Isolated Cardiac Metastasis From Papillary Thyroid Cancer: Prolonged Survival with Late Diagnosis Related to Inadequate Positron Emission Tomography Preparation

Dear Editor:

We read with interest the recent review of cardiac metastases from thyroid carcinoma in Thyroid (1). As discussed, survival data are infrequently reported and the natural history of the metastases is unclear. Cardiac metastases are usually an incidental finding at autopsy or are discovered when the patient develops cardiac symptoms, heralding a brief survival with a mean of about 13 weeks. Cardiac metastases from papillary thyroid carcinoma (PTC) are very rare; in most cases they result from direct extension from the major blood vessels of the neck (2,3). They are also discovered principally in patients with widespread systemic tumor dissemination (4). We report here a unique case of isolated cardiac metastasis from PTC, which allowed us to follow the natural history of this condition. In our patient it was, in fact, of relatively long duration.

A 54-year-old woman presented with locally aggressive PTC of the tall cell variant. It involved both lobes of the thyroid with capsular, small vessel, and lymphatic invasion. A total thyroidectomy followed by external beam radiation was performed in June 2005. Serum thyroglobulin (Tg) was 2 ng/mL or less until June 2007, and she was considered disease free. In December 2007, her serum Tg was found to have increased to 15 ng/mL (see Supplementary Fig. S1; Supplementary Data are available online at www.liebertonline.com/thy). In February 2008 recombinant human thyrotropin (rhTSH) as Thyrogen^® (Genzyme Corporation, Cambridge, MA) was administered, with the serum Tg increasing to 58.7 ng/mL. Radiologic studies in early 2008, including neck ultrasound, positron emission tomography (PET)/computed tomography (CT) scan, bone scan, and magnetic resonance imaging (MRI) of the head were negative; however, Tg levels on levothyroxine (LT₄) suppressive therapy continued to rise, reaching 260 ng/mL in May 2009. Repeat radiologic studies at that time were again negative. A marked increase in serum Tg to 704 ng/mL was noted in December 2009, prompting restaging while on continued LT₄ therapy. Thyroid ultrasound and CT scan of the chest were again negative. PET/CT scan (see Supplementary Fig. S2), however, showed a large intense focus of fluorodeoxyglucose (¹⁸FDG) uptake in the region of the right atrium. In retrospect, this abnormal area was also present, albeit less ¹⁸FDG avid, in December 2008 and June 2009. In view of concomitant intense left ventricular myocardial FDG uptake, it was interpreted as a physiologic focal activity in the atrial appendage. However, the PET scan from December 2009 performed under a more stringent low carbohydrate diet revealed a clearly abnormal enlarging lesion (see Supplementary Fig. S2).

A dedicated cardiac MRI showed a sessile mass at the superior vena cava and right atrial junction. Using cardiopulmonary bypass the lesion was removed in February 2010 without any complications such as arrhythmias. Histopathology of the lesion revealed PTC identical to the primary tumor infiltrating the cardiac muscle (see Supplementary Figs. S3–S5). The postoperative course remained uneventful; 3 months after surgery the serum Tg was 2.1 ng/mL.

A unique aspect of our patient was the presence of isolated cardiac muscle metastases without evidence of either local angio-invasion, disseminated disease, or a tumor thrombus. To the best of our knowledge this has not been reported in patients unless they had widespread dissemination of their thyroid cancer.

The fact that the diagnosis eluded us for 2 years emphasizes the importance of proper patient preparation for ¹⁸FDG PET/CT. Because the patient was not compliant with the low carbohydrate diet, intense myocardial ¹⁸FDG uptake occurred, which obscured the lesion in the initial PET scans. In the subsequent PET/CT scan in December 2009, the patient was adequately prepared so the ventricular myocardial uptake was reduced, thus facilitating the detection of the abnormal atrial activity.

Almost 2 years after cardiac surgery the patient remains asymptomatic, although she developed an isolated pulmonary metastasis in August 2011; this was treated with stereotactic radiotherapy. We believe that if the cardiac metastasis had not been resected she would have developed life-threatening cardiac symptoms. In retrospect, our failure to detect the cardiac metastasis at an early stage gave us the opportunity to observe a natural history of cardiac metastases of relatively long duration. As our patient illustrates, a rising serum Tg in an asymptomatic patient with thyroid cancer should lead to an aggressive and careful radiologic investigation. This may lead to detection of resectable metastasis which, if left untreated, would be likely to cause major complications.