Evaluation of a Soft, Mobile Neck Mass Below the Adam's Apple with Normal Thyroid Function
Immediate Next Step: Thyroid Ultrasound
The next step is to obtain a thyroid ultrasound to characterize this mass, determine its layer of origin, and assess for features suggesting malignancy. 1
Rationale for Ultrasound as First-Line Imaging
Ultrasound is the preferred first-line imaging modality for evaluating neck masses in the thyroid region when TSH is normal (euthyroid state), as it provides superior morphological evaluation and can detect lesions as small as 2 mm. 1, 2
The soft, mobile characteristics suggest a benign process (possibly a lipoma if it demonstrates the "pillow sign," a cyst, or a benign thyroid nodule), but ultrasound is essential to confirm the diagnosis and rule out malignancy. 3
Ultrasound can distinguish between intramural thyroid lesions and extramural compression with high sensitivity (89-98%) and will determine the exact size, layer of origin, and morphologic features of the mass. 3
Why Not Radionuclide Scanning
A thyroid uptake scan should NOT be performed in this euthyroid patient (normal TSH). 1
Radionuclide scanning is only indicated when TSH is suppressed (low), as it has low diagnostic value in euthyroid patients and wastes resources. 1
Proceeding directly to uptake scan in euthyroid patients is explicitly not recommended, as it does not help determine malignancy risk and has a low positive predictive value for cancer. 1
Ultrasound-Guided Next Steps
Based on ultrasound findings, the evaluation pathway diverges:
If the mass appears benign (smooth margins, homogeneous, well-circumscribed):
- Small, well-circumscribed lesions are typically benign, whereas irregular margins that invade other layers suggest malignancy. 3
- If the mass is anechoic (cystic), Doppler can assess for blood flow to differentiate vascular lesions. 3
- If consistent with a simple lipoma or cyst, no further intervention may be needed beyond clinical follow-up.
If the mass has suspicious features:
- Ultrasound can identify suspicious features requiring biopsy, including irregular margins, heterogeneous echotexture, microcalcifications, or invasion into adjacent structures. 1
- Ultrasound-guided fine-needle aspiration biopsy (FNAB) should be performed for solid nodules with concerning characteristics to obtain tissue for cytologic examination. 2
Critical Pitfalls to Avoid
Do NOT skip ultrasound and proceed directly to radionuclide scanning in a euthyroid patient—this misses structural abnormalities and coexisting nodules that may require biopsy for malignancy evaluation. 1
Do NOT assume normal thyroid function tests exclude a thyroid-related mass—benign and malignant thyroid nodules commonly occur in euthyroid patients. 1
Do NOT perform biopsy before ultrasound characterization, especially if there is any concern the lesion could be vascular or cystic, as probing should be done cautiously. 3
If the mass is firm on palpation, further evaluation with ultrasound is mandatory, as soft mobile masses with a positive "pillow sign" suggest lipoma, but firm masses require imaging characterization. 3
Additional Considerations
For masses larger than 3 cm or those with suspected extension beyond the thyroid gland (substernal, retropharyngeal, or mediastinal), CT or MRI may be indicated after initial ultrasound evaluation. 2
The location "under the Adam's apple" suggests a thyroid or thyroglossal duct origin, though other neck masses (lymph nodes, soft tissue tumors) remain in the differential. 2