CASE 9749 Published on 29.01.2012

Thyroid carcinoma in a thyroglossal duct cyst

Section

Head & neck imaging

Case Type

Clinical Cases

Authors

Magalhães M, Abreu J, Duarte H, Fernandes C, Oliveira P, Malheiro L, Alves S, Carneiro C, Gouvêa M

; Email:mariapinheiromagalhaes@hotmail.com
Patient

51 years, female

Categories
Area of Interest Thyroid / Parathyroids, Head and neck ; Imaging Technique Ultrasound, Image manipulation / Reconstruction
Clinical History
A cervical ultrasound was performed in a previously healthy patient to evaluate a new painless but uncomfortable neck mass. The swelling was slightly off-midline in the anterior neck, below the level of the hyoid bone, and moved upward with tongue protusion.
Imaging Findings
The cervical ultrasound showed a heterogeneous thyroid gland, presenting one hyperechoic solid nodule with a coarse calcification (Fig. 1), one predominantly cystic nodule (12mm), and three solid hypoechoic nodules in the left lobe (smaller than 10mm). Below the hyoid bone level there was a complex cystic mass, slightly left paramedian, apparently independent from the thyroid gland (Fig. 2). This location and appearance were suggestive of thyroglossal duct cyst (TDC). There was no evidence of pathological lymph nodes along the jugular-carotid vessels. A biopsy of the hyperechoic nodule was performed and the result of pathologic examination was a papillary thyroid carcinoma. The patient underwent thyroidectomy and complete excision of the cyst, whose postsurgical pathologic examination revealed to have two tumoral nodules. All five nodules of the left thyroid lobe presented micropapillary carcinoma - reflecting multifocal disease - and also two metastatic lymph nodes were found.
Discussion
The knowledge of the embryology and anatomy of the cervical region frequently allows the differential diagnosis to be narrowed. The thyroid gland begins to develop in the 3rd week of gestation. The thyroid primordium originates at the level of the foramen caecum and descends in the neck through the mesoderm of tongue and floor of the mouth musculature. The gland reaches its final position in the inferior part of the neck, after descending anterior to the thyrohyoid membrane and the strap muscles, by the 7th week of fetal life. During its migration, the anlage of the gland leaves an epithelial tract called the thyroglossal duct, which normally involutes in the 8th-10th gestational week. [1] (Fig. 3) If any part of thyroglossal duct persists, epithelial secretions, secondary to inflammation and infection, may give rise to cystic lesions.
In fact, the TDC is the most common congenital neck mass, and usually manifests as an enlarging, painless mass. About 50% of patients present before the age of 20, but there is another group of patients presenting in young adulthood. TDCs are located in the midline (75%) or slightly off-midline (25%) and approximately 80% are located at/below the hyoid bon. The remaining are seen above the hyoid, rarely, in the floor of the mouth. Its size ranges from 0.5-6 cm (most are between 1.5-3 cm).
Sonographically, an anechoic mass with a thin outer wall in this characteristic location establishes the diagnosis. However, this classic appearance is only seen in 42% of the cases. TDCs usually appear as heterogeneous or homogeneous cystic lesions, with low-level intraluminal reflectors, but this appearence has no correlation with the presence of infection/inflammation. The US image of the TDC is nonspecific and it is difficult to establish a correlation, particularly in this case, with pappilary carcinoma involvement. Indeed, thyroid cells may remain in the duct in 5% of cases and 1% of TDC abnormalities are associated with thyroid carcinoma arising from this ectopic tissue within the duct. Most of these tumours are of the papillary type, but virtually every type of thyroid malignancies can be associated with TDC. [3]
Simple incision and drainage or partial resection leads to recurrence, thus, complete excision of the cyst is the recommended surgical approach in TDC. It involves resection of the central portion of the hyoid bone and a core of tissue following the course of the thyroglossal duct. [2, 3]
Differential Diagnosis List
Papillary carcinoma in the thyroglossal duct cyst
Thyroglossal duct cyst infection/inflammation
Lymphadenopathy
Lesion in the pyramidal lobe
Final Diagnosis
Papillary carcinoma in the thyroglossal duct cyst
Case information
URL: https://www.eurorad.org/case/9749
DOI: 10.1594/EURORAD/CASE.9749
ISSN: 1563-4086