Visualization of Cardiac Tumors and Masses B. Wintersperger

7.12

Visualization of Cardiac Tumors and Masses B. Wintersperger

of the cardiac anatomy and morphology (Winter- sperger 2003). The large field-of-view (FoV) in a scan plane of usually 50 cm enables not only visu- alization of the heart itself but also of the surround- ing mediastinal structures and the entire chest. This may be especially valuable in patients with advanced malignant cardiac masses.

Although the work-up of patients with cardiac masses is not the primary focus of multi-slice cardiac CT imaging, this technique still provides a valuable tool in such cases and as a complementary analysis in patients who undergo examination of the coro- nary arteries. Beside the evaluation of solid cardiac tumors, there is increasing evidence that multi-slice cardiac CT is a very sensitive technique in screening for ventricular and atrial thrombi.

7.12.2

Imaging Techniques

Multi-slice CT imaging of cardiac masses is basically no different than other contrast-enhanced cardiac scan applications, such as imaging the coronary arteries or cardiac morphology in congenital heart disease. Detailed background information about multi-slice cardiac CT imaging algorithms can be found in the technical chapters of this book. How- ever, because of the dependency on the individual scanner and data acquisition settings, a few basics regarding the imaging of cardiac masses will be con- sidered here.

To benefit from the 3D capability of cardiac multi- slice cardiac CT and its ability to show dynamic information based on multi-phasic reconstructions, the use of retrospective ECG-gated scan techniques and algorithms is strongly recommended. This allows assessment of cardiac morphology not only in the axial plane but also, based on MPR, along any desired plane, including the individual cardiac axes.

Multi-slice CT allows for very thin collimated slices of 1 mm with 4-slice CT scanners and sub- millimeter with 16- and 64-slice CT scanners. Such high resolution is advantageous for the assessment of coronary arteries but is usually unnecessary for the assessment of cardiac masses. For this applica- tion, a slice thickness in the range of 2–3 mm is suf-

C o n t e n t s

7.12.1 Introduction 288 7.12.2 Imaging Techniques 290

7.12.3 Epidemiology of Cardiac Masses and Clinical Application of CT 290 7.12.3.1 Benign Cardiac Tumors 290 7.12.3.2 Cardiac Thrombi 291

7.12.3.3 Malignant Cardiac Tumors 291 7.12.4 Conclusion 293

References 295

7.12.1 Introduction

Compared to other referrals, multi-slice CT imag- ing of cardiac masses is rather uncommon. Two- dimensional echocardiography is still the modality of choice in screening for cardiac masses (Felner 1985, Salcedo 1992, Link 1995), as it represents an easy, non-invasive real-time approach with bed- side capabilities. Assuming optimal examination circumstances, 2D echocardiography can detect cardiac masses and even small masses attached to the cardiac valves as well as their impact on valve and global cardiac function within the same exam- ination (Olson 1996). However, image quality is mainly dependent on the patient’s habitus and the examiner’s skills. Restrictions arise in examining obese patients due to the resulting limited acous- tic windows, and right ventricle assessment may be hampered in patients with pulmonary emphysema.

Also, evaluation of the extra-cardiac extent of a mass might not be assessable.

Multi-slice CT imaging has been proven to gener-

ate artifact-free cross-sectional images that can be

reconstructed in any desired plane. Cardiac motion

can be frozen at any time point of the cardiac cycle

and the high spatial resolution allows assessment

ficient. This reduces the data acquisition time and enables scanning of the heart within a short breath- hold also with 4-slice CT. Nonetheless, the further increased volume coverage speed and higher tempo- ral resolution of 16- and 64-slice CT scanners results in reduced motion artifacts, a smaller amount of contrast agent, and improved visualization of the cardiac chambers due to the absence of contrast artifacts in the right heart. Also, coronary or val- vular disease often goes along with the presence of benign masses and it is therefore desirable to assess all pathologies in one examination. Moreover, as cardiac masses may cause arrhythmia and atrial fibrillation, high temporal resolution for adequate image quality becomes very important (Fig. 7.86).

With overlapping slice reconstruction, MPR can be used to demonstrate the exact location and extent of masses and tumors. In the follow-up of cardiac

113bpm 111bpm 75bpm 117bpm 115bpm 97bpm 80bpm 115bpm

Fig. 7.86a–c. 4-slice CT examination of a patient with a primary osteosarcoma in the left atrium (variable heart rate 75–122 bpm).

ECG-gated reconstruction in systole (0% of the RR-interval) allows visualization of the tumor and the proximal coronary arter- ies. Motion artifacts are present due to the limited temporal resolution of 4-slice CT (125–250 ms) but visualization of the lesion is still suffi cient. a Tumor in the left atrium (arrow) in sagittal MPR. b Tumor in the left atrium and abnormal right coronary artery (arrow) in 3D VRT. c ECG signal showing rapidly changing heart rate

a b

c

tumors, even non ECG-gated multi-slice CT scan- ning may be used to show gross tumor progression and pulmonary metastasis in malignant disease.

Multi-slice CT offers the potential to depict spe- cific features, such as fatty tissue of mass calcifica- tion, even on non-contrast-enhanced scans. How- ever, exact allocation of mass boundaries and mass depiction or exclusion requires the use of iodated contrast agent. Optimized protocols for contrast injection have been extensively published and have primarily focused on coronary artery assessment.

On 16- and 64-slice CT, such protocols enable a high

degree of opacification of the left ventricle and coro-

nary artery while restricting the amount of contrast

within the right atrium and ventricle in order to avoid

high-contrast streak artifacts (Wintersperger

2003). However, for mass depiction and differential

diagnosis, the opacification of all cardiac chambers

is mandatory. Appropriate visualization of the right atrium and the ventricles can be achieved with dif- ferent scan and injection regimens:

• Scanning during the second pass of the contrast agent (lower overall opacifi cation)

• Change of injection protocol using a different low-density chaser bolus (Table 7.15)

Nevertheless, the right atrium will still remain the focus of artifacts that may also be caused by the influx of non-opacified blood from the inferior vena cava.

7.12.3

Epidemiology of Cardiac Masses and Clinical Application of CT

Cardiac masses have to be differentiated from pri- mary and secondary tumors. While primary cardiac tumors arise within the heart itself, secondary tumors are most commonly due to metastasis of malignan- cies primarily located outside the heart or to direct tumor spread and invasion of masses located adjacent to the heart (e.g., bronchogenic carcinoma). Second- ary cardiac tumors are about 20 to 40 times more fre- quent than primary ones, which show a prevalence in the range of 0.0017–0.33% (Burke 1995). In addition to the evaluation of cardiac neoplasms, multi-slice CT imaging is also increasingly being used in the suspicion of cardiac thrombi.

7.12.3.1

Benign Cardiac Tumors

About two-thirds of all primary cardiac tumors are benign, and half of these are cardiac myxomas

(Burke 1995). Other benign tumors are papillary fibroelastoma (~8%), fibroma (~5%), and lipoma (~4%) (Burke 1995). In children, rhabodomyoma accounts for the majority of such tumors.

Although cardiac myxomas can be found in any cardiac chamber; in about ~75% of patients they are located in the left atrium (Fig. 7.87). Another 20%

of myxomas are located within the right atrium, only 5% arise within either the left or the right ven- tricle, and in very rare instances myxomas can be found at multiple locations or they may be associ- ated with the Carney complex (autosomal dominant syndrome) (Carney 1985). Myxomas usually show a heterogeneous low attenuation sometimes in con- junction with calcification due to regressive changes (Tsuchiya 1984) (Fig. 7.87). Especially within the left atrium, they are usually attached to the oval fossa and often present with a stalk, allowing them to move during the cardiac cycle. With the use of multi-phase reconstructions and cine mode image display, the mobility of myxomas and possible mitral valve protrusion can be depicted in multi-slice CT (Feuchtner 2004).

Although recently published data of multi-slice CT reported the depiction of even small valvular pathologies (Willmann 2002a, Willmann 2002b), in the depiction of papillary fibroelastomas, which are usually attached to cardiac valves (usually < 1 cm in diameter), echocardiography is still superior to multi-slice CT. As this tumor entity may cause recur- rent embolic events due to adherent thromboembolic material, multi-slice cardiac CT may be helpful to exclude thrombi within the cardiac cavities.

Lipomatous tumors are usually readily diagnosed by CT based on the specific imaging features of fatty tissue. However, with respect to the pathology find- ings, two different entities have to be differentiated:

Table 7.15. Injection regimens for 16-slice CT cardiac imaging (based on 300 mg iodine/ml). CTA contrast timing, CTA CT angiography

Purpose of study CTA only CTA/tumor/function

Test bolus/bolus triggering (“CareBolus”)

Delay +6 s +10 s

Volume 100 ml 120 ml

Flow rate ±4 ml/s (1.2 g/s) ±5 ml/s (1.5 g/s)

Bolus chaser 50 ml NaCl 50 ml NaCl

• Lipomas

• Lipomatous hypertrophy of the interatrial septum

Lipomas are usually found on the epicardial sur- face but may also be intracavitary and may present at any site of the atria or ventricles. Lipomatous hypertrophy consists of accumulated fatty tissue of more than 2 cm within the interatrial septum and usually sparing the oval fossa. Based on the tissue features, these tumors can be seen in non-enhanced scans (Kamiya 1990, Hayashi 1996).

In addition to the above-mentioned solid tumors, pericardial cysts represent a benign lesion that needs to be differentiated from other tumors.

7.12.3.2

Cardiac Thrombi

Intracardiac thrombi may be caused by a variety of different pathologies and may occur in any car- diac chamber. They are responsible for about 15%

of all ischemic strokes and their presence represents a major risk factor for stroke. Early identification with subsequent therapy is therefore of paramount importance.

Besides other causes of cardiac thrombi, espe- cially in patients with artificial devices (e.g., pros-

thetic valves, pacemakers), atrial fibrillation or wall motion abnormalities are known risk factors.

Thrombi primarily present as filling defects within opacified cardiac chambers and may have different appearances depending on their location (Fig. 7.88, 7.89). While thrombi due to wall motion abnormali- ties within the ventricles (most commonly, within the left ventricle) usually are crescent-shaped when located next to infarcted or abnormal myocardial wall segments (often within the apex) (Fig. 7.88), clots within the atria usually presents as round or oval-shaped, solid, low-density masses. In the atria, they may often be found within the atrial appendages (Fig. 7.89). Compared to echocardiography, the ben- efits of multi-slice CT are its large field of view and mostly patient-independent image quality. Cardiac thrombi may even be easily visualized in non-ECG- gated routine chest CT examinations (Fig. 7.89).

7.12.3.3

Malignant Cardiac Tumors

Compared to secondary cardiac tumors, primary cardiac malignancies are rather rare. Of the car- diac primary masses, only about 25% are malignant (Burke 1995). They are often asymptomatic until they become large, and even then they produce non- specific symptoms (Araoz 1999). Early depiction of

Fig. 7.87. Retrospectively cardiac gated 16-slice CT of cardiac myxomas within the left atrium (a) and right atrium (b). Both myxomas (arrows) show a typical, rather low attenuation; note the small calcifi cations (b)

a b

Fig. 7.88a,b. Cardiac 16-slice CT examination of a patient after myocardial infarction. The ventricular anatomy is displayed in two axial levels (a, b). At the apex, a crescent-shaped low-density rim consistent with a ventricular thrombus (arrows) can be identifi ed. The intracavitary structure (arrowhead) represents the posterior papillary muscle

LV RV

a b

Fig. 7.89. Non ECG-gated 4-slice CT scan of the chest with a low-density structure within the left atrial appendage (arrowheads), which, based on chronic atrial fi brillation, rep- resents an atrial thrombus. AA Ascending aorta, DA descend- ing aorta

AA PA

DA

cardiac malignancies allows conservative treatment to be initiated sooner and the need for more radical surgical treatment, including heart transplantation, to be recognized earlier (Uberfuhr 2002). Multi- slice CT can be used to accurately image the heart and the surrounding mediastinum and therefore to evaluate the extent of disease. Angiosarcoma repre- sents the most common cardiac sarcoma (~35–40%) and is usually located within the right atrium (~75%

of patients) (Janigan 1986). Based on its composi- tion, this tumor usually shows contrast enhance- ment, which may be combined with areas of necro- sis. In addition, angiosarcoma tends to invade the pericardium, which might be demonstrated by peri- cardial effusion (Figs. 7.90, 7.91).

Rhabdomyosarcomas do not show a predominant

location within the heart. They can usually be well-

differentiated from the myocardium on enhanced

scans. Furthermore, they may invade the cardiac

valves and tend to recur after resection. There are a

number of other malignant entities of primary car-

diac tumors that also may show predominant loca-

RVOT RV

LV

Fig. 7.90a, b. Patient with a very large angiosarcoma arising from the right atrium, examined with 16-slice CT. The cardiac anatomy is displayed in two axial levels (a, b).The mass already invades the pericardial sac, as evidenced by pericardial effusion (arrowheads). RVOT Right ventricular outfl ow tract

a b

tions (Table 7.16). Secondary cardiac malignancies, such as metastatic disease or direct tumor invasion from primary lesions adjacent to the heart, often have imaging features similar to those of the pri- mary tumor.

In the setting of malignant cardiac disease, multi- slice CT is often used not only for primary diagnosis but also for follow-up after chemotherapy, resection, or even cardiac transplantation. To obtain detailed information on the primary lesion itself, ECG gating is recommended, whereas non ECG-gated tech- niques are adequate for staging examinations in the assessment of metastatic lesions from primary car- diac tumors.

7.12.4 Conclusion

Multi-slice cardiac CT is a promising clinical tool in the assessment of cardiac masses. The use of this modality in cardiac imaging is rapidly growing,

and its application in imaging cardiac masses and thrombi certainly indicates a valuable niche. Since the requirements are less demanding than those of coronary CTA, adequate results can be achieved with less sophisticated multi-slice CT scanner gen- erations. However, as a prerequisite for cardiac CT imaging, ECG-based data-acquisition strategies and algorithms are necessary. The higher tempo- ral resolution and faster coverage of the newer 16- and 64-slice CT scanners can reduce the volume of contrast agent that is required and allows evalu- ation of patients with higher and irregular heart rates (Fig. 7.92). The acquisition of 3D data sets even allows for multi-planar imaging of cardiac tumors.

While multi-slice CT might be inferior to MRI in the

exact evaluation of the tumor entity, it is superior to

in staging of the primary tumor and in identifying

possible metastasis within the chest and abdomen.

Fig. 7.91a–c. Axial 16-slice CT images of a patient with noteworthy irregular pericar- dial thickening (arrows) and pericardial ef- fusion (arrowheads). The cardiac anatomy is displayed in three different axial levels (a, b, c). Biopsy revealed carcinomatous inva- sion consistent with metastasis of a small- cell bronchogenic carcinoma. The small primary tumor could be depicted on an additional scan within the left upper lobe

a b

c

Table 7.16. Overview of the most frequent cardiac tumors: frequency and common location [adapted from Burke (1995) and Araoz (1999, 2000)]

Entity Characteristic Approximate frequency (%)

Most common location

Myxoma Benign ~29 Left atrium

Angiosarcoma Malignant ~9 Right atrium

Fibroelastoma Benign ~8 Cardiac valves

Rhabdomyoma Benign ~5 Ventricles

Fibroma Malignant ~5 Ventricles

Lipoma Benign ~4 No predominance

Osteosarcoma Malignant ~3 Left atrium

Leimyosarcoma Malignant ~3 Left atrium

Rhabdomyosarcoma Malignant ~2 No predominance

Lymphoma Malignant ~2 Right atrium

Fig. 7.92a,b. 64-slice CT examination of a patient with a heart rate of 89–97 bpm during the scan. A shorter contrast delay time was selected such that both left and right ventricles show enhancement. Axial slice (a) and MPR (b) reveal a thrombus in the right ventricle (arrow). The fast rotation speed of 0.33 s enables high temporal resolution and image reconstruction free of motion artifacts

a b

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