Non-Malignant Causes of Fluctuating Submental Mass Post-Chemoradiation and Surgery for Base of Tongue SCC
The most likely non-malignant causes of a fluctuating submental mass in this clinical context are reactive lymphadenopathy from post-radiation inflammation, postoperative fluid collections (seroma/lymphocele), and post-treatment edema—all of which can wax and wane in size over time. 1
Post-Treatment Inflammatory Changes
Reactive lymph nodes are a well-recognized benign finding after chemoradiation for head and neck squamous cell carcinoma. The ACR NI-RADS guidelines specifically note that growing lymph nodes without morphologically abnormal features (such as necrosis or extranodal extension) may represent normal reactive nodes showing mild increase in size secondary to inflammation, warranting shorter follow-up or PET imaging rather than immediate biopsy. 1
- Post-radiation inflammation can cause residual nodal tissue with mild FDG uptake that fluctuates based on the degree of ongoing inflammatory response 1
- The fluctuating nature strongly suggests a benign inflammatory process rather than progressive malignancy, which typically demonstrates steady growth 1
Postoperative Fluid Collections
Postoperative seromas and lymphoceles are common after neck dissection and can present as fluctuating masses in the surgical bed. These collections may increase and decrease in size based on fluid reaccumulation and resorption patterns. 2
- Even large heterogeneous masses in the postoperative period may represent simple fluid collections rather than recurrent disease 2
- These collections can persist for months after surgery and may demonstrate heterogeneous appearance on imaging without representing malignancy 2
Post-Radiation Edema
Post-treatment edema is an expected finding after combined surgery and chemoradiation, particularly in the first 12-24 months following treatment. 1
- The ACR NI-RADS guidelines emphasize recognizing post-treatment changes that show enhancement or FDG uptake representing posttreatment change rather than tumor recurrence 1
- Edema can fluctuate based on activity level, positioning, and ongoing tissue healing 1
Diagnostic Approach to Differentiate Benign from Malignant
The ACR NI-RADS classification system provides a structured approach to evaluating post-treatment masses:
- NI-RADS Category 2: Ill-defined non-mass-like abnormalities with only mild contrast enhancement or FDG uptake suggest low suspicion for recurrence (17% rate of positive disease) and warrant short-term follow-up in 3 months or addition of PET imaging rather than immediate biopsy 1
- Key benign features include: absence of discrete nodule or mass, mild rather than intense FDG uptake, lack of morphologically abnormal features such as necrosis or extranodal extension 1
- Fluctuation in size is more consistent with benign processes than progressive malignancy, which typically shows steady growth 1
Critical Management Recommendations
For a fluctuating submental mass without high-risk imaging features, the recommended approach is:
- Short-term imaging follow-up at 3 months to assess for interval change rather than immediate biopsy 1
- Consider PET/CT if CECT findings are equivocal to assess metabolic activity 1
- Reserve biopsy for masses that demonstrate progressive growth, develop morphologically abnormal features, or show intense focal FDG uptake on PET imaging 1
Common Pitfalls to Avoid
Do not immediately assume recurrence based solely on the presence of a mass or mild FDG uptake in the post-treatment setting. The ACR guidelines specifically warn that post-treatment CECT and PET show enhancement or FDG uptake that represent posttreatment change and not tumor persistence or recurrence. 1
- Avoid premature biopsy of ill-defined, fluctuating masses without high-risk features, as these are poor biopsy targets and have low yield 1
- Recognize that the post-treatment neck has a "complicated postsurgical appearance" that is expected and should not trigger aggressive intervention without additional concerning features 1
- Understand that stable or mildly fluctuating nodal soft tissue with little to no FDG avidity can be categorized as NI-RADS 1 (expected post-treatment appearance) on subsequent surveillance studies 1