Intrathyroidal thyroglossal duct cyst: two interesting cases and review of literature

INTRODUCTION

Thyroglossal duct cysts are congenital anomalies resulting from persistence of the epithelial tract between the origin at the foramen caecum in the tongue base to the suprasternal region. Variations in its location can be seen anywhere in the tongue, suprahyoid region, infrahyoid region and up to the supraternal notch, all along the midline of the neck.¹ Among the congenital paediatric neck masses, thyroglossal duct cysts are the most common congenital anomaly with an incidence of more than 75% of midline neck lesions.² Although thyroglossal duct cysts often occur in pediatric patients, around 50% present clinically in the second decade of life or even further later in adult life.³ Presentation of thyroglossal duct cyst as an intrathyroidal lesion is unusual and rare. Very few reports have been published in literature about this entity.

CASE SERIES

Case 1

A 25-year-old lady presented with complaints of lump in the front of neck, to the left of midline of 2 years duration. She noticed that the swelling was insidious in onset and gradually progressing in size to attain the present size. On examination, there was a swelling about 3 cm x 2 cm in size in left lobe of thyroid gland and it moved up with deglutition. The right lobe of thyroid and isthmus was normal. There were no palpable neck nodes. Laboratory investigations revealed euthyroid status. Ultrasonogram of Neck showed a large cyst about 30.1 mm x 24.7 mm in left lobe of thyroid with normal isthmus and right lobe. Fine Needle Aspiration Cytology (FNAC) of the lesion revealed dispersed benign squamous cells, few small sheets of follicular epithelial cells on a background of numerous cyst macrophages, colloid and neutrophils, being indicative of a thyroglossal duct cyst. She underwent left hemithyroidectomy under general anaesthesia. Intraoperatively, a firm nodule was seen to be occupying the entire left lobe of thyroid (Figure 1). There was no fistulous tract discernible from the thyroid lobe. Gross morphology showed an oval greyish brown nodule and cut surface showed a cystic lesion with surrounding thyroid tissue (Figure 2). Histopathological examination revealed a fibrocollagenous cyst wall lined by granulation tissue, hemosiderin laden macrophages and luminal anucleate squamous cells with congested blood vessels and colloid filled thyroid follicle (Figure 3). The specimen was negative for any malignant changes. The features were consistent with an intrathyroidal thyroglossal duct cyst. She has been symptom free after nine months of follow up.

Case 2

A 41-year-old gentleman presented with complaints of lump in the front of neck, to the left of midline of 2 months duration. He noticed that the swelling appeared recently and progressed to attain the present size. He had no other medical co-morbidities. Clinical examination revealed a soft swelling about 4 cm x3 cm in size in left lobe of thyroid gland and it moved up with deglutition. The right lobe of thyroid and isthmus was normal. No cervical lymphadenopathy was seen. He was euthyroid on laboratory investigations. Ultrasonogram of Neck revealed a large cyst about 49 mm x 43 mm x 35 mm in left lobe of thyroid with normal architecture of the isthmus and right lobe of thyroid. Fine needle aspiration cytology (FNAC) showed paucicellular smears with dispersed mature benign squamous cells and few anucleate squames on a clean background, thereby suggestive of a thyroglossal duct cyst. After counselling, he underwent left hemithyroidectomy under general anaesthesia. Intraoperatively, a cystic ballooned out nodule was seen in the left lobe of thyroid (Figure 4). Gross pathology revealed a cystic lesion at lower pole of left thyroid and cut section showed a unilocular cyst with smooth inner surface (Figure 5). Histopathological examination revealed a fibrocollagenous cyst wall lined partly by cuboidal epithelium with predominantly denuded lining. Cyst wall showed thyroid follicles filled with colloid, thin walled blood vessels and chronic inflammation (Figure 6). There was nothing suggestive of any malignant transformation. Histopathological examination was consistent with an intrathyroidal thyroglossal duct cyst. He has been on follow up of 6 months and is asymptomatic and healed well.

DISCUSSION

Thyroglossal duct cysts develop along the course of the embryonic thyroglossal duct, if any part of the duct persists after the descent of thyroid gland from the foramen caecum to the neck.⁴ A remnant tract leaves a small pouch that passes through the body of the hyoid bone and reaches its final destination anywhere above or below the thyroid gland. Cysts are formed if any material is secreted by the otherwise silent epithelial cells, thereby explaining even late onset of such lesions.⁴ They may often be silent and do not present for several years or decades till the epithelium in the tract becomes secretory in nature and starts producing mucinous material that collects and distends the tract and forms a thyroglossal duct cyst. The usual location of the cyst is midline, starting anywhere from the foramen caecum and usually presenting in infrahyoid or suprahyoid locations.

Location of a thyroglossal duct cyst in an intrathyroidal location is rare. There have been only about five such cases reported in the paediatric population.⁵ Handra-Luca et al have reported that only seven cases of intrathyroidal thyroglossal duct cysts have been reported in adults since 1998, with a predilection for the female gender.⁶ Multiple authors in literature have published isolated single case reports of intrathyroidal thyroglossal duct cysts in adults where all of them presented as a single nodule in the thyroid lobe and were suspected during aspiration cytology and were managed by thyroid lobectomy with isthmusectomy or enucleation of the cyst.^7,8,9 Saadi et al have reported an intrathyroidal thyroglossal duct cyst which presented as a midline neck mass in the isthmus of the thyroid gland that elevated with both swallowing and protrusion of tongue.¹⁰ After confirming the suspicion of a thyroglossal duct cyst using FNAC, they combined thyroidectomy and Sistrunk procedure. Intraoperatively, the cystic lesion in the thyroid isthmus had a tract extending to the hyoid bone which was also excised simultaneously.

Barber et al have described acute inflammatory manifestations of intrathyroidal thyroglossal duct cyst as acute pyogenic thyroiditis.¹¹ Hyperthyroidism was detected by them on biochemical evaluation of the patient with a tender thyroid lesion in the neck. The clinical scenario further complicated into a thyroid abscess and was managed by lobectomy. Histopathology was consistent with an intrathyroidal thyroglossal duct cyst.

The possibility of an intrathyroidal thyroglossal duct cyst is to be borne in mind in the differential diagnosis of thyroid nodules. Fine needle aspiration revealing benign squamous cells is usually diagnostic. There is also a possibility of an occult carcinoma arising within the cyst, as reported by North et al.¹²

CONCLUSION

Thyroid nodules should always be worked up with a fine needle aspiration cytology, which can be crucial in detecting a suspicion of thyroid carcinoma, intrathyroidal thyroglossal duct cyst or a colloid nodule. The treatment of choice is surgical excision comprising thyroid lobectomy and isthmusectomy and if any fistulous tract is detected intraoperatively, it also needs simultaneous excision.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: Not required

REFERENCES

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