axial section at the level of infra renal aorta (a) and volume rendering reconstruction in the venous phase (b) shows no visualization of IVC with multiple tortuous vascular channels seen in the para aortic region (more prominent left endopelvic). Few of these channels show nonocclusive thrombus within (c- white arrows).
References: Department of Radiology and Medical Imaging, University Emergency Hospital of Bucharest, Romania

 · renal segment 

Fig. 8: Schematic representation of congenital anomalies of the renal segment of IVC
References: Department of Radiology and Medical Imaging, University Emergency Hospital of Bucharest, Romania

 1. Circumaortic venous collar

 There are 2 left renal veins, with one vein coursing anterior and the other posterior to the aorta. Care should be taken to avoid misdiagnosis of this condition as retroperitoneal adenopathy (6). Compression of the renal vein by the aorta can cause hematuria, abdominal/flank pain or “nutcracker” phenomenon, which entails hypertension, hematuria, and ureteric varices (7).

 2. Retroaortic left renal vein 

It can be isolated or be combined with a normal left renal vein,or with variants of the IVC. Many retroaortic left renal veins take a downward course before crossing the aorta and entering the IVC. On non-contrast scans it should not be mistaken for a lymph node. Multiple or bifurcated renal veins are quite common and gain importance in living renal donors.

Fig. 9: Retroaortic left renal vein. Contrast-enhanced CT scan shows the left renal vein coursing between the aorta and the vertebra and draining into the IVC.
References: Department of Radiology and Medical Imaging, University Emergency Hospital of Bucharest, Romania

· renal segment 

Fig. 10: Schematic representation of Azygos continuation of IVC.
References: Department of Radiology and Medical Imaging, University Emergency Hospital of Bucharest, Romania

Azygos continuation of IVC is a rare syndrome based on the aplasia of one segment of the IVC. The infrarenal IVC continues as the azygos vein and, in cases of left IVC, as the hemiazygos vein. The renal segment of the IVC receives venous return from both kidneys and passes posterior to the diaphragmatic crura to enter the thorax as the azygos vein. The hepatic veins drain directly into the right atrium.  The abdominal and especially the thoracic portions of the azygos and hemiazygos veins are markedly dilated and in some cases may exceed the aortic diameter. The anomaly can mimic esophageal varices.

 As a rule, anatomic variants of the venous system are an incidental finding. An awareness of these variants is crucially important for cardiopulmonary surgeries and because they can be misdiagnosed as a mass lesion. CT provides definitive clarification. IVC anomalies are recognized as a possible risk factor for deep vein thrombosis (DVT), especially in young adults.

Thrombosis

Fresh venous thrombi are hyperattenuating on noncontrast scans, and become hypoattenuating as they become older and organize. Following contrast administration they appear as filling defects that may occupy the center or periphery of the venous lumen. Collateral formation is an indicator of an older process.

It is important to differentiate bland thrombus from tumor thrombus.

Fig. 11: Abdominal CT scan showing central filling defect (consistent with thrombus) in the inferior vena cava.
References: Department of Radiology and Medical Imaging, University Emergency Hospital of Bucharest, Romania

Fig. 12: Hepatocellular carcinoma invading the inferior vena cava. Coronal computed tomography scan showing multiple ill-defined and partially confluent hypodensities of different size suggesting an advanced neoplastic process. The intrahepatic segment of the inferior vena cava becomes progressively compressed by the tumor.
References: Department of Radiology and Medical Imaging, University Emergency Hospital of Bucharest, Romania

Thrombophlebitis is characterized by the same criteria as venous thrombosis but is combined with edema and stranding in the surrounding tissue. 

Fig. 13: CT image shows parietal thrombi at the level of the IVC (a) with extension of thrombus into the superior mesenteric vein (b) and associated thrombophlebitis of the right femoral vein (c).
References: Department of Radiology and Medical Imaging, University Emergency Hospital of Bucharest, Romania

Pseudothrombosis

The incomplete mixing of opacified and nonopacified blood can mimic a filling defect, creating the appearance of an intraluminal thrombus. Persistent filling defect (clot) should be confirmed on later venous phases.

This problem can be avoided by a sufficient delay before initiating the spiral scan.

Fig. 14: Pseudothrombosis. Filling defect caused by inflow of opacified blood from the renal veins mixing with nonopacified blood coming into the IVC from the pelvis and lower limbs.
References: Department of Radiology and Medical Imaging, University Emergency Hospital of Bucharest, Romania

Trauma

The presence of a collapsed infrahepatic IVC may be an important CT sign of severe hypovolemia or hypotension, resulting from major blood loss in blunt trauma patients and may signify impending cardiovascular collapse.

Fig. 15: Computed tomography scan shows flattening of the inferior vena cava (b) due to hypovolemia in a trauma patient, associating a zone of low attenuation around the intrahepatic segment of the IVC (a).
References: Department of Radiology and Medical Imaging, University Emergency Hospital of Bucharest, Romania