We present a case of a six year old boy with an enlarging thyroid mass. He was asymptomatic, euthyroid and had no family history of thyroid disease.
Examination and neck ultrasound showed hard mass replacing left thyroid lobe with no lymphadenopathy. FNA cytology suggested diagnosis of lymphoepithelial cyst of the thyroid.
Left hemithyroidectomy and isthmusectomy was performed. At operation no lymphadenopathy was seen and right thyroid lobe was normal. Mass did not infiltrate muscles or trachea.
His recovery was uneventful with no perioperative complications.
Specimen measured 60×25×25 mm and weighted 22 grams. Gross examination showed encapsulated, grey brown mass, which on cut section had a homogenous grey white appearance with a single mucin filled cystic space.
Histology showed a highly cellular tumour with spindle cell and glandular components forming a biphasic pattern. Mitotic figures were rare (4/10 HPF). The glandular component consisted of epithelial (columnar and squamous) lined cystic spaces with no histological atypia.
Immunocytochemistry showed that both components stained positively CK5 and bcl 2. The glandular component was positive for cytokeratins (AE1/3) and epithelial membrane antigen. The spindle cell component stained with smooth muscle actin, vimentin, CK14. Thyroglobulin and calcitonin staining were negative throughout.
Thyroid masses arising from intrathyroidal remnant of branchial pouch derivative are very rare. Only 16 cases of Lymphoepithelial Thyroid Cysts (LETC) and 20 cases of SETTLE tumours were reported in English literature. LETC are benign lesions associated with thyroiditis while SETTLE tumours retain the potential to differentiate along thymic line and have malignant potential. Early surgical excision and histological confirmation is the recommended treatment.