Caval Anatomy: Variants and Lesions






  • Key Points


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    Contrast-enhanced CT scanning is well suited to imaging congenital anatomic variants of the cavae as well as caval pathologies, including caval thrombi, tumors, obstructions, and occlusions.


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    Congenital variants of the cava are not uncommon and may be complex.


The cavae are large vessels with near-vertical orientation, which makes them particularly accessible for assessment by all manner of contrast-enhanced CT examinations, such as axial source imaging, as well as sagittal and coronal projections.


In addition to being diseased, both the superior (SVC) and inferior (IVC) venae cavae have congenital variants that are regularly encountered and that have clinical relevance. Familiarity with the congenital variants of IVC is important so as not to misinterpret them as adenopathy or other structures on cross-sectional imaging, particularly when the degree of venous opacification is poor. Venous anomalies often are dilated and may be tortuous, increasing the risk of surgical injury and bleeding. Preoperative identification of anomalies allows for better surgical planning and may avoid potentially disastrous errors.




Anatomy Of the Superior Vena Cava


The SVC (or precava) returns deoxygenated blood from the upper half of the body to the right atrium. Its proximal aspect is the union of the left and right brachiocephalic veins; its distal aspect is the union with the superomedial aspect of the right atrium ( Fig. 29-1 ).




Figure 29-1


Caval anatomy. IVC, inferior vena cava.


Branches and Tributaries of the Superior Vena Cava




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    Left brachiocephalic (innominate) vein



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      Left subclavian vein


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      Left internal jugular vein


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      Left superior intercostal vein



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    Right brachiocephalic (innominate) vein



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      Right subclavian vein


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      Right internal jugular vein



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    Azygos vein



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      Hemiazygos vein


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      Accessory hemiazygos vein




Congenital Variants


Persistent Left Superior Vena Cava


See Figures 29-2 through 29-6 ;



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    Incidence:



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      Isolated: 0.3% to 0.5%


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      Presence of congenital heart disease: 3% to 10%



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    Results from failure of involution of the left cardinal vein


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    The right SVC is absent in 30% of cases.


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    The left SVC usually drains into the coronary sinus, which is dilated. Rarely, the left SVC may drain into the left atrium.


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    Clinical relevance:



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      Association with congenital heart disease


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      May confer difficulty in catheterizing the right heart, in placement of pacemakers or implantable cardioverter defibrillators


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      Alters the technique of placing the heart on bypass





Figure 29-2


Multiple composite images from a cardiac CT study demonstrate bilateral superior venae cavae (SVC), with the right-sided SVC entering into the right atrium in a normal fashion. A left-sided SVC is seen entering into the coronary sinus, which is enlarged due to the presence of the left SVC.



Figure 29-3


CT ( A and C ) and cardiac MR ( B and D ) images of persistence of the left superior vena cava (SVC). A and B are corresponding CT and CMR images. The left SVC in this case enters the left atrium through the left atrial appendage. The detail is better appreciated on the CT image. C, The right SVC entering the superior right atrium. An “unroofed” coronary sinus atrial septal defect is seen as well. D, CMR perfusion image demonstrating contrast returning to the right atrium via the coronary sinus.



Figure 29-4


Serial axial contrast-enhanced ECG-gated CT scan images reveal the course of a persistent left superior vena cava (SVC). The left SVC has an unusual course and drains into the left atrial appendage ( D ). The coronary sinus is not dilated ( F ), because the left SVC does not drain into it. There is differential contrast density in the coronary sinus relative to the right atrium. The contrast density in the coronary sinus mirrors that of the left heart, suggesting a left-to-right shunt, in this case an unroofed coronary sinus. There is an incidental pulmonary embolus to the right lower lobe in this patient presenting with chest pain. See



Figure 29-5


Multiple ECG-gated CT angiographic images obtained prospectively in a 32-year-old patient with repaired tetralogy of Fallot. Bilateral superior venae cavae (SVCs) are present. A right SVC contains a small amount of contrast, showing that it forms its confluence appropriately with the right atrium. The left SVC has no visible contrast within its superior portion; as the intravenous contrast was injected into the right antecubital fossa. The lower course of the left SVC forms a confluence with the coronary sinus. The coronary sinus is dilated. Contrast does reflux from the right atrium into the terminal portion of the left SVC. Evidence of this patient’s previous transannular repair for tetralogy of Fallot also is seen. A, Dilatation of the main pulmonary artery with a small amount of pulmonary arterial calcification anteriorly. There is a right ventricular outflow tract (RVOT) patch, with prior surgical resection of RVOT muscle bundles. This is seen in close proximity to the substernal tissues. C, A small amount of calcification is seen within the high ventricular septal defect patch.



Figure 29-6


A, The four-chamber projection demonstrates a secundum atrial septal defect (ASD) with higher-attenuation left-sided contrast tracking into the right atrium through the ASD. Note the enlarged right-sided chambers, and the enlarged coronary sinus. B, Short-axis oblique projection demonstrates the superior vena cava (SVC) on the left of the image entering the right atrium, and a persistent left SVC on the right of the image and its continuity with the coronary sinus.


Double Superior Vena Cava




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    Incidence:



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      Isolated: 0.3%


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      Presence of congenital heart disease: 11%




Superior Vena Cava Agenesis and Drainage into the Inferior Vena Cava via the Azygos Vein




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    Total absence of the SVC


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    Due to lack of development of the right anterior cardinal vein


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    The azygos vein is dilated and carries blood posterior to the diaphragm to the IVC.


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    Incidence: rare



Superior Vena Cava Obstruction/Superior Vena Cava Syndrome


Caval obstruction may be partial or complete (occlusion) and may result from any combination of extrinsic compression, intramural scarring, and intraluminal thrombosis or other mass lesion. Etiologies are diverse and include:



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    Extrinsic compression:



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      By tumor: 90% of cases of SVC syndrome are due to malignant compression of the SVC, especially by:



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        Bronchogenic carcinoma


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        Lymphomas


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        Breast carcinoma



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      By ascending aortic aneurysms



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        Syphilis


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        Tuberculosis




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    Iatrogenic intraluminal thrombosis due to instrumentation of the SVC



Superior Vena Cava Stenosis


Caval stenosis is evident on contrast-enhanced CT scanning by focal narrowing and proximal venous engorgement, with or without venous collateral formation.


SVC Occlusion


SVC occlusion is evident on contrast-enhanced CT scanning by the absence of contrast enhancement within the cava. CT is able to image structures near the cava and elsewhere inside the body that may explain or suggest the cause of the obstruction. Proximal venous distention is usual. The presence of collateral vessels indicates chronicity.


Intraluminal Thrombus Versus Tumor Mass


Distinguishing thrombosis from tumor (angio) invasion may be possible and requires finding the origin of the soft tissue caval intraluminal mass. Chronic thrombosis organizes and usually contracts the cava, whereas acute thrombosis distends the cava. Indwelling lines, pacemaker wires, and implantable cardioverter defibrillator leads that are the source of thrombosis confer artifacts. Streaming artifacts from the contralateral venous drainage, and also from the azygos vein, may make it difficult to confirm thrombosis. ( Figs. 29-7 through 29-9 ; ).


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Apr 10, 2019 | Posted by in COMPUTERIZED TOMOGRAPHY | Comments Off on Caval Anatomy: Variants and Lesions

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