If a Thyroglossal Duct Cyst (TDC) is suspected but the ultrasound (US) is normal, can it be missed and should a different imaging modality such as computed tomography (CT) scan or magnetic resonance imaging (MRI) be used?

Imaging Approach for Suspected Thyroglossal Duct Cyst with Normal Initial Ultrasound

When a thyroglossal duct cyst (TDC) is suspected but the initial ultrasound is normal, a CT scan should be performed as the next imaging modality, as ultrasound has only moderate sensitivity (62%) for TDC detection and can miss these lesions. 1

Limitations of Ultrasound in TDC Diagnosis

• Ultrasound is recommended as the first-line imaging modality for suspected TDC but has limited sensitivity, with studies showing that 61% of surgically confirmed TDCs were missed on prior fine-needle aspiration guided by ultrasound 1
• The diagnostic sensitivity of ultrasound for TDC is approximately 62% with a positive predictive value of 69%, meaning that a significant number of cases can be missed on initial examination 1
• Ultrasound effectiveness is reduced when evaluating deep-seated masses or those in areas with complex anatomy 2
• Ultrasound's tissue characterization capability is inferior to MRI, potentially limiting its ability to definitively identify TDCs 2

Recommended Next Steps After Normal Ultrasound

• CT scan of the neck should be performed as the next imaging step when TDC is clinically suspected despite a normal ultrasound 3, 4
• CT enables better differentiation of TDCs from other anterior triangle lesions based on location, density values, and alterations in adjacent soft tissues 4
• CT is superior for evaluating extension and defining the degree of compression of surrounding structures 5
• CT can demonstrate varied locations of TDCs that may be missed on ultrasound, including suprahyoid, transhyoid, infrahyoid, and lateral positions 3

Role of MRI as an Alternative

• MRI can be considered if CT is contraindicated or unavailable 2
• MRI offers superior soft tissue contrast compared to CT, which may help in characterizing the cystic nature of the lesion 2
• MRI has disadvantages including motion artifact in the lower neck from respiration and swallowing, which may limit its utility in some cases 2
• MRI's higher soft tissue contrast allows better detection of invasion across tissue planes and involvement of neurovascular structures if present 2

Clinical Considerations and Pitfalls

• It's important to remember that TDCs may contain malignancy (estimated at 1% of cases), with papillary thyroid cancer being the most common type 6
• Preoperative identification of a normal thyroid gland is essential before any surgical intervention for a suspected TDC to prevent inadvertent removal of the only functioning thyroid tissue 7
• The differential diagnosis for TDC includes branchial cleft cyst, lymphoepithelial cyst, thyroid gland lesions, and various causes of lymphadenopathy 1
• TDCs can present in various locations and may be confused with other lesions, necessitating thorough imaging evaluation before surgical intervention 3, 4

Follow-up Recommendations

• If clinical suspicion remains high despite normal initial ultrasound, proceed directly to CT imaging 3, 4
• If both ultrasound and CT are negative but clinical suspicion remains high, consider MRI for its superior soft tissue contrast 2
• For any suspected TDC, ensure that imaging confirms the presence of a normal thyroid gland in its expected location to rule out a solitary ectopic thyroid 7