DISCUSSION
The first reported case of thyroid involvement with hydatid cyst was in
1946 (4). Since then, there have been reports from the endemic regions,
however to our knowledge, none have been reported from South Asia.
Hydatid cyst of thyroid can develop either primarily (affecting only the
thyroid) or secondarily (involving multiple organs). Possible
pathogenesis is emergence of oncosphere larvae in gastrointestinal tract
followed by passage to systemic circulation either after bypassing the
liver or passing through liver and reaching to thyroid gland (5).
Humans are accidental hosts and contract the disease by accidentally
ingesting contaminated food and water or through contact with a
definitive host (10). In our case, the patient had a history of exposure
to cattle and sheep similar to that in previous cases.
Symptoms of hydatid cyst in thyroid depends upon size and adherence of
the lesion to surrounding structures with most of the patients are
asymptomatic except for non-progressive swelling as ours The slow
growing pattern explains clinical dormancy for several
years(11). However, patients may complaint of difficulty
breathing, swallowing, hoarseness , anaphylaxis, pyogenic abscess
formation and cystotracheal fistula secondary to erosion of tracheal
wall by cyst wall (4).
USG is a routine investigation to visualize cyst and daughter vesicles.
CT /MRI are used to assess the location of cyst in relation to its
surrounding structures (4).
Despite having limited sensitivity and specificity in primary thyroid
hydatid cyst disease, immunological methods like indirect
hemagglutination, latex agglutination, ELISA, and immune
electrophoresis are important modality if diagnosis remains unclear
(12).
The role of FNAC in preoperative diagnosis of thyroidal hydatid cyst is
controversial despite higher sensitivity and specificity pertaining to
the high risk of anaphylactic reactions and the dissemination of cystic
elements leading to inflammation making surgery difficult (4).
However, our patient didn’t have immediate or late reactions following
the USG guided FNAC.
Ultrasound scan of the neck was performed in our patient which was
non-conclusive and FNAC findings revealed diagnosis of hydatid cyst of
thyroid to detect the unilateral hydatid cyst on the left side of
thyroid gland. To the best of our knowledge, there has been only a case
of thyroid hydatid cyst diagnosed by FNAC before the surgery as in our
case (6).
Although post-surgical histopathology remains gold standard, an
integrative approach including patient history, place of origin,
examination, imaging examinations like USG, CT scan, magnetic resonance
imaging (MRI), scintigraphy, serological examination and FNAC (4).
Surgical resection is the preferred treatment option. Administering
anti-parasitic drugs like Mebendazole or Albendazole may be alternative
treatment when there is a contraindication for surgery and as
postsurgical adjuvant chemotherapy for preventing recurrence. Follow-up
is recommended after 3 months, 6 months and after a year of surgical
operation (5)(7). The patient’s condition significantly improved
following her surgical operation, and no antiparasitic medications were
needed as there were no complications after
surgery.