Malignant Ectopic Thyroid Tissue with Distant Metastasis-A Case Report.

BACKGROUND: Ectopic Thyroid Tissue is the most common form of thyroid dysgenesis. But primary malignant transformation in ectopic thyroid tissue is quite a rare entity, with follicular malignancy being the dominant form at ectopic sites. Very infrequently, malignant ectopic thyroid tissue can present with metastasis to lymph nodes. But we report a case of malignant ectopic thyroid tissue over manubrium sterni with distant metastasis. CASE REPORT: A 42-year-old Pakistani female presented to us in Endocrine clinic with gradually increasing swelling on anterior aspect of manubrium sterni for last 6 months. She had no goitre & was clinically and biochemically euthyroid. Rest of systemic exam was also unremarkable. CT chest showed a circumscribed soft tissue density mass arising from sternum, measuring 3.9 x 3.9cm, causing erosions of anterior, right lateral & posterior walls of sternum. Trucut biopsy of the sternal mass proved it to be thyroid tissue with follicular differentiation and occasional mitotic figures. Multiple nodules were also noted in Thyroid gland in US Neck. She underwent total Thyroidectomy & excision of ectopic thyroid tissue over manubrium sterni. Extensive histopathological examination of primary thyroid gland showed benign nodular hyperplasia with no evidence of malignancy. Ectopic thyroid tissue showed minimally invasive follicular thyroid carcinoma with tumor size of 3.2 x 2.3cm. Her postoperative 21-day biochemical profile showed TSH 22.345 µIU/ml (0.4 to 4.2), Serum Thyroglobulin 88.3ng/ml, Anti-TG antibodies <20.0IU/ml. Based on the histopatholigical diagnosis, she went through 30mCi RAI131 ablation. The post-ablative whole body scan showed good uptake of ablative dose over thyroid bed and evidence of multiple well-defined rounded areas of abnormally increased tracer accumulation over mid and lower dorsal spine, lumbar region and right iliac bone, representing bone metastasis. It was followed by MRI spine which showed foci of metastatic deposits in T1-T3 and L2 vertebral bodies & abnormal signals showing post-contrast enhancement in superior mediastinum with invasion of medial ends of both clavicles, more marked on right side. So patient was found to have malignant ectopic thyroid tissue with distant bone metastasis. CONCLUSION: To the best of our knowledge, we describe the first case of its kind having malignant ectopic thyroid with metastasis to spine & ilium. Such cases appear difficult to manage and may impose difficulties in making their treatment decisions. [ABSTRACT FROM AUTHOR]