I would like your opinion regarding a 63 year old lady with well differentiated follicular variant papillary carcinoma (3.7cm) with mediastinal metastases.
She presented in August 2005 with thyrotoxicosis (TSH <0.04, FT3 6.3, normal FT4) and subsequent tests demonstrated a dominant left thyroid nodule (3 cm) and nondominant nodule in the right lobe (<3mm) with increased tracer uptake in the left hemi-thyroid. Anti-TP0 were present in low titers at 81 IU/ml ( 0-60). As needle cytology of the left nodule favoured oncocytic proliferation she had left hemi-thyroidectomy in September. Unfortunately, the pathology revealed a 37mm well differentiated thyroid carcinoma displaying mixed follicular and papillary features, with focal full thickness capsular penetration. A completion thyroidectomy was performed in early December with no evidence of residual malignancy in the right thyroid lobe.
She received ablative RAI (3.55GBq of Iodine-131 orally) 7 weeks after completion thyroidectomy, however, the TSH on the day of dosing was sub therapeutic (21.9 mIU/L). Thyroglobulin was <0.02ug/l and thyroglobulin antibody was <40 kIU/L. Whole body survey, 3 days after the RAI dose showed a focal moderately intense abnormal radioiodine accumulation in the anterior mediastinum in the midline just below the transaxial level of the carina. When correlated with the low-dose CT scan, this appeared to correspond to a small soft tissue mass in the anterior mediastinum. There was no definite evidence of iodine avid thyroid tissue in the region of thyroid bed or elsewhere. She was started on levothyroxine after RAI.
How do I best manage this patient?
- Repeat diagnostic scan in 6 months and consider second RAI treatment if positive diagnostic scan?
- Consider thoracotomy for removal of metastases if positive diagnostic scan as mediastinal nodes/metastates may not ablate with RAI therapy?
- Monitor thyroglobulins / surveillance neck ultrasound/ CT scan chest for recurrent disease whilst maintaining TSH suppressive therapy ( 0.1- 0.4), if diagnostic scan in 6 months is negative?
- Should Radiotherapy be considered? Any other recommendations?
Thank you in advance for your advice.
K. Guttikonda FRACP, NSW Australia
In summary this is a patient with uptake in the anterior mediastinum corresponding to a small mass at CT scan with an undetectable thyroglobulin and negative anti-Tg while TSH was elevated. The Tg result may be interpreted as false negative, which is possible in case of small lymph node metastases. As an alternative, one can think of unspecific uptale of radioiodine in a non-thyroidal mass (i.e. thymus, or something else) which has rarely been described in that area of the mediastinum. I would perform a stimulation of serum Tg using rhTSH and CT scan (and/or FDG-PET) in six months. In case of negative Tg and FDG-PET, even if the mediastical mass is still visible at CT, I would not recommend therapy but only follow-up. In case of evolution at CT or positive PET and/or stimulated Tg I would recommend RAI therapy followed by post-therapy WBS. No need in my opinion for a diagnostic RAI WBS.
F. Pacini MD