Myxoma is the most common primary cardiac tumor, accounting for 25-50 % of cases. It typically affects middle-aged adults, 30-60 years of age, with a higher prevalence in women [10]. A majority (60-75 %) of cases are located in the left atrium attached to the fossa ovalis by a thin stalk, though less common locations include the right atrium (15-20 %), inferior vena cava, ventricles, and the valve leaflets [11]. Myxomas are solitary tumors that have a low risk of recurrence following surgical resection. However, multiple myxomas and myxomas with an atypical location have a higher risk of recurrence. These are more common in younger men and in several familial syndromes accounting for 10 % of cases [12, 13]:

On cardiac CT, approximately two-thirds of myxomas are ovoid with a smooth or lobular shape, with the remainder villous in appearance. When visualized on non-contrast CT, they typically appear hypodense, consistent with blood, and may demonstrate calcifications more often in the right atrial location (Fig. 1). On contrast-enhanced cardiac CT, myxomas appear as intracavitary filling defects with heterogeneous contrast enhancement, though the intensity may be variable depending on their chronicity and whether necrosis or hemorrhage is present. Often mobile on cine ECG gated imaging, myxomas may prolapse across the atrioventricular valves causing outflow tract obstruction depending on their size and location. When symptoms or peripheral emboli occur, surgical removal is often required.

Lipoma is the second most common primary benign tumor and accounts for approximately 10 % of primary cardiac tumors [8]. Lipomas commonly occur in middle-aged and older adults. Lipomas are encapsulated, well-circumscribed tumors consisting of mature adipocytes that can occur anywhere in the heart (Fig. 2). Approximately 50 % arise in the epicardial or mid-myocardial layers, while the other half are subendocardial, where they create filling defects with a homogenous appearance of fat attenuation (density < -50 Hounsfield units [HU]). They can occasionally be visible as thin septations on cardiac CT. Although most are solitary tumors, multiple cardiac lipomas can occur and have been described in patients with tuberous sclerosis [10]. Classically, lipomas are benign and slow growing, but depending on their location, lipomas may rarely cause a variety of complications to include compression of the coronary arteries or pericardial space (subepicardial), outflow obstruction (subendocardial), or arrhythmias (intra-myocardial).

Papillary fibroelastoma is the third most common primary benign cardiac tumor with an incidence of up to 0.33 % in autopsy series [14]. Papillary fibroelastomas account for approximately 75 % of all cardiac valvular tumors and affect men and women equally with a mean age of 60 years [15]. They are characterized by a collection of avascular fronds of dense connective tissue lined by endothelium and may arise from any endocardial surface, though the majority are found on the aortic and mitral valves. Most papillary fibroelastomas are solitary and small with an average diameter of 10 mm. However, some are mobile with a stalk and appear more likely to give rise to embolism [14]. Though most patients are asymptomatic, patients may experience cerebral embolic symptoms, such as transient ischemic attacks or strokes, or angina from coronary ostial obstruction from aortic valve lesions. Echocardiography is the preferred means for evaluation. Papillary fibroelastomas may be difficult to identify on cardiac CT due to their small size, pronounced mobility, and lack of calcification. If visible in cardiac CT, papillary fibroelastomas appear hypodense with irregular borders attached by a thin stalk (Fig. 3) and mobile on cine ECG gated imaging.

Cardiac teratoma is a rare, primary benign germ cell tumor that typically affects infants and children. Over 90 % of cardiac teratomas involve the pericardium with a predilection for pericardial effusions resulting in tamponade and/or compression of right-sided vascular structures (superior vena cava, right atrium, and pulmonary artery) [1, 2]. Cardiac teratomas contain derivatives of all three germ layers, with mature endodermal, mesodermal, and neuroectodermal elements [2]. On CT, they appear as multicystic, heterogeneous tumors typically with an associated pericardial effusion (Fig. 4) [16]. Lipid or calcific densities can also be present on CT which often provide useful clues to the diagnosis. Cardiac CT may demonstrate their intrapericardial location, extent, and relation to vascular structures to which they are adherent, assisting planned surgical interventions [16].

Malignant cardiac tumors are most often a result of metastatic disease arising by direct extension of adjacent organs or spread via hematogenous, lymphatic, or intracavitary routes [1]. The most common malignancies metastatic to the heart originate from the lung (35-40 %), followed by breast (10 %) and hematologic (10-20 %) carcinomas. Melanoma has the greatest propensity to metastasize to the heart, but it is often found late in the disease process [18•]. Other primary sites of origin include renal, hepatic, adrenal, and thyroid. The most frequent location of metastasis is the pericardium (65-70 %), followed by epicardium (25-35 %) and myocardium (30 %). Endocardial or intracavitary involvement is rarely observed (3.5 % of cases) [18•].

Cardiac CT offers several advantages for the evaluation of metastatic cardiac involvement. Primarily, cardiac CT offers the ability to image direct tumor extension and extracardiac involvement with both three-dimensional reconstruction capability and superior spatial resolution. On cardiac CT, pericardial metastasis can appear as pericardial thickening, disruption, or effusion. Myocardial involvement typically demonstrates thickening and nodularity. Solid tumors often demonstrate enhancement following the administration of intravenous contrast.

Angiosarcoma is the most common primary cardiac malignant tumor and is comprised of cells that develop multiple, irregular vascular channels. The primary site of origin is the right atrial free wall in 80 % of cases and less commonly the right ventricle or pericardium [19]. The tumor morphology typically consists of a large, multilobar mass with a heterogeneous composition that spreads along the epicardial surface and replaces the right atrial wall. Given the bulky nature, the tumor may comprise the majority of the right atrium and involve the right coronary artery leading to rupture [20]. These tumors may also be localized to the pericardium and often invade adjacent cardiac structures leading to cardiomegaly and recurrent pericardial effusions [21].

Cardiac CT allows evaluation of the tumor burden and vascularity to help distinguish this rare malignant tumor (Fig. 5). The tumor typically is characterized by a broad-based attachment with a hematogeneous connection between the right atrium and the tumor cavity which may often be identified on early imaging. Delayed imaging allows for better visualization of the tumor cavity given late contrast enhancement. The tumor is grossly hemorrhagic and often heterogeneous in appearance given the scattered areas of non-enhancing necrosis. Additionally, invasion to adjacent structures including the myocardium, pericardium, mediastinum, great vessels, and pulmonary metastasis may be identified. With pericardial involvement, there is usually “sheet-like” thickening due to the distribution and arrangement of tumor cells, in contrast to the nodular appearance seen with rhabdomyosarcomas. Pericardial and pulmonary effusions are also readily observed.

Rhabdomyosarcoma is the second most common primary malignant tumor. It accounts for 4-7 % of cardiac sarcomas and remains the most common pediatric cardiac malignancy [1]. It is a malignant tumor of striated muscle that always involves the myocardium. In contrast to angiosarcomas, rhabdomyosarcomas may arise from any location with no predilection for a specific cavity as 60 % of cases involve multiple sites of origin [22]. Additionally, the tumors may invade the pericardial space with a characteristic nodular appearance [23].

Rhabdomyosarcomas appear as large, infiltrative masses that may surround a central area of necrosis on cardiac CT (Fig. 6). They may invade the epicardial fat, valves, or surrounding myocardium. The masses are intracavitary with irregular borders and low attenuation that may appear as thickening of the myocardium [10]. They may also appear as a hemorrhagic mass replacing the pericardium. Cardiac CT is useful for identifying any extracardiac extension of the tumor as well as distant metastasis, common to the lung parenchyma, thoracic lymph nodes, mediastinum, or spine [22].

Lipomatous hypertrophy of the interatrial septum (LHIAS) is an increasingly recognized, benign incidental finding with a prevalence of 1-8 % in the general population [24]. Incidence increases with age and body mass index. It occurs more frequently in women and those with a history of systemic steroid use [24]. Findings consistent with LHIAS on cardiac CT include a “dumbbell-shaped” mass involving the interatrial septum with sparing of the fossa ovalis, a homogenous appearance with sharp margins, fatty attenuation (density < -50 HU), and no or minimal contrast enhancement (Fig. 7). Lipomatous hypertrophy of the interatrial septum typically follows a benign course though associations with supraventricular arrhythmias, sudden cardiac death, and extensive impairment on venous return requiring surgical resection have been described [24, 26].

Although there is no definitive diagnostic criteria for the diagnosis of LHIAS, an interatrial septal thickness >20 mm is often used, while a septal thickness exceeding 30 mm may have a greater association with supraventricular arrhythmias [27]. It is important to note that areas of lipomatous hypertrophy contain brown fat and, therefore, may appear as FDG-avid (“hot”) on PET scans. Though rare, liposarcoma should be considered as a differential diagnosis, especially when intra-mass calcification or enhancement is present or in cases with rapid growth and involvement beyond the interatrial septum. Other causes of fat containing cardiac lesions include fatty metaplasia due to remote myocardial infarction, cardiac lipoma and arrhythmogenic right ventricular cardiomyopathy/dysplasia.

Thrombus accounts for the most commonly encountered intracardiac mass [28]. It can occur in any of the cardiac chambers, though it most often involves the left-sided structures. Thrombus formation can be caused by hypercoagulable states, systolic dysfunction with wall motion abnormalities, atrial fibrillation, or artificial devices. It typically appears as a hypodense, low-attenuation filling defect in a contrast pool within a cardiac chamber and may be differentiated from primary and secondary tumors by knowledge of predisposing risk factors, attachment location, shape, and lack of mobility [29•].

Cardiac CT has very high sensitivity for excluding thrombus of the left atrial appendage but findings of low attenuation in the left atrial appendage (LAA) are not specific to thrombus as this often represents circulatory stasis, an incomplete mixing of contrast material and blood. This “pseudo” filling defect may mimic thrombus, especially in low-flow states [30•]. However, delayed imaging of the LAA may significantly improve the specificity to distinguish thrombus from circulatory stasis [31]. For example, a ratio of LAA attenuation to the ascending aorta > 0.75 on delayed cardiac CT images performed 30 seconds following first-pass contrast imaging can help differentiate thrombus from circulatory stasis with a high negative predictive value [32].

Left ventricular thrombi are often located in an area of myocardial hypokinesis, dyskinesia or aneurysm formation. They are frequently crescent-shaped filling defects with broad based attachments (Fig. 8). However, a pedunculated appearance has been observed and can mimic myxoma [33]. Chronic thrombi may develop spotty calcifications, though this feature has not been shown to significantly differentiate thrombus from myxoma. Thrombus within the left ventricle may be distinguished from myocardium by lower attenuation characteristics with a threshold of 65 HU providing a sensitivity and specificity of 94 % and 97 %, respectively [29•]. Right ventricular thrombus is a rare finding and usually associated with intravenous catheters, pulmonary embolism, or pulmonary embolism in transit. They have also been associated with arrhythmogenic right ventricular dysplasia, Bechet’s disease, metastatic disease, and trauma [28].

In addition to intracardiac thrombus formation, the development of left ventricular pseudoaneurysm as a complication of a large myocardial infarction may present as a cardiac mass on echocardiography and can be easily distinguished using cardiac CT (Fig. 9).

Pericardial cysts are benign, congenital lesions that account for 7 % of all mediastinal tumors [35]. Over 75 % are located within the cardiophrenic spaces, the majority of which have a right-sided predominance. This anatomic location helps to distinguish pericardial cysts from other similar findings to include bronchogenic cysts, thymic cysts, and cardiac teratomas. Additionally, with pericardial cysts, there is no connection with the pericardial space, unlike that of pericardial diverticulae. On cardiac CT, pericardial cysts are thin-walled structures that are sharply demarcated, lack septae, and have a homogenous appearance (Fig. 10). They are non-enhancing lesions with intravenous contrast administration and have attenuation similar to water (-10 to 20 HU) [36].

Cardiac CT has demonstrated to be highly accurate in identifying valvular vegetations, with a sensitivity of 97 % and specificity of 88 % as compared to transesophageal echocardiography [37]. On cardiac CT, vegetations appear as low-attenuation masses usually involving the valve leaflet free edge (Fig. 11). As a result, vegetations can lead to valvular destruction and/or dysfunction [38] and cardiac CT is particularly helpful in identifying perivalvular complications, such as perivalvular abscess formation, valve perforation, aortic pseudoaneurysms or extracardiac manifestations, such as septic emboli to the lung parenchyma.

The crista terminalis is a common mimicker of cardiac tumors when seen on cardiac CT and can be mistaken for a right atrial mass or thrombus. The crista terminalis is a smooth-surfaced, linear fibromuscular structure, with a vertical orientation and crescent shape running along the posterior wall of the right atrium from the superior vena cava to the inferior vena cava (Fig. 12). It separates the smooth sinus venosus portion of the right atrium from the trabeculated right atrial tissue and right atrial appendage. Regression is inconsistent among individuals resulting in a significant variation in the degree of fibromuscular extension. It is most notable when triphasic contrast injection protocols are used for cardiac CT. It can be distinguished on cardiac CT as a focal, low-density attenuation similar to fat.