Abstract
Differentiated thyroid carcinoma (DTC), arising from thyroid follicular epithelial cells, accounts for the vast majority of thyroid cancers. Despite being well-differentiated, papillary thyroid cancers may be overtly or minimally invasive. They may invade lymphatics but are less likely to invade blood vessels. Iodine-131 (131I) is routinely used to image patients after thyroidectomy to assess the presence of residual thyroid tissue with or without metastasis. False positive 131I scans, showing the presence of 131I uptake in the absence of residual thyroid tissue or metastases can occur, although they are uncommon. Unless recognized as a false positive, 131I uptake may result in diagnostic error and lead to administration of an unnecessary higher therapeutic dose. We present a 55 year old female, histopathologically proven case of follicular variant of papillary carcinoma that underwent Total Thyroidectomy. Residual thyroid and whole body scan showed moderate residual thyroid tissue with abnormal 131I in right lung masquerading as right lung metastases. SPECTCT (single photon emission computed tomography – computed tomography) was incremental in localizing the site of 131I uptake to bronchiectatic changes. 131I diagnostic and post therapy scans are useful to risk stratify DTC patients’ so that amount of high dose 131I to be administered to patient can be estimated and judiciously used in their treatment.
Highlights
55 year old female, histopathologically proven case of follicular variant of papillary carcinoma underwent Total Thyroidectomy
SPECT CT was performed which localized the site of abnormal 131I uptake to cystic bronchiectatic changes in right lung
SPECTCT of thorax was incremental in localizing the 131I uptake to bronchiectatic changes to right lung
Summary
55 year old female, histopathologically proven case of follicular variant of papillary carcinoma underwent Total Thyroidectomy. Residual thyroid and whole body 131I scan was performed three weeks after the sugery. Whole body and static anterior neck images showed moderate residual thyroid tissue with abnormal 131I in right lung mimicking metastases (Figure 1). SPECT CT was performed which localized the site of abnormal 131I uptake to cystic bronchiectatic changes in right lung. SPECTCT of thorax was incremental in localizing the 131I uptake to bronchiectatic changes to right lung. Post therapy 131I scan performed (Figure 2) on day 5 revealed significant 131I uptake in thyroid bed as expected in a post therapy setting. SPECTCT of thorax in post therapy setting was performed which showed corresponding cystic bronchiectatic changes in bilateral lungs suggesting new left lung infection or inflammation. A radioiodine scan showing abnormal uptake outside the thyroid bed must be studied carefully and alternative reasons for the finding must be considered. The prognosis of PTC and follicular thyroid cancer are almost similar
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