An Incidental Thyroglossal Duct Cyst in an Adult Female: A Case Report

Case Report

A woman in her third decade of life was referred to the imaging department for routine sonographic follow-up examination, based on a previously identified thyroid nodule. Her medical history included a left submandibular gland neoplasm first identified with sonography in 2021, following a referral for localized pain. A 2.7-cm hypoechoic solid mass was detected and later confirmed by CT. The lesion was surgically excised without documented fine-needle aspiration (FNA), although FNA would typically precede excision. An incidental TIRADS-4 thyroid nodule was also noted during the initial sonographic examination. Subsequent follow-up sonograms confirmed the nodule’s stability. The most recent examination, prior to the current exam, was performed less than a year ago. The patient reported no current symptoms related to the neck in the interim. On objective assessment, the sonographer did not visualize or palpated any lump in the neck, especially in the midline.

In this study, performed using a LOGIQ E10 system (GE HealthCare, Wauwatosa, WI, USA) with a linear ML4-20 transducer (4–20 MHz), the thyroid gland appeared unchanged. However, a well-circumscribed cystic lesion measuring 2.3 cm was identified, at the level of the hyoid bone. As the trace measurement tool was not available, in the thyroid exam setting, the sonographer manually recorded three dimensions to capture the full extent of the lesion (See Figure 1). In addition, this cystic structure did not demonstrate any flow on color Doppler (See Figure 2). The lesion demonstrated dynamic movement and superior displacement with tongue protrusion and retraction, consistent with a TGDC (refer to QR code for video).

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Figure 1.

An oblique transverse sonogram is provided that demonstrates a well-defined cystic lesion located just to the right of the midline at the level of the hyoid bone. The right submandibular gland is also visible in the field of view (see red arrows).

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Figure 2.

A sagittal sonographic view demonstrates the cystic lesion, with no internal blood flow detected with color Doppler.

A preliminary diagnosis of TGDC was made based on the sonographic findings. A retrospective review of four previous sonographic examinations, revealed no evidence of this cystic structure detected on a review of images archived within the picture archiving and communication system (PACS) or within the associated radiology reports. In addition, an initially performed contrast-enhanced neck CT was reviewed for comparison, and no cystic lesion was identified, at the level of the hyoid bone (See Figure 3).

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Figure 3.

A sagittal image plane is provided of a contrast-enhanced neck computed tomogram (CT). This image shows no definitive evidence of a thyroglossal duct cyst (TGDC), at the level of the hyoid bone (see blue arrows).

Discussion

Thyroglossal duct cysts are occasionally identified during a routine thyroid sonography in adults, though they are more commonly encountered in pediatric patients. Branchial cleft cysts, epidermal inclusion cysts, dermoid cysts, laryngocele, thymic cyst, necrotic metastases and lymphatic malformations are some of the differential diagnoses to consider when evaluating TGDC, with sonography.^1,9 On a sonogram, any cystic structure, in close proximity to the hyoid bone, is a vital clue to the potential diagnosis of TGDC. ¹ In the current case, a TGDC was incidentally discovered during follow-up imaging of a TIRADS-4 thyroid nodule.

Thyroglossal duct cysts are formed because of failure of the involution of thyroglossal duct, after the thyroid gland descends from the foramen cecum of the tongue to its final location in the inferior neck, around the late first trimester.^1,10 TGDC appear as a painless mobile mass that tends to move with tongue protrusion. ¹¹ Sonographically, TGDC do not always manifest as unilocular, thin walled anechoic cysts. Sometimes TGDC can become infected and inflamed and might display complex echoes within. ¹²

Thyroglossal duct cysts are evaluated using sonography, MRI, or CT. On MRI, they appear hyperintense on T2-weighted images and show variable signal intensity on T1-weighted images depending on protein content. ⁶ CT typically reveals a smooth, thin-walled, fluid-density lesion near the hyoid bone. ⁶ Sonography remains the preferred initial imaging choice due to its safety, portability, and dynamic imaging capability.^6,13 In the current patient, TGDC was not visible on objective assessment, hence imaging appears to be the only method for diagnosing smaller asymptomatic TGDCs.

The diagnosis of TGDC is based on its characteristic location near the hyoid bone and its dynamic movement with tongue protrusion, which is considered pathognomonic for TGDC on sonography. ¹⁴ A review of four prior sonographic studies revealed no evidence of cystic lesions with imaging or noted in the radiology reports. Further complicating the diagnosis, a contrast-enhanced neck CT from 2021 did not demonstrate any cystic structure at the hyoid level (See Figure 3). It is suspected that the hyoid region was not thoroughly examined during the earlier sonograms, potentially leading to a missed detection. Alternatively, it is speculated that the TGDC may have developed or enlarged in the interval, specifically after the sonogram performed in 2024.

Thyroglossal duct cysts may enlarge due to infection or inflammation of the epithelial-lined duct. ¹ However, the patient had no history of TGDC surgery (e.g., Sistrunk procedure), no recent upper respiratory infection, and no local symptoms such as odynophagia. This case is notable for the apparent de novo or progressive development of a TGDC, in an asymptomatic adult, without precipitating factors. The standard treatment for symptomatic or complicated TGDCs is the Sistrunk procedure, which involves removal of the cyst, central hyoid bone, and adjacent tongue base tissue.^15,16

Although TGDCs are usually benign, there is a small risk of malignant transformation. The reported incidence ranges from 0.7% to 1.5%. ¹⁷ Papillary and squamous cell carcinoma are two of the malignancies reported in TGDC, with an incidence of 94% and 5%, respectively. ¹⁸ Squamous cell carcinoma of the TGDC has a very dismal prognosis with a mortality rate between 30% and 40%. ¹⁸ Thus, it is crucial to report any evidence of TGDC on any radiologic examination, to create a baseline for imaging the patient. Fine needle aspiration (FNA) assists in definitively diagnosing the TGDC carcinoma in suspicious cases. ¹⁷ Given the malignant potential, some authors advocate for surgical excision even in asymptomatic adult patients.^2,6,19

Conclusion

This patient case emphasized the diagnostic value of sonography in identifying incidental TGDCs, even when previous imaging appears unremarkable. Any cystic structure in the vicinity of the hyoid bone should entail the sonographer to evaluate this cystic mass scrupulously in addition to using dynamic sonographic maneuvers to diagnose this as TGDC. Detection of an asymptomatic TGDC should prompt clinical follow-up and potential specialist referral to determine the need for surgical intervention. Effective interdisciplinary collaboration between imaging professionals and surgical specialists is crucial to ensuring optimal patient care.

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