Normal Anatomy and Congenital Anomalies

The IVC extends from the confluence of the common iliac veins at the level of L5 vertebral body, to the right atrium of the heart in right prevertebral location, next to the abdominal aorta and is surrounded by a rich network of lymphatic vessels (Fig. 110-1). It is partially covered anteriorly by the peritoneal membrane. The retroperitoneal space where the IVC is located can communicate with the perirenal spaces and the anterior and posterior interfascial spaces.¹

FIGURE 110-1 Normal IVC. A, Contrast-enhanced CT of the abdomen depicts axial images at the level of the renal veins showing normal location and size of the IVC located to the right of the aorta. This image, obtained at portal-venous phase at the level of the left renal vein, shows heterogeneous luminal enhancement due to mixing of the renal vein blood with the inferior IVC blood. B, Sagittal reformat of the same study shows IVC segments with different luminal enhancement due to the normally observed different timing of the contrast return. Therefore we recommend imaging with longer delays (2 to 4 minutes) in order to obtain more homogeneous luminal enhancement.

The shape of the IVC varies from round to ovoid or even flat depending on a multitude of factors such as intrathoracic pressure, blood volume status, or the presence of congestive heart failure. The IVC receives a number of tributaries including common iliac, lumbar, renal, right adrenal, and hepatic veins. The IVC lies between the liver and the diaphragm and cephalad courses medially to enter the right atrium. At this level, a fat pad (continuous with the retroperitoneal fat) can be seen in many normal patients in an inferomedial location, sometimes bulging into the lumen of the IVC. This fat should not be considered pathologic and should not generate any further work-up studies.

Congenital anomalies of the IVC generally include abnormal position of the IVC or absence of IVC. The most common IVC anomalies are: (1) left IVC, (2) duplicated IVC, (3) azygos continuation of IVC, (4) circumaortic left renal vein, (5) retroaortic left renal vein, (6) circumcaval or retrocaval ureter, (7) duplicated right renal vein, (8) absence of infrarenal or entire IVC, (9) duplicated IVC with retroaortic right renal vein and hemiazygos continuation of the IVC, and (10) duplication of IVC with retroaortic left renal vein and azygos continuation of the IVC.

Left IVC: The infrarenal IVC is located to the left of the abdominal aorta, then it joins the left renal vein which then crosses anterior to the abdominal aorta and along with the right renal vein forms the normal right-sided prerenal IVC.

Duplicated IVC: There are two IVCs below the level of the renal veins—each connected to the ipsilateral common iliac vein. The left IVC joins the left renal vein, which then crosses anterior to the abdominal aorta and drains into the right IVC (Fig. 110-2). There may be variants in this anatomy and there may be significant discrepancy in the size of the two IVCs.

FIGURE 110-2 IVC duplication (infrarenal). Contrast-enhanced CT shows two IVC—one on each side of the aorta. The left sided IVC originates in the left iliac vein and drains into the left renal vein (arrows) to join the right IVC (I) and form a single vein superior to the renal vessels.

Azygos continuation of IVC: The infrarenal portion of IVC receives blood from the renal veins. It passes posterior to the diaphragmatic crura, enters the thorax as the azygos vein, and then joins the superior vena cava at the azygos arch. The hepatic and right adrenal veins drain directly into the right atrium. The gonadal veins drain into the ipsilateral renal veins. The right renal artery crosses abnormally anterior to the IVC (Fig. 110-3).

FIGURE 110-3 Azygos-hemiazygos continuation of the IVC with duplication of the infrarenal IVC. A, Contrast-enhanced CT axial images show infrarenal IVC (I) and a smaller duplicated left IVC (arrow) that arises from the left iliac vein. B, CECT at a higher level demonstrates the absence of the intrahepatic portion of the IVC, which continues through the azygos vein (A) in retrocrural location. The image also shows a large hemiazygos vein (arrow) that arises from the left renal vein as continuation of the left IVC. C, Thick coronal MIP reformat shows the duplicated infrarenal IVC with the left (arrow) draining into the left renal vein and crossing behind the aorta (black arrow). The right IVC (I) continues through the azygos vein (A) above the level of the renal veins. D, Sagittal MIP reformat shows the azygos (A) continuation of the right IVC and how it connects to the SVC (S) through the azygos arch. Note the absence of the intrahepatic IVC and how the hepatic veins drain directly into the right atrium (arrow).

Circumaortic left renal vein: There are two left renal veins. The superior-anterior renal vein receives the adrenal vein and crosses the aorta anteriorly to join the IVC. The second renal vein is approximately 1 to 2 cm more inferior and posterior. It receives the left gonadal vein and crosses posterior to the aorta to join the IVC (Fig. 110-4).

FIGURE 110-4 Circumaortic left renal vein. A, CECT of the abdomen shows a left renal vein crossing anterior to the aorta (arrow). The origin of a second, posterior left renal vein is visualized (arrowhead). B, CECT of the abdomen shows the posterior left renal vein (arrow) crossing behind the abdominal aorta 1 cm caudad to the anterior left renal vein. C, Axial oblique MIP shows both renal veins (R) surrounding the aorta.

Retroaortic left renal vein: The renal vein crosses posterior to the aorta to join the IVC.

Circumcaval ureter (also known as retrocaval ureter): The anomaly always occurs on the right side. The proximal right ureter courses posterior to the IVC, emerges to the right of the aorta, and lies anterior to the right iliac vessel.

Duplicated right renal vein: There is presence of two right renal veins, one anterior and one posterior, usually at the same level.

Partial or complete absence of IVC: The variants of this anomaly include complete absence of the entire IVC which may include the iliac veins as well and partial absence of IVC with preservation of the suprarenal segment. In either case, the iliac veins join to form enlarged ascending lumbar veins. If the entire IVC is absent, the anterior paravertebral collateral vessels convey the blood return to the azygos and hemiazygos veins. If the suprarenal IVC is present, it receives blood from the renal veins. With partial or complete absence of the IVC, large gonadal and parauterine veins can be seen.

Duplication of IVC with retroaortic right renal vein and hemiazygos continuation of the IVC: There are two IVCs below the level of the renal veins. The right IVC joins the right renal vein, which crosses posterior to the aorta to drain in the left IVC. The left IVC then passes posterior to the diaphragmatic crura and continues into the thorax as the hemiazygos vein. There may be a significant size difference between the two vessels. In the thorax, the hemiazygos vein may have any of these different drainage pathways: (1) it crosses posterior to the aorta at about T8 to T9 to join the rudimentary azygos vein; (2) it joins a persistent left SVC and drains into the coronary vein; (3) an accessory hemiazygos continues to join the left brachiocephalic vein.

Duplication of IVC with retroaortic left renal vein and azygos continuation of IVC: There are two infrarenal IVCs. The left IVC joins the left renal vein which then crosses posterior to the aorta to join the right IVC. It passes posterior to the diaphragmatic crura and enters the thorax as azygos vein. It then joins the superior vena cava at its normal location in the right paratracheal space. The hepatic segment may not be truly absent. It drains directly into the right atrium.

Embryogenesis

Knowledge of the IVC embryogenesis is necessary for a better understanding of the IVC anatomic aberrations. The IVC is composed of four segments which form during the 6 to 8 weeks postconception.^2,3 This is due to continuous appearance and regression of three paired embryonic veins, which include the posterior cardinal veins, the subcardinal veins, and the supracardinal veins. The first step in this complex process is the formation of the posterior supracardinal and more anterior subcardinal veins. Then, the most caudal segment of the right supracardinal vein becomes the infrarenal vena cava. The hepatic segment of IVC is derived from the vitelline vein, which conveys blood from the viscera. The suprarenal segment is formed via a subcardinal-hepatic anastomosis. The renal segment forms via anastomosis of the right supra-subcardinal and post-subcardinal veins. The infrarenal segment arises from the right supracardinal vein.

Congenital anomalies of IVC are due to interruption of normal regression or lack of development of the different segments. The circumaortic venous ring and retroaortic left renal vein are related to aberrant development of the renal segment. Azygos continuation of the IVC results when there is a developmental anomaly involving the suprarenal segment.

Early in embryogenesis, there are two renal veins for each kidney: ventral and dorsal. Normally, the dorsal renal vein involutes as the anterior persists as the main renal vein in adult patients. Anatomic anomalies can occur if the involution of the dorsal veins does not occur, including retrocaval and circumaortic left renal vein and duplication of right renal vein.

Clinical Presentation

Patients with IVC anatomic aberrations are most commonly asymptomatic and the anomaly is discovered fortuitously during an imaging study ordered to assess other problems. Nevertheless, complications sometimes occur directly related to the presence of anatomic aberrations.

With retroaortic left renal vein, an increased incidence of testicular varicoceles has been reported, presumably due to compression of the left renal vein by the abdominal aorta. With the circumcaval ureter type, there could be partial right ureteral obstruction or recurrent urinary tract infection. With the absence of infrarenal IVC or entire IVC, patients may present with venous insufficiency of the lower extremities or idiopathic deep venous thrombosis. Approximately 5% of patients younger than 30 years with idiopathic deep venous thrombosis show IVC absence on CT. Almost 10% of these patients with a coexisting thrombophilia have congenital absence of the IVC.⁴

In female patients, enlarged gonadal and pelvis veins can simulate pelvic congestion syndrome. Anatomic variants of the IVC can be seen in association with other anomalies. Azygos continuation, in particular, can be associated with significant congenital heart disease.

Radiography

Plain radiographs of the abdomen and pelvis have no role in the anatomic assessment of the IVC because they are unable to differentiate the veins from other retroperitoneal soft tissues. They may provide gross information though, of the relative location of foreign bodies such as filters, and catheters installed within the IVC.

Ultrasound Imaging

Ultrasound imaging with color flow Doppler imaging can be diagnostic for a variety of IVC anomalies. The key is to properly identify the abdominal venous structures (i.e., IVC), its location, its number, and its connections. With azygous continuation of the IVC, the infrahepatic IVC can be seen draining into the azygos vein with direct hepatic venous drainage into the right atrium. With left IVC, the IVC is positioned to the left of the abdominal aorta. In duplicated IVC, two vertical venous vascular structures can be seen adjacent to and paralleling the abdominal aorta. On Doppler, one IVC will drain the left renal vein.

Circumaortic left renal vein: A circumaortic left renal vein may be difficult to see on Doppler imaging because the two veins do not join the IVC at the same level.

Retroaortic left renal vein: A retroaortic left renal vein may be difficult to see on Doppler imaging. One could see a renal vein crossing behind the abdominal aorta to join the IVC. In more complex IVC anomalies, such as duplication of IVC with retroaortic right renal vein and hemiazygos continuation of the IVC or complete absence of the IVC, ultrasonography may be unable to fully delineate all venous connections and CT or MRI may be required. A circumcaval ureter is also typically not seen on ultrasound images unless there is hydroureter.

CT Scan

CT is a very useful modality to evaluate IVC anomalies because of its ability to generate volumetric data quickly for multiplanar reformation.

Technique: To study the anatomy of the IVC, the CT protocol should include imaging of the chest, abdomen, and pelvis with the use of an intravenous iodinated contrast agent. It is recommended to ensure that there is at least a 2-minute delay between intravenous contrast administration and CT scanning because this will improve the likelihood for homogeneous enhancement of the IVC. If CT is begun at the traditional portal venous phase (65 to 70 sec delay), the infrarenal IVC may have poor luminal enhancement owing to the relatively longer delay necessary for the venous return from the pelvis and inferior extremities to the IVC. The suprarenal IVC, moreover, may show heterogeneous enhancement because of mixing of the contrast bolus returning from the renal veins.

MR

Similar anatomic detail can be seen on MRI as is seen on CT. Steady-state free precession (SSFP; also termed b-FFE, Philips Medical Systems; FIESTA, General Electric Healthcare; True-FISP, Siemens Medical Solutions) pulse sequences are “bright blood” techniques that are particularly good for illustrating abdominal veins. SSFP, especially performed in cine mode, is useful for identification of central venous thrombosis. This technique does not require the intravenous administration of gadolinium-chelate contrast agents.

“Black blood” MRI pulse sequences, in which the vessel lumen is dark secondary to the washout phenomenon (also termed flow void) associated with moving spins (i.e., flowing blood that washes out of the imaging slice prior to sampling of the echo). Examples of this technique include T4-weighted spin echo and single shot T2-weighted imaging (e.g., SSFSE, HASTE), which can provide excellent anatomic assessment almost free of motion artifacts.

Gadolinium-enhanced MRI is arguably the most reliable method to assess vascular patency. We recommend postcontrast imaging using a 3D T1-weighted gradient sequence (e.g., LAVA, THRIVE, or VIBE). Because MRI does not expose the patient to ionizing radiation, it is possible to acquire multiple series of images postcontrast injection, including axial, coronal, and sagittal planes with different timing for more homogeneous luminal enhancement.

Angiography

X-ray catheter angiography studies provide limited anatomic information. In our institution, they are used mostly for therapeutic procedures. Anatomic variants should be diagnosed prior to angiographic procedures in the IVC or otherwise may cause confusion and prolong fluoroscopic time at the time of the intervention, therefore for therapy planning purposes, we recommend the use of CT or MRI.

Reporting: Information for the Referring Physician

IVC and renal vein anatomic variants have minimal increased risk for medical complications such as thrombus or embolism, but are particularly important to identify in patients planning to undergo surgical or percutaneous interventions because their identification can aid in procedure planning and reduce likelihood of complications. Recommendations for clinicians are

Clinical Presentation

Best Imaging Modality

Contrasted MRI or CT of the abdomen and pelvis is the modality of choice for the assessment of these complex tumors.^6–8 The scanning protocol should include the right atrium of the heart as well as the entire pelvis and common femoral veins. Early postcontrast phases (arterial and portal-venous) may demonstrate heterogeneous luminal enhancement due to admixing artifacts at the level of the renal veins that can obscure tumor or produce a false positive diagnosis of IVC thrombus; therefore additional 2- to 4-minute delayed images are recommended, which will provide more homogeneous luminal enhancement for improved ability to detect the presence or absence of intraluminal tumor or thrombus.

Radiography

Although abdominal radiographs can sometimes demonstrate the presence of a large calcified retroperitoneal mass, there are no specific signs of IVC invasion on plain films and, therefore, it is very limited for retroperitoneal tumor detection and characterization.

Ultrasound Imaging

Ultrasonography can detect the presence of tumor in the IVC, but in many cases, the anatomic assessment is incomplete owing to multiple limiting factors because of characteristics of the IVC anatomy. The deep location in the abdomen requires the use of low-frequency transducers with less spatial resolution and low signal-to-noise ratio. The surrounding bowel gas and bone may obscure key segments of the IVC and its tributaries. The position of the IVC in 90-degree angle with the ultrasound beam makes the color and spectral Doppler examination equivocal and limited. In summary, although in some cases ultrasound imaging can diagnose correctly the presence of IVC tumors, most of the times conclusions are limited by the technical challenges of the anatomy and, therefore, other studies are necessary to confirm the diagnosis.

Real time gray-scale US: can demonstrate an intraluminal mass and the presence of expansion of the IVC. It can demonstrate primary liver, renal and adrenal tumor.

Intraoperative US: is useful to assess proximal extension of the tumor and possible heart involvement.

Color Doppler: Can show the absence of flow caused by the thrombus that can be partially occluding the lumen or causing complete obstruction, sometimes with presence of collateral veins. Color blooming may obscure partial thrombus.

CT

Technique: pre- and multi-phase postcontrast CT is necessary to differentiate bland nonenhancing thrombus from enhancing tumor, but both may coexist in the same patient. A chest CT should be considered to look for pulmonary metastases and/or pulmonary embolism. Abdominal and pelvic CT should be performed with 2- and 4-minute delayed phases following the intravenous administration of iodinated contrast agent to obtain homogeneous luminal enhancement. The examination should include the heart and common femoral veins. We recommend producing coronal and sagittal reconstructions to better demonstrate the extension of the tumor and its relation to other anatomic structures that can be key at the time of surgical planning.

CT Findings

Intraluminal leiomyosarcoma: presents as a tumor thrombus in the lumen of the vessel. This solid neoplasm shows contrast enhancement in postinjection images. The tumor thrombus characteristically produces expansion of the IVC and can also occlude the lumen, causing venous congestion in the proximal organs such as the liver or kidneys (Fig. 110-5). Lack of a known primary tumor suggests the diagnosis of primary leiomyosarcoma of the IVC.

FIGURE 110-5 Primary leiomyosarcoma of the IVC. A, Axial T1-weighted MRI of the abdomen demonstrates a hypointense tumor expanding the IVC lumen (arrow). T2 fat saturated MRI shows high signal in the IVC tumor (B). Contrast-enhanced CT of the abdomen in axial (C) and coronal (D) images show that the thrombus in the IVC enhances heterogeneously as well as expands the vein. The more inferior component of the thrombus does not enhance or enlarge the vein and, therefore, is consistent with bland thrombus (arrow).

Extraluminal leiomyosarcoma and other retroperitoneal neoplasms: Other retroperitoneal tumors that can occlude the IVC and its tributaries include lymphomas, metastasis (ovary, testis, uterus, and others) and primary leiomyosarcomas of predominant extraluminal growth. Often these tumors are indistinguishable from each other and only a histologic analysis can differentiate them. The presence of fat density tissue may suggest a liposarcoma. Diffuse lymphadenopathy points to lymphoma. Unfortunately, the presence of calcifications is not specific for any particular kind of retroperitoneal tumor.

Adrenocortical carcinoma: Presents as a large heterogeneous adrenal mass typically with venous invasion.¹⁰ It usually compresses and displaces adjacent organs such as the kidney or liver and it can be confused with renal cell carcinoma or hepatocellular carcinoma. For this particular point, the use of sagittal or coronal reconstructions can be useful to determine the origin of the mass. As mentioned previously, the right adrenal veins drain directly into the IVC but the left adrenal carcinoma invades the IVC through the left renal vein, potentially being confused with venous invasion from renal cell carcinoma arising from the upper pole of the left kidney.

Renal cell carcinoma: typically presents as a solid, heterogeneous renal mass that can extend into the renal veins and IVC (Fig. 110-6).^8,9 There may be gonadal vein invasion. This tumor also can display direct retroperitoneal extension and lymph node metastasis.

FIGURE 110-6 Renal cell carcinoma invading the IVC. MRI of the abdomen (A). Coronal T2 balanced steady-state free precession shows RCC thrombus extending through the left renal vein, IVC, and protruding into the right atrium of the heart. The patient has developed ascites due to partial obstruction of the hepatic veins without causing thrombosis. Arterial phase CE MRI (B) shows tumor thrombus enhancement. Five-minute delay CE MRI (C, D) images demonstrate tumor enhancement and vessel expansion—both specific signs of tumor thrombus. The primary left renal mass and the patency of the infrarenal IVC are better demonstrated in a more posterior plane (D).

Hepatocellular carcinoma: is a solid hepatic tumor that is most commonly seen in patients with cirrhosis. After contrast injection, it typically enhances in the arterial phase and washes out in the delay phase. It invades the IVC through the hepatic veins.¹¹ As other tumoral thrombus, it typically expands the veins (Fig. 110-7).

FIGURE 110-7 HCC invading the IVC through the hepatic veins. A, CECT. Sagittal reconstruction. Note the presence of a nonenhancing, nontumoral thrombus component inferior to the enhancing tumor invading the IVC. The tumor expands the vessel and extends into the right atrium. B, Coronal CECT of another patient shows HCC invading large portions of the right atrium.

MR

Technique: Although nonenhanced MRI sequences can show the presence of tumor thrombus in the IVC, pre- and post-gadolinium MRI pulse sequences are ideal for the detection, characterization, and assessment of disease extent. It also is useful to characterize the primary lesion when the tumor is originated in an adjacent organ such as the liver or kidney.

SSFP and single shot T2-weighted pulse sequences can be used to demonstrate the presence of tumor without the use of gadolinium-chelate contrast agent. Using SSFP, one can detect the presence of intraluminal tumor; using single shot T2-weighted images, one can evaluate the venous mass and its relationship with the wall of the vein and the adjacent structures. The tumor thrombus has typically a heterogeneous elevated signal on T2-weighted images. We recommend acquiring sequences in axial, coronal, and sagittal planes for better assessment of the extension of the lesion.

Multiphase, pre- and post-gadolinium-enhanced three- dimensional T1-weighted imaging with fat saturation (e.g., LAVA, THRIVE, VIBE) is a very useful MRI technique. Tissue enhancement helps to differentiate a solid tumor from nonenhancing bland thrombus. Subtraction techniques can be used to demonstrate tumoral enhancement or bland thrombus nonenhancement. Postcontrast multiphase images should be obtained: Early phase (arterial and portal-venous) can show better the solid organs in the abdomen and a late phase (2 to 4 min) for infrarenal IVC assessment. Multiplanar images (axial, coronal, and sagittal) should be obtained for better anatomic assessment.

Nuclear Medicine/PET

Primary IVC sarcoma, adrenocortical carcinoma, and renal cell carcinoma are in general FDG avid tumors in PET imaging. Therefore PET can be used to detect and characterize pulmonary or systemic metastasis in these cases. PET imaging does not have a role in hepatocellular carcinoma staging because the well differentiated hepatocellular carcinomas are not FDG avid.

Angiography

Angiographic techniques are mostly used for interventions, including biopsy, IVC stent, or filter placement and angioplasty for IVC stenosis. The invasiveness of the angiographic studies and the limited information of only intraluminal anatomy makes them a less preferred technique for purely diagnostic imaging compared with noninvasive tomographic techniques such as CT or MRI.

Reporting: Information for the Referring Physician

IVC tumors can be considered a relative emergency. Appropriate staging and detection of acute complications (i.e., pulmonary embolism, liver or renal failure) should be made and imaging plays a central role in these two tasks. It is also crucial that the chest, abdomen, and pelvis have been examined with the adequate MRI or CT protocols, otherwise the studies should be repeated.

It is very important for the surgical planning to describe accurately the proximal extension of the tumor, if there are signs of IVC wall invasion, and if there is evidence of distant metastasis. It is of main importance also to distinguish between tumor and nontumor thrombus that can coexist in the same case.

Clinical Presentation

Clinical features in IVC or hepatic stenosis include hepatomegaly, ascites, and pleural effusions. Some patients are clinically asymptomatic and imaging abnormality may be the first sign of a problem. Hepatic venous outflow obstruction presents clinically with elevated liver enzymes, Budd-Chiari syndrome, or coagulation disorders.

Imaging Indications and Algorithm

Ultrasound imaging is the modality of choice for imaging post liver transplantation patients. CT and MRI may be used as well.

Imaging Techniques and Findings

Ultrasound Imaging

On ultrasound findings, the normal hepatic vein and IVC have a triphasic waveform. Ultrasound findings in IVC thrombosis are absent flow within the vein on color Doppler with no spectral Doppler flow. An intraluminal echogenic thrombus can also be seen in complete or partial thrombosis of the IVC. In IVC stenosis, there is a three- to fourfold increase in velocity as compared to the prestenotic segment. The velocity in the IVC has to be measured at the sites of anastomosis, suprahepatic and infrahepatic, in end-to-end anastomosis and at the end-to-side anastomosis in piggy-back anastomosis (Figs. 110-9 and 110-10). A significant caval stenosis may result in reversed flow or absence of phasicity in the hepatic veins.¹⁶

FIGURE 110-9 Ultrasound imaging showing the piggy-back technique of anastomosis in transverse (A) and sagittal (B) images. Donor IVC (long white arrow) and recipient IVC (double white arrows) are shown. C, Color Doppler showing the correct site of measurement of the velocity in the piggy-back anastomosis (arrow).

FIGURE 110-10 A, Spectral Doppler showing an increased velocity in the area of anastomosis and B, monophasic waveform in the hepatic vein consistent with stenosis.

Angiography

Angiography is definitive in diagnosing IVC stenosis and can provide treatment at the same time as well. Pressure gradients can be measured in the IVC and the atrium during angiography. Percutaneous treatment for IVC stenosis and thrombosis includes angioplasty and/or stenting (Figs. 110-11 and 110-12).

FIGURE 110-11 Angiography images showing preangioplasty (A) and postangioplasty IVC (B). Stenosis is present in the preangioplasty image (arrow), and the IVC appears of normal caliber in the postangioplasty image.

FIGURE 110-12 Angiography image (A). Pre-stent placement showing the narrowed caliber of the IVC (arrow) and B, postangioplasty image showing a stent in the IVC with improved caliber.

From Clinical Presentation

The clinical differential diagnosis of IVC obstruction/stenosis post–liver transplantation includes portal hypertension, hepatic vein stenosis, portal vein stenosis, and liver transplant rejection.

From Imaging Findings

IVC compression from enlarged liver.

Medical

Diuretics may be administered but treatment is primarily interventional.

Surgical/Interventional

Percutaneous intervention using angioplasty and/or stenting.

Reporting: Information for the Referring Physician

Important information for referring physicians:

Clinical Presentation

Patients with IVC thrombosis may present with a spectrum of signs and symptoms. Patients may present with symptoms that are predominantly thrombotic in origin or predominantly embolic in nature. Additionally, the thrombotic findings are dependent on the degree of occlusion of the cava and on the location between the iliac confluence and the right atrium. The classic presentation of IVC thrombosis includes bilateral lower extremity edema with dilated, visible superficial abdominal veins. The most common clinical presentation in iliocaval compression syndrome is left lower extremity deep vein thrombosis. Rarely, a patient with IVCS can present with obstruction of venous outflow without deep vein thrombosis.

Imaging Indications and Algorithm

Presence of bilateral leg edema and pulmonary embolism are common indications for imaging the IVC.

Imaging Techniques and Findings

CT

Definitive diagnosis of venous thrombosis by CT depends on demonstration of an intraluminal thrombus. Whereas a fresh thrombus has a density similar to or higher than that of circulating blood, an old thrombus is of lower density than the surrounding blood on noncontrast CT scans. When the occlusion is complete, the involved segment remains unenhanced on postcontrast CT scans. In case of chronic occlusion, the IVC may become atrophic and calcified. In partial IVC occlusion, the thrombus is seen as a filling defect surrounded by enhanced blood. A “pseudothrombus” artifact is seen due to nonopacified blood flow mixing with enhanced blood giving an artifactual filling defect appearance (Fig. 110-13). CT has 100% sensitivity and 96% specificity in detecting DVT when compared to conventional venography (Fig. 110-14).¹⁸ In patients with May-Thurner syndrome, pelvic CT images in the transverse plane show iliac vein compression by the overlying right common iliac artery in patients with left-sided deep vein thrombosis.¹⁹ In case of complete caval obstruction, extensive venous collaterals may also be identified.

FIGURE 110-13 Axial (A) and coronal (B) postcontrast CT images showing a filling defect (arrow) in the IVC adjacent to the IVC filter (arrowhead) consistent with a thrombus.

FIGURE 110-14 Axial (A) and coronal (B) postcontrast CT shows a thrombus (arrow) in the infrarenal IVC due to extension of deep venous thrombosis. Ultrasound images showing the thrombus (double arrows) in the same patient in the popliteal vein (C) and in the common iliac vein (D). The top arrow in D indicates the patent artery adjacent to the veins.

MR

On spin-echo (SE) images, venous thrombus appears as a region of persistent intraluminal signal which can be confused with slow flowing blood which can also appear as high signal intensity. On SSFP or gradient recalled echo (GRE) images, venous thrombus appears as an area of lower signal intensity. SSFP and GRE pulse sequences are faster than SE imaging and hence are preferred if gadolinium-chelate contrast agents cannot be administered because of a contraindication.²⁰ Acquisition of SSFP (or GRE) in cine mode using ECG gating will help differentiate flow artifacts from true thrombus. On cine MR, thrombus will appear as fixed intraluminal filling defects that persist throughout the cardiac cycle. Alternatively, flow artifacts will not persist and will be seen only on a few phases of the cardiac cycle. On gadolinium-enhanced MRI, in addition to a filling defect in complete thrombosis, lack of enhancement is seen in a bland thrombus; however, enhancement is seen in a tumor thrombus (Fig. 110-15). In addition, there will be focal dilation of the vena cava in an acute thrombosis and presence of venous collateral vessels in chronic thrombosis.

FIGURE 110-15 MR showing the tumor thrombus in the IVC. A, Axial postcontrast image shows the enhancement (black arrow) within the tumor thrombus. Coronal precontrast (B) and postcontrast (C) images show the filling defect (white arrow) in the IVC with enhancement in the thrombus.

From Clinical Presentation

The differential considerations for IVC thrombosis include renal dysfunction, liver dysfunction, external compression of the IVC from tumor masses, and fluid overload.

From Imaging Findings

The main differential consideration for IVC thrombosis is normal blood flow (i.e., admixing of nonopacified blood on contrast-enhanced CT; flow artifacts from normal blood flow on MRI).

Synopsis of Treatment Options

Reporting: Information for the Referring Physician

The report to the referring physician should include comment on the following:

IVC Filters

Choice of access site depends on a patient’s anatomy, the site of venous thromboemboli, and the type of filters available. Generally, the right internal jugular vein or the right femoral vein is the preferred route, but left-sided venous approaches or approaches from arm veins can be used in some circumstances (Fig. 110-16). Ultrasound scanning can be used to confirm entry site and to guide puncture in difficult cases. After local anesthetic injection, the subcutaneous tissues are infiltrated and the vein is punctured under strict antiseptic conditions. A cavogram is performed to confirm anatomy and the presence or absence of intraluminal filling defects and to identify the renal veins and anatomical variants. Conscious sedation with midazolam and fentanyl can be used. Following the cavogram, the diameter of the IVC is calculated; most filters cannot be placed if the cava is larger than 28 mm, the exception being the bird’s nest filter. The filter is usually placed below the renal veins but can be placed in a suprarenal position when there is renal vein thrombosis or thrombus extending proximal to the renal veins, during pregnancy, and when there is thrombus proximal to an indwelling filter. The procedure usually takes less than 60 minutes.²⁵

FIGURE 110-16 IVC filter (arrow) with correct placement as seen on coronal CT reformat (A) and angiography (B).

IVC Shunts

Different types of IVC shunts include the side-to-side portocaval shunt and the mesocaval shunt.

Side-to-Side Portacaval Shunt (SSPCS). This shunt may be performed for hepatic venous obstruction due to isolated hepatic vein thrombosis (Fig. 110-17). The data on SSPCS for hepatic vein obstruction is somewhat limited—an earlier review reported only two studies with more than 10 patients each.²⁶ The reservation against performing SSPCS in patients with hepatic vein thrombosis is the likely technical difficulty in approximating the portal vein to the infrahepatic vena cava in the presence of a hypertrophied caudate lobe. Another argument is that because a portacaval shunt involves hepatic hilar dissection, it may increase the technical difficulties if a subsequent liver transplantation is needed because of progression of liver disease. Despite these reservations, excellent long-term graft patency and symptom-free survival of 81% to 94% has been reported in series from dedicated centers.

FIGURE 110-17 Ultrasound image in a patient with a portocaval shunt (A). Color Doppler image shows an area of aliasing (double arrows) in the shunt with high velocity seen on spectral Doppler (B), and stent (arrow) placed in the portocaval shunt as seen on CT (C).

Mesocaval Shunt (MCS). MCS is the preferred shunt in the setting of isolated hepatic vein thrombosis in many studies.²⁷ Advantages of MCS are its technical simplicity and avoidance of hilar dissection. The prerequisite for this shunt is a patent IVC and it provides an effective hepatic decongestion even in those patients in whom an enlarged caudate lobe presses on the IVC.²⁸ The shunt can be an autologous internal jugular vein or prosthetic (Dacron or PTFE). The main disadvantage of the Dacron grafts is high incidence (up to 50% or more in some series) of postoperative thrombosis, whereas the reported long-term patency of the internal jugular vein grafts exceeds 80%.²⁹ Reported 5-year survival after MCSs for hepatic venous outflow obstruction ranges between 57% and 95%. Because the mesocaval shunt is a partial shunt (portal vein flow is maintained), there is a low rate of encephalopathy, rebleeding, and improved quality of life.

IVC Stents

IVC stents are placed routinely to bypass areas of occlusion or stenosis (Fig. 110-18). Placement of long-standing indwelling venous catheters or creation of surgical anastomoses in patients undergoing liver transplantation increases the risk of IVC stenosis. Percutaneous stent insertion can produce rapid and sustained relief of symptoms, either as a primary treatment or in patients in whom other methods have failed or symptoms have recurred. Since this technique was first reported in 1986, it has become widely used in the palliation of IVC obstruction.

FIGURE 110-18 Stents placed in the IVC (arrow) and hepatic vein (double arrows) for stenosis in a post-liver transplantation patient.

KEY POINTS

Inferior Vena Cava

• Best diagnostic clue to the congenital anomalies of IVC is malposition or absence of parts or all of IVC.

• Circumaortic left renal vein is the most common type, followed by retroaortic left renal vein. Next most common types are duplicated IVC and left IVC; this is followed by azygos continuation of IVC.

• Best imaging diagnostic tool is CT with multiplanar reformation.

• Top differential diagnosis is adenopathy and retroperitoneal mass.

• Patients are usually asymptomatic. Those with duplicated IVC can present with recurrent PE. Those with absence of IVC can present with lower extremity venous insufficiency.

• Preoperative anatomic delineation is necessary in all cases.

Tumors of the IVC and main tributaries

• Primary versus secondary tumor invasion of the IVC

• Tumor thrombus versus nontumoral thrombosis of the IVC

• Multiphase, multiplanar contrasted CT or MRI is indicated. Include chest (heart and pulmonary arteries) and abdomen-pelvis.

• Surgical resection is the only curative treatment and can be attempted in patients without distant metastasis.

IVC complications in orthotopic liver transplantation anatomy

• Monophasic waveforms in the hepatic veins

• Increased velocity at the IVC anastomotic site

• Exclude compression from enlarged liver or other focal lesions such as fluid collection

IVC thrombosis

• Assess extent of IVC thrombosis

• Exclude presence of tumor thrombus

• Watch out for artifact from nonopacified blood