It is nice to hear that your sister had a complete uneventful surgery for her thyroid
ca. I would like to know her post operative thyroid uptake scan which will tell us about any residual thyroid tissue and also about any non palpable positive lymph nodes. Any lymph node after a cancer must be taken as due to the cancer unless proved other wise. Thyroglobulin
can be normal in some patients even with lymph node recurrence. It need not be lymphoma
. A simple FNAC and a thyroid uptake scan will rule out metastasis and even if it is positive it is treatable and curable. So u can proceed ahead. All the best.
Dr. Mohammed Ibrahim