Forty-three consecutive patients (32 men, 11 women; mean age, 62 ± 19 years) with newly diagnosed non-cardiac malignancy showing cardiac or pericardial ¹⁸F-FDG uptake on oncologic whole-body PET/CT who underwent TTE within 1 month of PET/CT were retrospectively reviewed. The present study was approved by the Institutional Review Board and conducted with ethical principles of the Declaration of Helsinki. Written informed consent was obtained from all patients before enrollment.

The primary tumors of all patients were histopathologically confirmed by analysis of surgically resected tumor or tumor biopsies. Patients with previous history of primary cardiac tumor or cardiac surgery, coronary artery disease, atrial fibrillation, significant valvular heart disease, chronic obstructive pulmonary disease, acute infection or sepsis and poor image quality were excluded.

All scans were obtained using an integrated PET/CT inline system, either Biograph Duo or Biograph TruePoint (Siemens Medical Solutions, Knoxville, TN, USA). All patients fasted for at least 6h before the PET/CT study. Approximately 1h before PET/CT, each patient received an injection of 370-555 MBq of ¹⁸F-FDG. No patients had blood glucose levels > 130 mg/dL before the injection. There were 6-8 bed positions, and acquisition time was 2-3 min per bed position. Non contrast-enhanced CT was performed from the base of the skull to the upper thighs for attenuation correction and diagnosis (130kVp, 80mA, and 5-mm slice thickness; 120kVp, 50mA, and 5-mm slice thickness). PET immediately followed over the same body region, and images were reconstructed using a standard ordered-subset expectation maximization (OSEM) algorithm. The axial spatial resolution was 6.5 or 4.5mm at the center of the field of view.

All PET/CT images were reviewed at a workstation with fusion software (Syngo; Siemens Medical Solutions, Knoxville, TN, USA) that provided multi-planar reformatted images and displayed PET images after attenuation correction, CT images, and PET/CT fusion image. CT images were used to identify the location and morphological features of the lesion, in addition to its relation to surrounding tissues. ¹⁸F-FDG uptake in cardiac and pericardial lesions was quantified by calculating the maximum standardized uptake values (SUV_max), which were obtained by normalizing the tissue concentration of FDG activity and patient weight. All PET/CT scans were reviewed and interpreted by 2 board certified nuclear medicine physicians who were blinded to the clinical data and the applied imaging convention.

All ultrasound examinations were performed with a commercially available echocardiographic device (vivid 7 [GE Vingmed Ultrasound AS, Horten, Norway], with a 2.5-MHz phased array probe). Standard M-mode, two-dimensional (2D), and color Doppler measurements were obtained according to the American Society of Echocardiography (ASE) recommendations.17)18)19) Briefly, echocardiographic data included morphology, size, location and echogenicity of metastatic lesions. Pericardial thickness greater than 4mm was defined as pericardial thickening. Left ventricular (LV) wall thickness and chamber dimension were measured from 2D-guided M-mode echocardiography. Regional LV myocardial wall motion was visually estimated by examining LV myocardial wall thickness and was classified as normal (normal wall thickening and motion), hypokinesia (reduced wall thickening and motion), and akinesia (absence of wall thickening and motion). Respiratory variation of ≥ 25% in mitral inflow peak early (E) velocity with abnormal septal notching or abrupt diastolic flattening of the posterior wall was considered diagnostic of constrictive pericarditis. Pulmonary venous (PV) velocities were also recorded, and monophasic flow or flow velocities > 1.6 m/s were regarded as functionally significant obstructions. Right ventricular (RV) chamber dimension and wall thickness were measured from the apical four-chamber view and subcostal view, respectively. All echocardiographic examinations were performed by skilled sonographers and interpreted by experienced cardiologists who were blinded to clinical information of the study population.

Data were analyzed using SPSS 18 software (SPSS, Inc., Chicago, IL. USA). Continuous variables were presented as the mean ± standard deviation (SD), and categorical data were presented as frequency percentages. Group comparison of mean SUV_max was performed by Mann-Whitney U test. A p value < 0.05 was considered statistically significant.

Although primary tumors tended to have a higher mean SUV_max than those of metastatic lesions in the heart, the difference was not statistically significant (Figure 1). Of 43 patients, 33 patients (75.0%) had only one metastatic FDG uptake, including the pericardium in 29 patients, myocardium in three patients, and cardiac chamber in one patient. Among the rest, there were seven cases (16.3%) with FDG uptake in two sites (cardiac chamber and great vessel in five patients, pericardium and myocardium in two patients) and three cases (6.9%) with FDG uptake in three sites (myocardium, cardiac chamber, and great vessels in two patients, and pericardium, cardiac chamber, and great vessel in one patient) (Table 2).

Among study population, pericardial effusion was the most common echocardiographic finding (22/43, 51.2%) in concordance with ¹⁸F-FDG uptake on PET/CT. Table 3 shows echocardiographic features according to the site of FDG uptake. Examples of each site are shown in Figure 2.

Of 32 patients with pericardial FDG uptake, 25 patients (78.1%) showed pericardial abnormalities including pericardial effusion (88.0%), intrapericardial mass or materials (40.0%), pericardial thickening (36.0%), hyperechogenicity of the myopericardium (24.0%), decreased sliding motion of the pericardium (12.0%), and constrictive pericarditis (8.0%). Despite only two cases showed pericardial and myocardial FDG uptakes simultaneously, 6 patients (18.8%) demonstrated myocardial abnormalities such as regional wall motion abnormality (RWMA) (66.7%) and increased myocardial wall thickness (33.3%). Of 29 cases with FDG uptake limited to the pericardium, 17 cases (58.6%) showed pericardial abnormalities on TTE and their mean SUV_max was not significantly different from that of others with normal echocardiogram (n=7) (7.4 ± 4.7 vs. 6.4 ± 4.8, p = 0.684) (data not shown). When comparing the mean SUV_max of pericardial FDG uptake lesions according to the type of abnormal echocardiographic features, lesions with RWMA (14.3 ± 4.7 vs. 6.4 ± 4.0, p = 0.004) or constrictive pericarditis (13.1 ± 3.4 vs. 6.6 ± 4.1, p = 0.021) had significantly higher mean SUV_max than those without. Furthermore, lesions showing pericardial thickening (8.4 ± 6.1 vs. 6.8 ± 4.1, p = 0.433) or increased pericardial echogenicity (10.1 ± 5.9 vs. 6.7 ± 4.3, p = 0.138) were more likely to have higher mean SUV_max. However, the presence of pericardial effusion or intrapericardial materials was not associated with mean SUV_max (Figure 3).

Of seven cases with myocardial ¹⁸F-FDG uptake, 6 patients (85.7%) revealed pericardial abnormalities such as pericardial effusion (66.7%), hyperechogenicity of the myopericardium (33.3%), and others (Intrapericardial mass or materials, pericardial thickening, decreased sliding motion of the pericardium, constrictive pericarditis in one patient each). Among 5 patients showing myocardial abnormalities on TTE (71.4%), RWMA in 4 cases (80.0%) and increased myocardial wall thickness in 3 cases (60.0%) were found.

All nine cases with cardiac chamber ¹⁸F-FDG uptake revealed a mass in the cardiac chambers including the RA (6/9, 66.7%), RV outflow tract (1/9, 11.1%), RV (1/9, 11.1%), and LA (2/9, 22.2%) on TTE. Eight cases with great vessel ¹⁸F-FDG uptake included disturbances of SVC, IVC, or PV inflow in 5 cases (62.5%), pericardial effusion in 3 cases (37.5%), and intracardiac mass in 3 cases (37.5%). FDG uptake confined to the great vessels was not found.