Keywords
carcinoma, papillary - cysts - thyroglossal cyst - neck
Introduction
The thyroid gland arises from the foramen cecum and descends in the neck to its final
resting place in the pre-tracheal space. An anomaly in this descent might leave space
in the tract, which leads to the formation of the thyroglossal duct cyst (TGDC). It
is estimated that around 7% of the adult population have a persistent duct, therefore,
leading to the formation of TGDC. This cyst is lined by squamous or pseudo stratified
ciliated columnar epithelium. The cyst might also contain some remnants of ectopic
thyroid gland, which is normally found in the cyst wall.
The TGDC tends to get infected and lead to swelling and discomfort in the anterior
neck. In the cases left untreated, recurrent infections can lead to sinus or fistula
formation. The definitive treatment for TGDC is surgery. Sistrunk operation is performed
to remove the TGDC and its tract.[1]
In very rare instances, the histopathology of the specimen reveals thyroid cancer,
particularly papillary thyroid carcinoma. There have been around 278 reported cases
of malignancy associated with TGDCs. We report two such cases of papillary thyroid
carcinoma arising from a TGDC.
Materials and Methods
A retrospective chart review was conducted at a tertiary care hospital from January
of 2004 to December of 2014. A total of 58 cases were identified with the diagnosis
TGDC that were subjected to Sistrunk operation. Out of the 58 cases, 2 were identified
that revealed papillary thyroid carcinoma on final histopathology of a sample from
the cyst. These cases were individually studied and are reported in this study along
with a review of the literature. Patients demographics, such as age, gender and comorbidities,
site of TGDC, type of carcinoma, type of surgery, postoperative radio-iodine ablation
and follow-up were noted.
Results
Case 1
A 38-year-old gentleman with no comorbidity presented with anterior neck swelling
for the past 5 years. Ultrasound examination of the neck revealed TGDC. The patient
had undergone excisional biopsy of the lesion at a tertiary care center, the result
of which showed papillary thyroid carcinoma; he, then, underwent formal Sistrunk procedure
along with total thyroidectomy without neck dissection. The final histopathology showed
no malignancy in the residual TGDC and, furthermore, no malignancy in the thyroid
gland. The patient has been on regular follow-up for the past 36 months and has remained
disease-free.
Case 2
A 45-year-old gentleman with a known case of hypertension presented with swelling
in the anterior neck that had been progressively increasing in size for the past 5
months. Ultrasound of the neck revealed TGDC. The patient underwent Sistrunk procedure,
and the final histopathology revealed papillary thyroid carcinoma along with normal
cyst wall. The patient further underwent total thyroidectomy and bilateral selective
neck dissection. The final histopathology revealed benign thyroid tissue; however,
level III of left revealed 2 nodes involved by the tumor. The patient subsequently
underwent radio-iodine ablation with 100 mcg. The patient has been on follow-up for
the past 6 years and has remained disease-free. Refer to [Table 1] and [Table 2].
Table 1
Patient demographics and presentation
|
Age
(year)
|
Gender
|
Comorbidity
|
Duration of symptoms
(months)
|
Presenting symptoms (neck swelling)
|
FNAC
|
Site of TGDC
|
|
Case 1
|
38
|
Male
|
None
|
60
|
Yes
|
No
|
Infrahyoid
|
|
Case 2
|
45
|
Male
|
HTN
|
5
|
Yes
|
No
|
Infrahyoid
|
Abbreviations: FNAC, fine needle aspiration cytology; HTN, hypertension; TGDC, thyroglossal
duct cyst.
Table 2
Treatment and follow-up
|
Type of surgery
|
Final histopathology
|
Total Thyroidectomy
|
Lymph node metastasis
|
Radio-iodine ablation
|
Follow-up
(Months)
|
Status at last follow-up
|
|
Case 1
|
Sistrunk procedure
|
PTC
|
Yes
|
NA
|
No
|
36
|
Alive, disease-free
|
|
Case 2
|
Sistrunk procedure
|
PTC
|
Yes
|
Yes
|
Yes
|
72
|
Alive, disease-free
|
Abbreviation: PTC, Papillary thyroid carcinoma.
Discussion
Thyroglossal duct cyst is the most common midline congenital anomaly of the neck.
It accounts for 70% of all congenital neck masses.[2] The TGDC has some normal thyroid tissue in 5–67% of all cases.[3] This thyroid tissue is normally located in the wall of the cyst and has a potential
to harbor malignancy.[3] The first case of carcinoma within the cyst was reported by Brentano in 1911.[4]
[5] The most common type of malignancy observed arising from within the cyst is the
papillary thyroid carcinoma.[3] Due to the rarity of such occurrence, this finding comes as a surprise to both the
patient and physician alike.[4]
The incidence of malignancy in the TGDC varies from study to study, and this large
variation is due to the small number of reported cases coupled with the total number
of cases studied of TGDC, which is required to calculate the incidence.[4] The incidence, however, is thought to be around 1.6%, as seen by in two large series.[6]
[7] In our case, we have 2 out of 58 cases under investigation showing papillary carcinoma,
which gives us an incidence of 3.4%.
The definitive treatment for the TGDC is the removal of the cyst along with some part
of the hyoid (body) and excision of the duct tract. Schlange, in 1893, first described
the surgical procedure as excision of the cyst and a part of the hyoid bone.[8] This procedure had a high recurrence rate. Walter Ellis Sistrunk, in 1920, described
a slightly more extensive procedure, which included cystectomy central hyoidectomy
(removal of body of hyoid) and tract excision up to the base of the tongue.[1]
[8] This had lower recurrence rate when compared with the first procedure and is considered
a gold standard for the treatment of TGDC to date.
Preoperative fine needle aspiration cytology (FNAC) is required to rule out malignancy,
which cannot be established until further evidence. S.Wei et al investigated 217 patients
with TGDC. Thirty-nine of the patients underwent FNAC, 37 (94.9%) of whom showed macrophages
and 2 who showed ectopic thyroid tissue.[3] The thyroid tissue is embedded within the fibrotic cyst wall, which is not easily
accessed, therefore, making FNAC an unreliable tool to diagnose a malignancy from
the TGDC.[3] None of the patients in this study underwent FNAC.
The pyramidal lobe is found in nearly half of the thyroid gland and can have attachment
with the hyoid bone via a fibrotic band.[3] The incidence of an isolated focus of papillary thyroid cancer in the pyramidal
lobe is very low, approximately 0.4%.[9] Metastasis of papillary carcinoma to lymph nodes tend to form cysts.[3]
[10] The pyramidal lobe of thyroid and the Delphian node are both found in the midline;
therefore, it is important to differentiate papillary thyroid carcinoma arising from
the duct cyst from the other two.[3] Given the two conditions, papillary thyroid carcinoma arising from the pyramidal
lobe or from the Delphian node cyst can be confused with TGDC carcinoma if not examined
carefully.[3] In our study, in both of these patients normal thyroid tissue along with thyroglossal
duct remnants were identified.
Due to the indolent course of papillary thyroid carcinoma and its ability to arise
from ectopic thyroid tissue independent of the thyroid gland, a formal Sistrunk procedure
without total thyroidectomy can suffice in the low-risk group.[4] For clinically suspicious cases, radiological examination and FNAC of the thyroid
nodule can suggest further treatment.[4] In our study, both patients underwent total thyroidectomy, with case 2 also undergoing
bilateral selective neck dissection due to suspicious nodes on radiological examination.
On histopathology, neither patient had evidence of malignancy in the thyroid gland,
but case 2 had two nodes positive for tumor metastasis to left level III. Cervical
nodal metastasis has been reported from 10–15% in such cases;[4] however, in our study it represented 50% (case 2) of our sample, but that cannot
be generalized based on two cases.
Extensive investigation for a disease that can be diagnosed clinically is not warranted,
especially given the low incidence of malignancy associated TGDC, but high-risk patients
aged > 45 years with clinical suspicion can be referred to FNAC and ultrasound of
neck.
Conclusion
We report 2 cases of papillary thyroid carcinoma arising from a TGDC from 58 cases
under review. Both patients underwent Sistrunk operation and total thyroidectomy.
Both patients are stable and disease-free since the time of surgery up until the last
follow-up. We suggest further investigation and thyroidectomy with or without neck
dissection in the high-risk group.
