Papillary Thyroid Cancer with Microscopic Extra-thyroidal Extension

Microscopic extra-thyroidal extension occurs when thyroid cancer advances beyond the thyroid capsule into the surrounding peri-thyroidal soft tissues of fat and/or skeletal muscle, without visual evidence of this invasion (which is often called macroscopic or gross invasion). It is common, with a reported prevalence of between 11% and 44%. It must also be distinguished from major extra-thyroidal extension, which implies more advanced disease and worse prognosis. Tumors with microscopic extra-thyroidal extension may be slightly more aggressive than tumors with none, although in the absence of other important prognostic findings, prognosis can be excellent. This case discussion details possible risks for patients with microscopic extra-thyroidal extension and explores treatment options, their rationale, and available evidence to make informed treatment decisions.