|Year : 2015 | Volume
| Issue : 3 | Page : 119-123
Developmental anomalies of thyroid: Thyroglossal duct cyst associated with ectopic thyroid: Radiology and nuclear medicine imaging findings
Sunita Nitin Sonavane1, Mangala Targe Munde2, Biju Menon3, Ramesh Asopa3
1 Department of Nuclear Medicine and PET/CT, Radiation Medicine Center, Parel, Mumbai, Maharashtra, India
2 Department of Radiology, Tata Memorial Hospital, Mumbai, Maharashtra, India
3 Department of Nuclear Medicine, Radiation Medicine Center, Parel, Mumbai, Maharashtra, India
|Date of Web Publication||16-Oct-2015|
Dr. Sunita Nitin Sonavane
Radiation Medicine Centre, Bhabha Atomic Research Center, C/o Tata Memorial Center Annex, Parel, Mumbai - 400 012, Maharastra
Source of Support: None, Conflict of Interest: None
We report a case of euthyroid young female with anterior midline neck swelling, non-tender gradually increased to present size since childhood. On anatomic cross sectional imaging ultrasonography (USG) and computed tomography (CT) scan showed multiseptated cyst in the midline neck, infrahyoid region with absent thyroid gland in its normal location suggestive of TGDC with absent normal thyroid gland. Thyroid scintigraphy study detects functioning thyroid tissue within the thyroglossal cyst and patent thyroglossal duct. F18-FDG PET/CT showed no uptake within the thyroglossal cyst and patent thyroglossal duct indicating no evidence of malignancy. This case highlights the role of nuclear medicine as a diagnostic challenging modality and thus aiding in therapeutic decision.
Keywords: Computed tomography, pertechnetate, positron emission tomography, radioiodine, thyroglossal duct cyst, ultrasonography
|How to cite this article:|
Sonavane SN, Munde MT, Menon B, Asopa R. Developmental anomalies of thyroid: Thyroglossal duct cyst associated with ectopic thyroid: Radiology and nuclear medicine imaging findings. Thyroid Res Pract 2015;12:119-23
|How to cite this URL:|
Sonavane SN, Munde MT, Menon B, Asopa R. Developmental anomalies of thyroid: Thyroglossal duct cyst associated with ectopic thyroid: Radiology and nuclear medicine imaging findings. Thyroid Res Pract [serial online] 2015 [cited 2019 Jul 20];12:119-23. Available from: http://www.thetrp.net/text.asp?2015/12/3/119/157938
| Introduction|| |
The most common congenital neck mass is the thyroglossal duct cyst (TGDC), accounting for 70% of all congenital neck anomalies  They generally occur in young patients and are caused by a defect in thyroglossal duct closure.  TGDC is typically located in the midline of the neck adjacent to the hyoid bone, although they can occur anywhere along the course of the thyroglossal tract.  Most common association is the ectopic thyroid. TGDCs are epithelial lined cysts. Over half of these cysts have normal thyroid follicular tissue in their walls. Malignant lesions are rare in TGDCs (about 1%) and most of them develop from ectopic thyroid remnants. 
Developmental abnormalities of the thyroid gland includes three major groups as (1) agenesis of thyroid gland, which is an important cause of neonatal hypothyroidism; (2) dysgenesis of the thyroid which includes ectopic thyroid, hemiagenesis of thyroid; (3) abnormalities due to persistence of the thyroglossal duct.  TGDC (TGDC) is the most common congenital abnormality of thyroid development.  The cyst is located at the level of hyoid bone (15-50%), infrahyoid (25-65%), or in suprahyoid location (20-25%). 
| Case Report|| |
A 19-year-old female was presented with complain of anterior midline neck swelling. The swelling was first noticed at the age of 2 years which gradually increased to the present size. There was no complaint of pain or difficulty in swallowing. The patient was asymptomatic. The menstrual history was normal with regular menstrual cycles. On clinical examination, there was rounded swelling noted in anterior midline location in the neck [Figure 1]. It was cystic, non-tender, mobile, not attached to overlying skin and skin over the swelling was normal. The swelling moved with swallowing and classically elevates on tongue protrusion. There was no palpable cervical lymphadenopathy.
Patient was further evaluated, thyroid function tests was done (T4 = 7.5 μg/dl normal, FT4 = 1.1 ng/dl normal, TSH = 7.9 μIU/ml mildly elevated, AMA = negative). Thyroid function test revealed subclinical hypothyroid status. Ultrasonography (USG) revealed a thin walled multiseptated anechoic cystic lesion measuring appro × 3.7 × 1.7 cm anterior to trachea in the midline in the neck more on right side. Both the lobes of thyroid gland and isthmus was not visualized in the thyroid fossa [Figure 2].
|Figure 2: Ultrasonography revealed a thin walled multiseptated anechoic cystic lesion measuring approx 3.7 × 1.7 cm anterior to trachea in the midline of neck, more on right side. Both the lobes of thyroid gland and isthmus was not visualized in the thyroid fossa |
Figure 1: Patients Neck Photo- A Ant View, B Left Lateral View
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For further characterization of lesion, its extent plain and contrast enhanced CT neck was performed. Plain CT scan revealed absent normal thyroid gland in its normal site in the thyroid fossa [[Figure 3] and [Figure 4] left column]. A large well-defined lobulated cystic lesion (24-28 HU) with hyperdense peripheral wall, multiple thin septae was noted in the midline anterior neck space, anterior to the trachea. Few hyperdense thick septae and soft tissue was noted on inferior lateral aspect of cyst. The lesion was extended from below the hyoid bone to the sternal notch (thoracic inlet). No evidence of calcification. Bilateral sternocleidomastoid muscles were displaced laterally. The lesion measures 3.6 × 2.3 × 6.2 cm (Transverse × Anteroposterior × Craniocaudal dimensions). Small hyperdense soft tissue focus was noted just anterior to hyoid bone. On post contrast CT [Figure 5], there was moderate enhancement of peripheral wall and septae of the cyst. Thick enhancing septa/soft tissue on lateral aspect of cyst were noted suspecting ectopic thyroid tissue or carcinoma. Also intense enhancement of hyperdense soft tissue focus anterior to hyoid bone was noted suggestive of ectopic thyroid tissue. There is no obvious destruction/invasion of thyroid or cricoid cartilage seen. No abnormal cervical lymph nodes were noted.
|Figure 3: UPPER ROW-Maximum Intensity Projection (MIP) of regional neck FDG PET. Left image anterior and right image left lateral view show no abnormal focal FDG uptake in region of neck. MIDDLE ROW coronal image left CT noncontrast and right fused FDG PET/ CT. LOWER ROW sagittal image left CT noncontrast and right fused FDG PET/CT|
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|Figure 4: Left column noncontrast CT and right fused PET/CT transaxial images. Noncontrast CT scan revealed absent normal thyroid gland, large 3.6 × 2.3 × 6.2 cm well defined lobulated hypodense infrahyoid cystic lesion with hyperdense peripheral wall and midline thin multiple septae reaching to the sternal notch (thoracic inlet). 18F-FDG regional neck PET/CT revealed no definite FDG uptake in the TGDC or elsewhere in the neck to suggest malignancy|
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|Figure 5: Post contrast CT, there was mild rim enhancement of cystic lesion with multiple septae. Strong enhancement of thick wall/soft tissue on lateral aspect of cyst and soft tissue focus anterior to hyoid bone suggestive of ectopic thyroid tissue|
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As the normal thyroid gland was absent, to look for ectopic thyroid tissue patient was further evaluated with 99mTechnetium pertechnetate thyroid scan was performed by intravenously injecting the 4.2 mCi 99mTc pertechnetate and images of thyroid were obtained in multiple projections. The study showed tracer uptake in front of hyoid bone and extended below as rounded to the suprasternal notch suggestive of functional ectopic thyroid tissue anterior to hyoid and also within the TGDC. Normal thyroid gland was absent. No evidence of tracer uptake elsewhere in the chest or other site [Figure 6].
|Figure 6: 99m-Technetium pertechnetate thyroid scan anterior neck static view showed tracer uptake in front of hyoid bone and extended below as rounded to the suprasternal notch suggestive of functional ectopic thyroid tissue anterior to hyoid and also within the TGDC. Normal thyroid gland was absent. No evidence of tracer uptake elsewhere in the chest or other site|
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To study organification function 131I scan was done at 24 hours after patient was taken 25 micro Curie capsule orally. Images were obtained at 2 hours and 24 hours uptake. One hundred and thirty one scan showed absent normal thyroid gland in the normal location thyroid fossa. Tracer uptake was noted anterior to hyoid bone suggestive of ectopic thyroid tissue. Tracer uptake was also noted extend from hyoid bone below as linear track to rounded area inferiorly upto the suprasternal notch. This represents functioning thyroid tissue in the TGDC. The 2 and 24 hours uptake was 7.88% and 22.7% respectively [Figure 7].
|Figure 7: 131-Iodine scan showed absent normal thyroid gland in the thyroid fossa. Abnormal tracer uptake was noted anterior to hyoid bone suggestive of ectopic thyroid tissue, extending below hyoid bone as linear track to rounded area inferiorly upto the suprasternal notch representing functioning thyroid tissue in the TGDC|
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As there is risk of malignancy (approx 1%) of carcinoma in TGDC containing ectopic thyroid tissue, 18F-FDG PET/CT was suggested [Figure 3] and [Figure 4]. Regional PET/CT was done 60 minutes after intravenous injection of 2.5 mCi of 18F-FDG using whole body full ring dedicated LYSO PETCT time of flight scanner. Attenuation correction was done by low dose CT. The study revealed no definite FDG uptake in the TGDC or elsewhere in the neck to suggest malignancy.
Thus, TGDC was containing the only functioning ectopic thyroid tissue within it and also anterior to hyoid bone with absent normal thyroid gland in thyroid fossa. Both anatomical and functional imaging modalities were required for complete evaluation TGDC, a developmental anomaly of thyroid gland.
| Discussion|| |
The thyroid gland develops from the foregut in the first trimester of pregnancy, beginning around the fifth week of gestation and completed by the tenth week of gestation. During fetal development, the thyroid gland descend from its place of origin, the foramen cecum, located at the anterior, midline base of the tongue, to its final adult destination in the lower neck. The thyroid is attached to the tongue base by the thyroglossal duct. During the caudal descent of the gland, this duct elongates and subsequently degenerates and atrophies.
The normal developmental process of the thyroid gland during the embryonic period: Descent of the thyroid gland from the original position at foramen cecum to the adult position in lower neck along the thyroglossal duct course.  In adults, thyroid carcinoma can develop in a TDC, with an incidence of 1%, the most common being the papillary subtype. Presence of solid soft tissue elements, often nodular, within a thyroglossal cyst is highly suspicious of malignancy. Calcification within the cyst is thought to be a specific finding of carcinoma within TDC. 
The common reasons for imaging the TGDC are to confirm the presence of normal thyroid gland, confirm and characterize the cystic lesion, detect the presence of the ectopic thyroid tissue, and finally to exclude the presence of malignancy within it. Many imaging modalities are used in the work up of the TGDC preoperatively such USG, CT, MRI and thyroid scintigraphy. On sonography, TGDC commonly appears as thin walled unilocular anechoic cystic mass with posterior enhancement in this characteristic location. Multilocular cysts appearance is rare. They may also demonstrate internal echoes when proteinaceous or infected, similar to other complicated cysts. 
On CT, TGDC appears as a hypodense cystic mass with uniformly thin, peripheral rim enhancement. They may be hyperdense when there is high protein content.  Nuclear scintigraphy is usually not necessary in the evaluation of TGDC. The one exception is a cyst without normal thyroid gland; in this case, nuclear scintigraphy may be necessary to determine if the cyst contains the patient's only functional thyroid tissue as its removal during surgery results in permanent hypothyroidism. 
This condition must be differentiated from midline neck masses as branchial cleft cyst: Three times less common, and usually well away from the midline, delphian node adenopathy, dermoid cyst, thyroid cyst or thyroid neoplasm, laryngocoele, ranula, abscess, cystic hygromas.  Failure of involution of the thyroglossal duct and persistent secretion of epithelial cells lining the duct result in TGDC. More than half of all TGDC walls contain ectopic rests of thyroid tissue.
About 90% of the patients present before 10 years of age, with a second group of patients presenting in young adulthood. No gender predilection has been reported.  The main reason we present this case of TGDC with functioning ectopic thyroid tissue within it with absent normal thyroid gland in its normal location in lower neck because the high incidence of this rare developmental disorder of thyroid gland.
We report a case of 19 year euthyroid female with TGDC and absent normal thyroid gland. The TGDC was infrahyoid in location, size of 3.6 × 2.3 × 6.2 cm (Transverse X Anteroposterior X Craniocaudal dimensions). On thyroid scintigraphy, iodine uptake was seen within the TGDC from the level of hyoid bone down to suprasternal notch as rounded area corresponding to the region of cyst on correlation with CT scan images. This confirm that TGDC contain the ectopic thyroid tissue which was the patients only functioning thyroid tissue, so the patient was clinically euthyroid even normal thyroid gland was absent. This finding was important for treatment planning, as the removal of such TGDC results in permanent hypothyroidism.
Cysts located adjacent to the tongue base are lined with stratified squamous epithelium, while cysts located adjacent to the thyroid gland are lined with cells similar to those of the thyroidal acinar epithelium was noted in the literature. In our case also, TGDC was infrahyoid containing the ectopic rests of thyroid tissue.
As the case report by Martins et al.,  which revealed the rare possibility of thyroid carcinoma arising in a TGDC and it is clinically indistinguishable from a benign TGDC. 18F-FDG PET/CT was performed which revealed no FDG uptake in the TGDC suggesting no malignancy.
| Conclusion|| |
Benign TGDC are most often diagnosed clinically by typical anterior midline location in the neck. There are two goals for preoperative diagnostic testing: Documenting a normal thyroid gland or ectopic thyroid, to rule out rare possibility of thyroid carcinoma in TGDC containing thyroid tissue which required for treatment planning. Along with anatomic imaging (USG/CT/MRI), nuclear imaging (thyroid scintigraphy, 18F-FDG PET/CT) is required for the complete assessment of TGDC especially in absent normal thyroid which is important for treatment and prognosis. Thus, this case highlights the role of nuclear medicine as a diagnostic challenging modality and thus aiding in therapeutic decision.
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