Indian Journal of Radiology and Imaging Indian Journal of Radiology and Imaging

CARDIAC RADIOLOGY
Year
: 2012  |  Volume : 22  |  Issue : 1  |  Page : 40--46

Pictorial essay: Non-coronary applications of cardiac CT


Prabhakar Rajiah 
 Cardiovascular Imaging Laboratory, Imaging Institute, Cleveland Clinic Foundation, Ohio, USA

Correspondence Address:
Prabhakar Rajiah
Imaging Institute, Cleveland Clinic Foundation, Ohio
USA

Abstract

Recent advances in scanner technology have enabled computed tomography (CT) scan to evolve into a valuable tool in the noninvasive evaluation of coronary artery disease. Due to its high negative predictive value, CT can act as a gatekeeper, determining which patients require cardiac catheterization. Although mainly used for the evaluation of coronary artery disease, cardiac CT is also useful in the evaluation of various non-coronary cardiac conditions involving the pericardium, pulmonary veins, and the coronary veins and valves, as well as in the assessment of cardiomyopathies, masses, and ventricular and valvular function. This review discusses and illustrates the various non-coronary applications of cardiac CT.



How to cite this article:
Rajiah P. Pictorial essay: Non-coronary applications of cardiac CT.Indian J Radiol Imaging 2012;22:40-46


How to cite this URL:
Rajiah P. Pictorial essay: Non-coronary applications of cardiac CT. Indian J Radiol Imaging [serial online] 2012 [cited 2019 Sep 17 ];22:40-46
Available from: http://www.ijri.org/text.asp?2012/22/1/40/95403


Full Text

 Introduction



Advances in scanner technology have enhanced the ability of computed tomography (CT) scan to evaluate coronary artery disease with a high negative predictive value. [1] Cardiac CT is also increasingly used to evaluate a variety of non-coronary structures including the veins, arteries, chambers, myocardium, valves, and the pericardium. Echocardiography or magnetic resonance imaging (MRI) is the preferred first-line imaging modality for several of these conditions. However, echocardiography is operator dependent and has a limited field-of-view. MRI cannot be used in patients with contraindications, claustrophobia, or those with severe renal dysfunction. CT scan is useful as an alternative imaging tool in these scenarios and may even provide complementary information in some instances.

This review describes and illustrates the non-coronary applications of cardiac CT.

 Veins



Pulmonary veins

Recurrent atrial fibrillation is treated with radiofrequency ablation of the ectopic arrhythmogenic foci located at the veno-atrial junction of the pulmonary veins. Imaging is required prior to this procedure for the evaluation of the pulmonary veins (anatomy, branching pattern, and orientation), left atrial volume, left atrial thrombus, and the relationship of the esophagus to the left atrium. Following the procedure, imaging is required for the detection of complications such as pulmonary stenosis, thrombus, and esophago-atrial fistula. [2] CT scan has a faster turnaround time than MRI. In the electrophysiology lab, the images from volume-rendered 3D CT are combined with electrophysiological data to make an electroanatomic map, which creates a virtual 3D model that is useful for catheter navigation. [3]

Variations in pulmonary venous drainage are seen in 15-20% of the population. [2] In the conjoined pattern, more common on the left, the superior and inferior veins unite to form a single large ostium [Figure 1]A, which may make segmental isolation difficult. In the accessory pattern of drainage, accessory, small ostia are seen in addition to the normal four ostia. This is more common in the right middle lobe and the superior segment of the lower lobe. [2] Recognition of accessory veins is essential not only to ensure that these are not inadvertently injured to cause pulmonary stenosis, but also to ensure that all the veins are ablated to avoid recurrence. {Figure 1}

An early branch is located within 5 mm of the ostium of the main pulmonary vein and is prone for stenosis. Knowledge of the orientation of the veins and the size of the ostia enables determination of catheter size and orientation during the procedure, thus reducing procedure and fluoroscopy times. [4] In anomalous pulmonary veins, there is partial or total connection of the pulmonary veins to the systemic veins or the right atrium, resulting in a left-to-right shunt.

Pulmonary venous diameter and area are measured on short axis images. Ablation is difficult and avoided in pulmonary stenosis. [2] The presence of a left atrial thrombus is another contraindication to pulmonary ablation [Figure 1]B. A clear picture of the relationship between the posterior wall of the left atrium/pulmonary veins and the esophagus is essential to avoid creation of an atrio-esophageal fistula. [5]

Coronary veins

The coronary sinus or one of its tributary veins is used as an access route to the left ventricle in various transvenous procedures such as cardiac resynchronization therapy (CRT), percutaneous mitral annuloplasty, and retrograde cardioplegia. If the coronary veins are absent, a transvenous approach is not feasible and surgery may be required. The lateral and posterior cardiac veins may be congenitally absent in 1-3% of the population. [6] The left marginal and posterolateral veins may be absent in as many as 75% of patients with non-ischemic cardiomyopathy. [6],[7] A CT venography performed with the same acquisition parameters as a CT angiography, but with a slight delay to capture the venous phase, delineates the coronary venous anatomy [Figure 2]. Delayed contrast-enhanced CT can also detect the presence of extensive scar in the lateral left ventricular wall, which is a predictor of failure of CRT due to the absence of a site for mechanical activation. [7] {Figure 2}

Arteries

Lesions in the aorta, pulmonary arteries, and other vessels may be seen incidentally or evaluated using CT scan.

Aorta

Acute aortic syndrome includes dissection, intramural hematoma, and penetrating atherosclerotic ulcer. Acute aortic dissection presents with a flap dividing the vessel into a true and a false lumen. Type A dissection involves the ascending aorta [Figure 3]A, warranting surgical management, while Type B involves the arch and descending aorta and can be managed medically in the absence of complications. Intramural hematoma presents with high intramural attenuation on a non-contrast scan and with intermediate to high attenuation on a contrast-enhanced scan [Figure 3]B. and has similar clinical course as dissection. Penetrating atherosclerotic ulcer is more common in the descending thoracic aorta and is seen as focal outpouching of contrast from the aortic lumen. Aortic dilatation is diagnosed when the diameter exceeds the normal established value of that particular segment by more than 2 standard deviations (e.g., ascending aorta > 4 cm, descending aorta > 3 cm). Aortic aneurysm is diagnosed when the diameter exceeds 1.5 times the normal established value (e.g. ascending aorta > 5 cm, descending aorta > 4 cm). In aortic coarctation, there is discrete focal narrowing of the aorta, most commonly seen just distal to the left subclavian artery origin [Figure 3]C. In patients with pulmonary atresia or severe pulmonary stenosis, the lungs are supplied by major aorto-pulmonary collateral arteries (MAPCAs), which originate from the aorta or its branches [Figure 3]D. These branches have a disorganized pattern and CT scan can delineate the exact course of these branches, which is essential for planning surgeries such as unifocalization. {Figure 3}

Pulmonary arteries

Pulmonary embolism is seen as a complete or partial intraluminal filling defect in the acute stage [Figure 4]A and as a filling defect, web [Figure 4]B, or small caliber vessels in the chronic stage. Pulmonary artery hypertension may manifest as a dilated main pulmonary artery (>2.9 cm) [Figure 4]C, with features of right ventricular strain such as bowing of the inter-ventricular septum [Figure 4]D. Pulmonary arteritis presents with wall thickening and contrast enhancement. Pulmonary artery tumors are rare and mimic pulmonary emboli, but cause distension of the artery. {Figure 4}

 Cardiac Chambers



Masses

CT scan is used in the evaluation of cardiac masses, when MRI is contraindicated. It is ideal in the evaluation of calcifications and in determining arterial supply. Thrombus is the most common cardiac mass and is seen as a filling defect, more commonly in the left atrial appendage or in the left ventricle [Figure 5]A, adjacent to an infarcted or dyskinetic segment. [8] Thrombus may be confused with slow flow, but it has lower attenuation than slow flow and persists even in delayed phase images, while slow flow disappears. Lipomatous hypertrophy of the inter-atrial septum is characterized by a thick, dumb-bell shaped, fatty inter-atrial septum, with sparing of the fossa ovalis [Figure 5]B. [9] {Figure 5}

Benign neoplasms are more common in the left heart and are typically small with smooth and well-defined margins and no evidence of invasion, feeding vessel, pericardial effusion, or distal metastasis. [9] Myxoma , the most common benign neoplasm, is typically seen in the fossa ovalis as a pedunculated mass [Figure 5]C. Papillary fibroelastoma is most commonly seen on the cardiac valves. Hemangioma may have phleboliths and variable contrast enhancement. Paraganglioma shows intense contrast enhancement. Rhabdomyoma and fibroma are rare pediatric tumors. [9]

Malignant neoplasms are more common in the right heart and typically show ill-defined, infiltrative, and lobulated margins as well as evidence of invasion of adjacent structures, presence of feeding vessel, pericardial effusion, and distal metastases. Metastasis is the most common malignant mass in the heart. Pericardial infiltration is seen as effusion, thickening, or disruption. Myocardial involvement results in thickening and nodularity [Figure 6]A. Primary cardiac lymphoma is rare and may present with focal mass, diffuse infiltration, multiple nodules or pericardial effusion. Angiosarcoma is the most common type of sarcoma in the heart, with the majority seen in the right atrium [Figure 6]B. Rhabdomyosarcoma and osteosarcoma are more common in the left atrium. Leiomyosarcoma, liposarcoma, malignant fibrous histiocytoma, and synovial sarcoma are rare tumors. Mesothelioma is a primary malignant tumor of the pericardium, usually associated with asbestos exposure. [9] {Figure 6}

Congenital heart disease

MRI is the preferred modality in the evaluation of congenital defects, and CT scan is limited to patients who cannot have an MRI scan. Atrial septal defects are classified as ostium primum, ostium secundum [Figure 7]A, sinus venosus [Figure 7]B, and coronary sinus defects, based on their location in the septum. Ventricular septal defects can be membranous, muscular, and inlet or outlet types. Atrioventricular and Gerbode defects can also be seen. A patent foramen ovale is seen as a flap in the region of the fossa ovalis, with a left-to-right shunt. CT scan is useful in the morphological evaluation of septal defects prior to percutaneous repair and for the evaluation of complications following the repair.{Figure 7}

In D-transposition of the great arteries , there is ventriculo-arterial discordance, with the aorta originating from the right ventricle and the pulmonary artery originating from the left ventricle [Figure 8]A. In congenitally corrected transposition (L-transposition), there is atrio-ventricular discordance in addition to the ventriculo-arterial discordance, with the left atrium connected to the right ventricle and the right atrium to the left ventricle [Figure 8]B, C. Surgical procedures for treatment of transposition include atrial and arterial switch procedures. Tetralogy of Fallot is characterized by right ventricular outflow obstruction, right ventricular hypertrophy, ventricular septal defect, and overriding of aorta. Complete repair [Figure 8]D, E performed in these patients may be complicated by pulmonary regurgitation. [10] {Figure 8}

Valves

CT scan has a limited role in the evaluation of valvular abnormalities. It cannot provide flow information obtained with echocardiography or MRI, but can provide morphological information. A bicuspid aortic valve has only two cusps and has a characteristic fish-mouth appearance on short-axis images [Figure 9]A and systolic doming of the anterior leaflet on coronal images. In stenosis, the leaflets are thickened or calcified, with reduced opening during systole in aortic stenosis and during diastole in mitral stenosis [Figure 9]B. The valve area measured by planimetry, both in end-systole and end-diastole, can help quantifying aortic and mitral valve disease. [11] Valve calcification can be qualitatively graded as mild, moderate, or severe, or may be quantified by 3D techniques [12] with correlation seen between calcification severity and the severity of aortic stenosis. The size of the regurgitant orifice correlates directly with the grade of regurgitation. Good correlation has been shown between Multidetector CT and echocardiography in the assessment of valve area, [13] valve opening, and regurgitation. [11] Valve motion can be evaluated on retrospective ECG-gated multiphasic cine images. CT scan provides valuable information in patients being evaluated for percutaneous aortic and mitral valve procedures. CT scan is also useful in the evaluation of a prosthetic valve [Figure 10]A, which might be challenging with echocardiography and MRI. CT scan can evaluate complications such as thrombus, vegetations, abscess [Figure 10]B, pseudoaneurysm [Figure 10]C, and valve dehiscence. [14] {Figure 9}{Figure 10}

 Myocardium



Cardiomyopathy

CT scan has a limited role in the evaluation of non-ischemic cardiomyopathies and is used only when there is a contraindication to MRI. CT can help in the characterization of cardiomyopathies based on the morphology and scar pattern. Global ventricular function can be evaluated using multiphasic cine images. Regional wall motion can also be evaluated and has shown good correlation with echocardiography. [15]

In hypertrophic cardiomyopathy , asymmetric thickening of the myocardium is seen, usually involving the septum [Figure 11]A. CT scan is useful for accurate measurement of the left ventricular thickness and also in evaluating papillary muscle morphology. Patchy contrast enhancement is seen on delayed images due to interstitial fibrosis. Arrhythmogenic right ventricular dysplasia (ARVD) is characterized by fibro-fatty replacement of the right ventricular myocardium [Figure 11]B. Other features include right ventricular dilation, right ventricular systolic dysfunction, regional wall-motion abnormalities, and aneurysm. Delayed enhancement may be seen in the fibro-fatty type. In left ventricular non-compaction , prominent ventricular trabeculations are seen, with a noncompacted-to-compacted myocardium ratio >2.3:1 in diastole. [16] {Figure 11}

CT scan is also useful in the evaluation of ventricular aneurysms, particularly for pre-surgical planning [Figure 11]C. Aneurysms have all the three layers and a wide mouth, while pseudoaneurysms have only a pericardial lining and a narrow mouth. Diverticula are usually congenital and usually show synchronous contraction with the ventricles.

Pericardium

CT scan is used in the evaluation of pericardial diseases when assessment of calcification is required or when echocardiography is inconclusive and MRI cannot be performed. Pericardial effusion [Figure 12]A is detected with greater sensitivity on CT scan than echocardiography, particularly those that are loculated. Small effusions accumulate adjacent to the posterolateral left ventricular wall, while moderate effusions accumulate anterior to the right ventricle and larger effusions are seen anterior to both the right atrium and the right ventricle. Exudative effusions have higher attenuation than simple effusions. Cardiac tamponade may present with deformation and compression of the cardiac chambers, angulation of the inter-ventricular septum, and distension of the superior vena cava/inferior vena cava and reflux of contrast into the inferior vena cava/azygos vein. Cine images show collapse of the right ventricular free wall in early diastole, collapse of the right ventricular free wall during late diastole or early systole, septal rocking, sigmoid septum, and exaggerated respiratory variation of cardiac inflow. [17] {Figure 12}

In acute pericarditis, there is diffuse or focal pericardial thickening (>4 mm), usually associated with pericardial effusion and contrast enhancement [Figure 12]B. In chronic inflammatory pericarditis, the pericardium is irregularly thickened, with or without mild effusion. In chronic fibrotic pericarditis, the pericardium is thickened and calcified [Figure 12]C. Calcification in the presence of symptoms is suggestive of pericardial constriction. Other signs of pericardial constriction are tubular or conical ventricles [Figure 10]C, sigmoid septum, enlarged atria, narrow atrio-ventricular groove, dilated superior vena cava/inferior vena cava/hepatic vein, and pleural effusions. Cine images show diastolic septal bounce, abrupt cessation of diastolic filling, and exaggerated inspiratory septal flattening/reversal and tethering. Occasionally, constriction may be seen without pericardial thickening. [18],[19]

 Conclusion



Cardiac CT is increasingly being used in the evaluation of various non-coronary disease processes. CT scan is particularly useful when echocardiography is inconclusive and MRI cannot be performed due to contraindications or claustrophobia. CT scan is the ideal modality for the evaluation of calcification.

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