Symptoms are usually relieved with radiation therapy within one month of treatment. However, even with treatment, 99% of patients die within two and a half years. This relates to the cancerous causes of SVC that are 90% of the cases. The average age of onset of disease is 54 years of age.

Approximately 90% of cases are associated with a cancerous tumor that is compressing the superior vena cava, such as bronchogenic carcinoma including small cell and non-small cell lung carcinoma, Burkitt's lymphoma, lymphoblastic lymphomas, pre-T-cell lineage acute lymphoblastic leukemia (rare), and other acute leukemias. Syphilis and tuberculosis have also been known to cause superior vena cava syndrome. SVCS can be caused by invasion or compression by a pathological process or by thrombosis in the vein itself, although this latter is less common (approximately 35% due to the use of intravascular devices).

Epidemiological data is elusive owing to the wide variety of clinical presentation. In the U.S., incidence is estimated to be at 5–10 cases per 100,000 per year. Minor compression of the inferior vena cava during pregnancy is a relatively common occurrence. It is seen most prevalently when women lie on their back or right side. 90% of women lying in the supine position during pregnancy experience inferior vena cava syndrome; however, not all of the women display symptoms.

Inferior vena cava syndrome (IVCS) is a result of obstruction of the inferior vena cava. It can be caused by invasion or compression by a pathological process or by thrombosis in the vein itself. It can also occur during pregnancy.Pregnancy can lead to problems with blood return due to high venous pressure in the lower limbs, failure of blood return to the heart, decreased cardiac output due to obstructions in inferior vena cava, sudden rise in venous pressure which can lead to placental separation, and a decrease in renal function. All of these issues can arise from lying in the supine position during late pregnancy which can cause compression of the inferior vena cava. Symptoms of late pregnancy inferior vena cava syndrome consist of intense pain in the right hand side, muscle twitching, drop of blood pressure, and fluid retention.

For individuals who survive the initial crush injury, survival rates are high for traumatic asphyxia.

Congenital stenosis of vena cava is a congenital anomaly in which the superior vena cava or inferior vena cava has an aberrant interruption or coarctation.

In some cases, it can be asymptomatic, and in other cases it can lead to fluid accumulation and cardiopulmonary collapse.

In PLSVC, the left brachiocephalic vein does not develop fully and the left upper limb and head & neck drain into the right atrium via the coronary sinus.

The variation, in isolation, is considered benign, but is very frequently associated with cardiac abnormalities (e.g. ventricular septal defect, atrioventricular septal defect) that have a significant mortality and morbidity. It is more frequent in patients with congenital heart defects.

The sudden impact on the thorax causes an increase in intrathoracic pressure. In order for traumatic asphyxia to occur, a Valsalva maneuver is required when the traumatic force is applied. Exhalation against the closed glottis along with the traumatic event causes air that cannot escape from the thoracic cavity. Instead, the air causes increased venous back-pressure, which is transferred back to through the right atrium, to the superior vena cava and to the head and neck veins and capillaries.

Scimitar syndrome, or congenital pulmonary venolobar syndrome, is a rare congenital heart defect characterized by anomalous venous return from the right lung (to the systemic venous drainage, rather than directly to the left atrium). This anomalous pulmonary venous return can be either partial (PAPVR) or total (TAPVR). The syndrome associated with PAPVR is more commonly known as "Scimitar syndrome" after the curvilinear pattern created on a chest radiograph by the pulmonary veins that drain to the inferior vena cava. This radiographic density often has the shape of a scimitar, a type of curved sword. The syndrome was first described by Catherine Neill in 1960.

CTEPH is an orphan disease with an estimated incidence of 5 cases per million, but it is likely that CTEPH is under-diagnosed as symptoms are non-specific. Although a cumulative incidence of CTEPH between 0.1% and 9.1% within the first 2 years after a symptomatic PE has been reported, it is currently unclear whether acute symptomatic PE begets CTEPH. Routine screening for CTEPH after PE is not recommended because a significant number of CTEPH cases develops in the absence of previous acute symptomatic PE. In addition, approximately 25% of patients with CTEPH do not present with a clinical history of acute PE. The median age of patients at diagnosis is 63 years (there is a wide age range, but paediatric cases are rare), and both genders are equally affected.

In anatomy, a persistent left superior vena cava (PLSVC) is the most common variation of the thoracic venous system, is prevalent in 0.3% of the population, and an embryologic remnant that results from a failure to involute.

Historically the prognosis for patients with untreated CTEPH was poor, with a 5-year survival of 40 mmHg at presentation. More contemporary data from the European CTEPH registry have demonstrated a 70% 3-year survival in patients with CTEPH who do not undergo the surgical procedure of pulmonary endarterectomy (PEA). Recent data from an international CTEPH registry demonstrate that mortality in CTEPH is associated with New York Heart Association (NYHA) functional class IV, increased right atrial pressure, and a history of cancer. Furthermore, comorbidities such as coronary disease, left heart failure, and chronic obstructive pulmonary disease (COPD) are risk factors for mortality.

Anomalous pulmonary venous connection (or anomalous pulmonary venous drainage or anomalous pulmonary venous return) is a congenital defect of the pulmonary veins.

In TAPVC without obstruction, surgical redirection can be performed within the first month of life. The operation is performed under general anesthesia. The four pulmonary veins are reconnected to the left atrium, and any associated heart defects such as atrial septal defect, ventricular septal defect, patent foramen ovale, and/or patent ductus arteriosus are surgically closed. With obstruction, surgery should be undertaken emergently. PGE1 should be given because a patent ductus arteriosus allows oxygenated blood to go from the circulation of the right heart to the systemic circulation.

The mediastinum (from Medieval Latin "mediastinus", "midway") is the central compartment of the thoracic cavity surrounded by loose connective tissue, as an undelineated region that contains a group of structures within the thorax. The mediastinum contains the heart and its vessels, the esophagus, trachea, phrenic and cardiac nerves, the thoracic duct, thymus and lymph nodes of the central chest.

Some recent research has suggested that a proportion of cases of migraine may be caused by PFO. While the exact mechanism remains unclear, closure of a PFO can reduce symptoms in certain cases. This remains controversial; 20% of the general population has a PFO, which for the most part, is asymptomatic. About 20% of the female population has migraines, and the placebo effect in migraine typically averages around 40%. The high frequency of these facts finding statistically significant relationships between PFO and migraine difficult (i.e., the relationship may just be chance or coincidence). In a large randomized controlled trial, the higher prevalence of PFO in migraine patients was confirmed, but migraine headache cessation was not more prevalent in the group of migraine patients who underwent closure of their PFOs.

Surgical correction should be considered in the presence of significant left to right shunting (Qp:Qs ≥ 2:1) and pulmonary hypertension. This involves creation of an inter-atrial baffle to redirect the pulmonary venous return into the left atrium. Alternatively, the anomalous vein can be re-implanted directly into the left atrium.

Presence of a cystic hygroma increases the risk of HLHS in a fetus.

In a retrospective analysis of over 1,300 newborns (born between 1996 and 2006) from 24 children’s hospitals in the United States, researchers at Cincinnati Children’s Hospital in Ohio found that babies with HLHS were more likely to be born in summer months, suggesting that seasonality and environmental factors may play a significant role in causation.

Cardiac:

- constrictive pericarditis. One study found that pulsus paradoxus occurs in less than 20% of patients with constrictive pericarditis.

- pericardial effusion, including cardiac tamponade

- cardiogenic shock

Pulmonary:

- pulmonary embolism

- tension pneumothorax

- asthma (especially with severe asthma exacerbations)

- chronic obstructive pulmonary disease

Non-pulmonary and non-cardiac:

- anaphylactic shock

- hypovolemia

- superior vena cava obstruction

- pregnancy

- obesity

PP has been shown to be predictive of the severity of cardiac tamponade. Pulsus paradoxus may not be seen with cardiac tamponade if an atrial septal defect or significant aortic regurgitation is also present.

Treatment depends on the severity and symptoms. Treatments include:

- Endovascular stenting.

- Renal vein re-implantation.

- Gonadal vein embolization.

The intrahepatic shunts found in large dog breeds are passed on in a simple autosomal recessive way, while the extrahepatic shunts of the small breeds are inherited on a polygenic basis.

Vein of Galen malformations are devastating complications. Studies have shown that 77% of untreated cases result in mortality. Even after surgical treatment, the mortality rate remains as high as 39.4%. Most cases occur during infancy when the mortality rates are at their highest. Vein of Galen malformations are a relatively unknown affliction, attributed to the rareness of the malformations. Therefore, when a child is diagnosed with a faulty Great Cerebral Vein of Galen, most parents know little to nothing about what they are dealing with. To counteract this, support sites have been created which offer information, advice, and a community of support to the afflicted (, ).

The nutcracker syndrome (NCS) results most commonly from the compression of the left renal vein between the abdominal aorta (AA) and superior mesenteric artery (SMA), although other variants exist. The name derives from the fact that, in the sagittal plane and/or transverse plane, the SMA and AA (with some imagination) appear to be a nutcracker crushing a nut (the renal vein).

There is a wide spectrum of clinical presentations and diagnostic criteria are not well defined, which frequently results in delayed or incorrect diagnosis.

This condition is not to be confused with superior mesenteric artery syndrome, which is the compression of the third portion of the duodenum by the SMA and the AA.

Although its cause is poorly understood, situs ambiguous has been linked to family history of malformations and maternal cocaine use, suggesting both genetic and environmental factors play a role. Several genes in the TGF-beta pathway, which controls left-right patterning of viseral organs across the body axis, have been indicated in sporadic and familial cases of atrial isomerism.

There does not appear to be a screening method for prevention of heterotaxy syndrome. However, genetic testing in family members that display atrial isomerism or other cardiac malformations may help to discern risk for additional family members, especially in X-linked causes of heterotaxy syndrome.