INTRODUCTION
[sup]18[/sup]F-FDG PET-CT has an active role in staging of metastatic melanoma. Although intra-cardiac metastases of melanoma are relatively uncommon, a careful observation of cardiac FDG-uptake is required if there are new signs and symptoms of cardiac arrhythmia. Cardiac muscle has intrinsic high FDG-uptake, hence it is often difficult to visualize abnormal foci of FDG-uptake. Contrast-enhanced CT of the heart may further assist in visualizing the location of abnormal intra-cardiac lesions.
CASE REPORT
A 52-year-old man was referred for an FDG-PET-CT-scan with clinical suspicion of parotid malignancy, and with recent onset atrial fibrillation. The scan demonstrated extensive metastatic disease including cervical and retroperitoneal lymphadenopathy, lung, renal, adrenal, bone and subcutaneous metastases ([fig:5001]Figure 1a[/fig]). In particular, there was a 57 mm focus of intense FDG uptake (SUVmax 23.9) seen within the right atrium suggestive of intra-cardiac metastatic disease ([fig:5001]Figure 1b[/fig] arrows, at two axial levels within the heart). This may explain the new onset of atrial fibrillation. Cervical nodal biopsy confirmed metastatic melanoma. Echocardiogram confirmed a lesion in the right atrium (not shown). The patient was then given a course of oral Vemurafenib 960 mg once a day, a standard treatment for metastatic melanoma. The patient had mixed response to therapy. Overall there was decrease in the FDG avid disease burden and in the intensity of the uptake in previously detected lesions. However, there were a few new skeletal lesions compared to the pre-treatment scan ([fig:5001]Figure 1e[/fig]). After the treatment, the right atrial mass reduced in maximum size by 28% (41 mm), and FDG-uptake reduced by 60% (SUVmax 9.6) ([fig:5001]Figure 1c[/fig] arrow, at the same two axial levels as [fig:5001]Figure1b[/fig]). Contrast-enhanced CT demonstrated residual atrial disease ([fig:5001]Figure 1d[/fig] arrow). The symptom of atrial fibrillation spontaneously resolved.
Literature Review and Discussion
Most malignant melanoma subtypes are known to be FDG-avid (1,2), hence 18F-FDG PET-CT has been commonly used in the management of malignant melanoma, in particular, for staging and monitoring response to therapy (3).Cardiac metastases of melanoma are relatively uncommon (4,5), but when it occurs it often manifests with cardiac signs such as cardiac arrhythmia and cardiac failure (4,6). Other signs and symptoms of cardiac metastases include ventricular inflow obstruction, embolism, valvular heart disease, syncope and pericardial effusion (7). Atrial fibrillation usually accompanies right atrium metastases (8,9).Primary FDG-avid cardiac tumors are rare, and histologically over three-quarters of primary heart tumors turn out to be benign, almost half of them being myxomas (7).Other common malignancies that present with cardiac metastases are carcinoma of the lung, breast, oesophagus, lymphoma and leukaemia (7).Although stage 4 metastatic melanoma is rarely curable, a few new approaches have shown clinical benefit by prolonging overall survival in randomized trials (10). Current treatment regimes of stage 4 melanoma include chemotherapy and immunotherapy (11). One of the most promising treatment options is oral Vemurafenib, a standard treatment for metastatic melanoma (12). Vemurafenib plays a role by inhibiting the mitogen-activated protein (MAP) kinase pathway in patients whose tumors have a V600 mutation in the BRAF gene (13,14,15,16).Our patient was given oral Vemurafenib 960 mg once a day, and the cardiac lesion demonstrated partial response to therapy. The cardiac lesion has reduced in size and FDG-avidity, and the symptom of atrial fibrillation has resolved appropriately (17).As the cardiac muscle demonstrates normal physiological FDG-uptake, it is often hard to visualize/localize a possible intra-cardiac metastatic focus. Contrast-enhanced CT or echocardiography may assist identifying such lesions by delineating the cardiac mural surface, as shown in our case (18).