A hydatid cyst may rarely be found in thyroid gland. It may not be considered in the differential diagnosis of a thyroid cyst.
Features of the thyroid cyst:
(1) progressively growing
(2) usually solitary
(3) cold on scintigraphy
(4) may be asymptomatic or large enough to cause symptoms (dysphagia, respiratory distress)
Reasons to suspect:
(1) The patient has lived in or visited a region endemic for hydatid disease.
(2) The patient has a hydatid cyst elsewhere (liver, lung, etc).
(3) The patient has a positive ELISA test for anti-hydatid antibodies.
(4) Identification of germinal vesicles on imaging study (ultrasonography, CT, MRI).
(5) The patient has eosinophilia.
Aspiration of the cyst is contraindicated because of the risk of anaphylaxis and iatrogenic spread.
The cyst should be totally excised, preferrably intact.
Chemotherapy (mebendazole, praziquantel) following surgery can help to prevent recurrence.
