MON-403 - A Case of Thyroid Carcinoma in Thyroglossal Duct Cyst- A Rare Entity

Introduction
Thyroglossal duct cyst is the most common congenital neck abnormality present in 7%
of the population. It results from the incomplete obliteration of thyroglossal duct during
embryonic development. It typically presents as a painless midline neck mass. The cyst
may contain viable thyroid tissue and fluctuates in size and can become infected.
Papillary thyroid carcinoma, the most common type of thyroid cancer, accounts for 84-
90% of all thyroid cancers, and can also be associated with thyroglossal duct cysts.

Case
We present the case of a 17-year-old female who presented to the endocrine clinic for
surveillance and management post thyroglossal duct cyst excision. The patient reported
that at age 12 she had her first episode of neck pain and tender right neck swelling
during an acute infection. She continued to have similar episodes when she had upper
respiratory tract infections. She was evaluated by an Otorhinolaryngologist. Imaging
revealed a 3cm cystic mass to the right of the midline in the strap muscles and a 0.5cm
hypoechoic nodule in the thyroid isthmus and 0.2cm hypoechoic nodule in the right
thyroid lobe. The patient underwent thyroglossal duct cyst removal (Sistrunk procedure).
Post operative pathology showed an incidental finding of three foci of papillary thyroid
microcarcinoma, follicular variant. Thyroid ultrasound was unremarkable. Thyroid
function tests were normal (TSH 0.835 uIU/ml (normal= 0.500-3.400), FT4 0.9 ng/dl
(normal =0.8-2.0) and TotalT3 166 pg/ml (normal =115-195)).
Two years after the surgery, the patient reported doing well and was not taking thyroid
or other medications. Her most recent thyroid labs showed TSH 1.178 uIU/ml (normal
0.550-4.780), FT4 0.95 ng/dl (normal 0.89-1.76) and FT3 2.79 pg/ml (normal 2.30-4.20),
normal thyroid peroxidase antibodies 37 U/ml (normal 0-60) and thyroglobulin
antibodies 18U/ml (normal 0-50). Thyroid ultrasound showed 2 sub-centimeter
hypoechoic benign appearing nodules.

Discussion
Our case highlights that although rare, malignancy may be detected in thyroglossal duct
cysts. Reports suggest that it is found in 1%-7% of cases. Most thyroglossal duct cyst
carcinomas are diagnosed postoperatively on pathology, making histologic examination
essential. Concomitant cancer in the thyroid gland is present in 35-62% of cases, which
is a major concern, although papillary thyroid carcinoma, the most common histologic
type, has an excellent prognosis. It necessitates thorough evaluation of the thyroid
gland, and patients may have to undergo total thyroidectomy, if malignancy is found.
Late recurrences can also occur requiring regular thyroid gland surveillance with
ultrasound and lab monitoring.

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