Introduction:
- IVC thrombosis is an under recognized entity. It’s frequency in patients with deep venous thrombosis is 4-15%.
- A group of etiologies of IVC thrombosis is common to the general mechanics of deep venous thrombosis. However, there are some particular factors in this entity.
- The main causes of IVC thrombosis can be found in Table 1. They are distributed by their tumoral or non tumoral origin and by their underlying responsible mechanism of thrombus formation. Sometimes, more than one mechanism may contribute to the thrombus formation, like for example pregnancy, which is a hypercoagulable state and may also be responsible for extrinsic compression of the IVC.
Clinical manifestations
Ø Several clinical presentations may occur in IVC thrombosis once the IVC is a central vein without valves, collecting tributaries from the lower extremities and the abdomen. Patients may be asymptomatic or might have the classical inferior vena cava syndrome (bilateral lower extremity pain and swelling; visible superficial abdominal veins). Impaired renal function and Budd-Chiari syndrome may also occur depending on the obstruction level. Pulmonary embolism may also be the first sign of IVC thrombosis.
Diagnosis
Ø The diagnosis of IVC thrombosis depends on the demonstration of a true filling defect. In a non-contrast CT, a fresh thrombus has similar or higher density than the circulating blood and an old thrombus is of lower density. After contrast administration, the thrombus will appear as a low-density filling defect, surrounded by contrasted blood. In acute thrombosis, the IVC may appear larger than normal, opposing to chronic occlusion that may be atrophic and calcified.
Ø In MRI spin-echo images, the thrombus signal may be low or high and it stands out from the signal void of flowing blood. In gradient echo sequence, the opposite occurs. The thrombus appears like an area of lower signal against the bright flowing blood. A homogeneous thrombus favors an acute event, while a heterogeneous appearance with hypointense dots is seen in non-acute thrombus.
Ø Color Doppler sonography is an important tool once it is the exam most times performed to detect deep venous thrombosis, which can be associated with IVC thrombosis. The intra-hepatic IVC part is the most routinely examined, as it’s the most accessible to ultrasound examination. The rest of the IVC may be difficult to evaluate, depending on the quantity of intestinal gas or the patient’s body habitus. IVC thrombosis is usually detected by filling defects in the vessel lumen with an augmented IVC diameter and loss of the normal respiratory cycle of the vein.
Tumoral or nontumoral thrombus:
ØTrying to identify the nature of the thrombus may be challenging. However, this is an important point, as it will certainly influence the management of these patients. Tumoral thrombus may also have concomitant nontumoral thrombus, making their distinction more difficult.
- Significant expansion of the vein is usually indicative of tumoral thrombus.
- Color Doppler ultrasound and CT (arterial phase) documentation of vessels in the thrombus allows it’s differentiation in tumoral thrombus. CT heterogeneous enhancement with contrast material also indicates neovascularity.
Ø MRI findings that may help distinguish them are:
- High signal intensity on the first and second echo images, usually corresponding to a bland thrombus. Intermediate sign intensity can be seen in both types.
- Enhancement after gadolinium administration, which favors tumoral etiology as well as the same signal intensity as the primary tumor.
Ø The preoperative radiological study (MDCT or MRI) of tumoral IVC thrombosis should provide essential information:
- Identification of the primary tumor and eventual metastases;
- Precise information of the tumoral extension, including the superior limit and heart involvement (sagittal and coronal views are very useful for this purpose);
- Assessment of IVC wall invasion, which mandates a segmental IVC recession in addition to thrombectomy, is difficult to diagnose – the axial plan is the most helpful view to detect it. Identification of arterial recruitment from adjacent organs, like from the liver, may also be indicative of venous wall invasion;
- Detection of tumoral retroperitoneal extension;
- Identification of complications like pulmonary embolism or Budd-Chiari syndrome.
Collateral pathways:
- When the IVC is obstructed, there are several alternative pathways for the blood return to the heart. The prominent calibre of certain veins should call attention to the patency of the IVC. The most frequent collateral pathway is made from the connection of the ascending lumbar veins with the azygos (on the right) and hemiazygos (on the left) veins. Flow may also be directed through the intravertebral, paraspinal and extravertebral plexus (Batson plexus).
Diagnostic Modalities:
Advantages and disadvantages
Ø With the current availability of the MDCT scanners that allow multiplanar reformations (MPR) and volume rendering technique (VRT), this modality has been gaining territory to others techniques (MRI and color Doppler sonography) to evaluate IVC pathology.
Ø Advantages of MDCT include superior spatial resolution and fast image acquisition. CT is the best option when concomitant pulmonary embolization is suspected.
Ø CT is the most common method used in staging abdominal tumors that may spread to the IVC, which sometimes may be an incidental finding. However, unless IVC disease is suspected or an IVC study is requested, an additional late phase is usually required, increasing the amount of ionizing radiation exposition.
Ø MRI is useful in ambiguous CT findings and in patients that cannot receive iodinated contrast material. MRI has better tissue contrast resolution and can detect IVC thrombus even without intravenous contrast administration.