METHODS
Preoperative diagnosis of a hydatid cyst of thyroid origin can be challenging, as they can mimic tumors, abscesses, and other space-occupying thyroid lesions such as thyroglossal cysts and branchial cleft cysts (4) (9).
Complete blood count(CBC), thyroid function test, renal function test, blood sugar, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) were within normal limits. Ultrasonography (USG) of neck revealed a large multiloculated heterogeneous, anechoic lesion measuring 8.1 cm x 4 cm x 5 cm in left thyroid lobe and was designated a TI-RADS (Thyroid Imaging Reporting and Data System) -3 lesion[Figure 1 ]. The other lobe and lymph nodes were normal. With a differential of thyroid nodule, Fine needle aspiration cytology (FNAC) was performed which yielded 18 ml of granular to clear watery fluid. Post FNAC period was uneventful. Cytocentrifuged Giemsa stained and unstained smears showed multiple protoscolices having rostellum containing rows of refractile hooklets[Figure 2 ]. Numerous free hooklets, fragmented laminated membranes of ectocyst and germinative layer were identified. Refractile hooklets had claw-like appearances with pointed one end and bifid another end[Figure 2 ]. Enzyme-Linked Immunosorbent Assay (ELISA) was positive for Echinococcus with serum IgG levels of 13 Net Titers Units (NTU). Detailed computed tomography (CT) scan showed lesions that were limited to the thyroid. On detailed questioning, the patient gave no past history of hydatid cyst disease or similar symptoms in family members. A final diagnosis of the primary hydatid cyst of the thyroid was made.