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Pet-scan Positive Mediastinal ? Met After RAI and Prior Nediastinal Operation

Last Updated: · Doctors


I would like your advice on the following case. A 28 year old female underwent total thyroidectomy and central neck dissection in 2004, for a classic papillary thyroid carcinoma (T2 (unifocal 2,5 cm), N1a, M0, EI). Afterwards she received 150 mCi radioiodine (under low iodine diet). The post dose scan showed uptake only in the thyroid bed. Antithyroglobulin antibodies were negative, but her thyroglobulin level at that time (off t4,) was 802 ng/ml. Several studies were performed, and a 18 FDG pet scan showed several foci of uptake in the mediastinum and both sides of the lateral neck (the latter were also shown on US). By then, about six months after the first surgery, offT4 her antibodies were again negative, andthe Tg was 540 ng/ml. Sheunderwent bilateral neckand mediastinum dissection,which was performed in an oncology center with a team of specialized thoracic and head and neck surgeons.The pathologist report confirmed metastatic lymph nodes for papillary thyroid cancer in all the three areas. After that, her thyroglobulin off T4 dropped to 120 ng/ml, and she was given additional 150 mCi radioiodine,with a negative post dose scan. Then, she was followed with neck sonograms, MRI, CAT scan (all of them negative) and thyroglobulin off T4 (her Ab were always negative) which gradually dropped to 64 and then 39 ng/ml over the next 18 months. No new doses of radioiodine were given, as we assumed her tumor was not radioiodine avid. Then thetg off T4rised agan, this time to 153 ng/ml, and a new 18-FDG- PET scanwithCAT was performed. It showed two small foci of 8,7 SUV: one in the upper right neck (near the mandible, maybe level II-I) and the other in the mediastinum. Despite the intensemetabolic activity, the size of the lesiones isabout 1,2-1,5 cm.The surgeons agree with theidea that surgery is the treatment of choice, but there is a concern of missing thelesions (mostly the mediastinal), since considerable scarring is expected, and therisk of complications is considered high (the previous surgeries werefortunately uneventful, besides a small neumothorax that evolved favourably).Is there anything you would recommend in this case? Thank you very much,

Ines Califano MD


A second mediastinal exploration is certainly depressing idea for all concerned. It makes sense to remove the lesion in the neck since you see it on US and it is PET positive. However neck nodes usually produce low levels of TG- such as 8-20. So presumably the lesion in the chest, or other lesions that may be present but unseen, is (are)likely to bethe source of the TG. You can not destroy a 1.5 cm thyroid metastasis with RAI when the uptake is so low that it is not seen on a post-therapy scan. However that scan was ?? a few years ago? If it was some time ago, I would consider doing another scan and then possible RAI treatment, on the remote and unlikely, (but hopeful) idea that significant uptake may be present, and there is nothing to loose except a bit of time. After that comes the idea of surgery and all of its possible problems, and the significant possibility that not all of the lesionspresent would be seen. But the patient has an increasing TG, Xray is of uncertain value, and she is not a candidate for chemo. In a certain sense, the second operation is the only real chance for a cure. So I would side with the surgeons if the patient is up to the procedure. Best regards,

Leslie J De Groot, MD