Cardiac Masses, Thrombi, and Tumors
Normal Variants and Masses of Uncertain Significance When an abnormally localized accumulation of dense reflectances appears on the echocardiogram, it is said to represent a mass. Echocardiographic masses may be caused by technical artifacts or anomalous structures, but they are of greatest significance in representing true lesions of the heart such as tumors, thrombi, and vegetations. Echocardiography is the procedure of choice for the detection and evaluation of cardiac mass lesions; often, it is the only modality capable of delineating small lesions such as papillary fibroelastomas.299 Accordingly, echocardiographic examinations are commonly performed to search for embolic sources, particularly in patients with cerebral ischemic events. A number of technical artifacts are capable of appearing as masses on echocardiogram. For example, side lobe signals, reverberations, and noise artifact may lead to accumulations of ultrasonic reflectance within the cavities or adjacent to the myocardium of the heart.22,23 Such structures usually lack distinct borders, do not move appropriately through the cardiac cycle, lack identifiable attachments to endocardial surfaces, and cannot be visualized in all views and at all depth settings. In seeking a way to distinguish artifacts from LV thrombi (a common clinical dilemma) the absence of wall motion abnormalities is of particular value.300 Several benign normal variant findings can be observed during echocardiographic examination and must be distinguished from pathologic lesions. Thus, many adults manifest persistence of the eustachian valve (Fig. 15–125), a thin ridge of tissue at the junction of the inferior vena cava and right atrium.301 The eustachian valve appears as a long, linear, freely mobile structure in the right atrium at the mouth of the inferior vena cava and is nearly always benign (although infective involvement has been reported).302 An additional embryonic remnant that may be seen in the posterior right atrium is the Chiari network, which typically appears as a weblike mobile structure.303 In some individuals, RVH may produce significant enlargement of the RV moderator band coursing along the interventricular septum to the apex of the RV.304 Similarly, false chordae tendineae ("heartstrings") can occasionally be visualized as linear structures spanning the LV cavity attached to endomyocardium at both ends (Fig. 15–126).305 Neither of the foregoing lesions has been conclusively associated with morbidity or mortality. On occasion, LVH or hypertrophied papillary muscles may simulate cardiac mass lesions.304 Although TEE provides enhanced sensitivity and resolution in the delineation of cardiac mass lesions, this technique may be associated with variants and artifacts of its own.
A variety of foreign bodies and iatrogenically induced anatomic alterations may be visualized on echocardiogram and must be distinguished from pathologic lesions. Intracardiac catheters, pacemaker leads (Fig. 15–127), prosthetic valves or patches, and atrial suture lines after cardiac transplantation can be visualized during echocardiographic examination. These structures are usually easily recognized due to the highly reflective properties of the foreign material, which result in bright echoes, reverberations, and shadowing behind the structures. In this regard, endomyocardial biotomes and pericardiocentesis catheters can be readily visualized by cardiac ultrasound, and echocardiography can be employed to guide procedures utilizing these instruments in lieu of fluoroscopy.306 Last, a variety of manufactured objects that have penetrated the heart have been described on echocardiography, including bullets, pellets, and nails.
Several morphologic changes involving the interatrial septum are often considered under the classification of cardiac mass lesions of uncertain significance. Aneurysms of the interatrial septum have been reported in about 1 percent of the population and are recognized on echocardiogram as a protrusion of the interatrial septum of at least 1.5 cm from its longitudinal plane dividing the left and right atrium (Fig. 15–128).307 Although usually benign, interatrial septal aneurysms are often associated with a patent foramen ovale and have been implicated as a source of cardiogenic emboli. Interatrial septal aneurysms may be detected by TTE, but they are more readily imaged by the transesophageal approach.307 Lipomatous hypertrophy of the interatrial septum, or accumulation of adipose tissue within this structure, is not an uncommon finding in elderly individuals. Lipomatous hypertrophy appears as a highly reflective thickening of the interatrial septum that typically spares the foramen ovale, thereby creating a characteristic dumbbell-shaped echocardiographic appearance.308 No significant consequences or sequelae have been attributed to lipomatous infiltration of the interatrial septum.
Intracardiac Thrombi Intracardiac thrombi occur commonly in a variety of cardiovascular disorders, may be visualized in any chamber of the heart, and frequently result in embolic events.309 The major factors that predispose to the formation of intracardiac thrombi include localized stasis of flow, low cardiac output, and cardiac injury. In addition, migration of venous thrombi may also result in intracardiac clots. The appearance of intracardiac thrombi may vary considerably, and although they are typically attached to the endocardium, unrestricted and freely mobile thrombi occasionally may be encountered (particularly in the setting of valvular stenosis which prevents exit of the thrombus from the heart). Thrombi typically have identifiable borders and may be layered and homogeneous or heterogeneous, with areas of central liquefaction (Figs. 15–129 and 15–130).310
Right Heart Thrombi within the right heart chambers may form locally or migrate from the venous circulation; they are found most commonly in the RA. As opposed to the laminar, relatively immobile nature of RA thrombi that form in situ, venous thromboemboli trapped in the RA tend to be serpentine and mobile. The potential for pulmonary embolism is high. Thrombi also can be seen within the main pulmonary arteries, although they are less well visualized by TTE than TEE.311 RV thrombi are rare but may occur with RV infarction and endomyocardial fibrosis. Their appearance is similar to that of LV thrombi. Left Atrium Left atrial thrombi occur in the setting of low cardiac output, mitral valvular disease (particularly MS), atrial fibrillation, and LA enlargement. Both TTE and TEE can detect thrombi within the main cavity of the LA (Fig. 15–131), but TEE is clearly superior for visualizing thrombi within the left atrial appendage. Since approximately 50 percent of LA thrombi are limited to the appendage, TEE is the diagnostic procedure of choice to detect this lesion.312 LA thrombi appear as discrete masses, either fixed or mobile, and are usually of homogeneous echo density (Fig. 15–52). On TEE, normal pectinate muscular ridges in the appendage must be distinguished from small thrombi. In addition, the left atrial appendage may occasionally be multilobed. Although this anatomic variant may be a risk factor for appendage thrombi, the atrial tissue separating the lobes should not be mistaken for clot.313 Left atrial thrombi are often accompanied by spontaneous echo contrast (or "smoke") within the LA. This finding, probably produced by transient aggregation of erythrocytes and plasma proteins, indicates stagnant blood flow and can occur in any cardiac chamber or the aorta. Left atrial spontaneous echo contrast, like LA thrombus, has been associated with embolic events314 and may be a marker of regional prothrombotic activity.315 On 2D imaging, the contrast signals are in constant motion and can be missed if gain settings are inappropriately low.
Left Ventricle Most LV thrombi occur in settings of abnormal systolic contraction (dilated cardiomyopathy, AMI, and chronic LV aneurysm).316 LV thrombi have been reported in up to one-half of patients with large myocardial infarctions and occur more frequently in anterior infarctions (up to 30 to 40 percent of such patients).316 Most thrombi are located in the apex300 and thus are best visualized in the apical views (Fig. 15–129). Although echocardiography is the procedure of choice for detecting LV thrombi, the technique's true sensitivity and specificity remains uncertain, since most patients included in validating studies had LV aneurysms and the echocardiographic criteria applied were subjective.316 LV thrombi may be laminar and fixed or protruding and mobile, and they may have a heterogeneous echo density (Figs. 15–129 and 15–130). Studies suggest that "immature" thrombi are often filamentous, with irregular borders, while older thrombi tend to be echodense and fixed.300,309 The echocardiographic characteristics of thrombi may influence the risk of cardiogenic embolization, as irregularly shaped, mobile, and protruding thrombi are more likely to embolize than laminar, immobile clots.309 True LV thrombi have a density distinct from the underlying myocardium, appear in multiple imaging planes, and move concordantly with the underlying myocardium. Suspected masses in areas of normally functioning myocardium are rarely thrombi. |
