Ron J. Karni, MD
Associate Professor & Chief
Patients with Papillary Thyroid Carcinoma (PTC) exhibit excellent rates of disease control and survival with total thyroidectomy and post-operative radioactive iodine (RAI) therapy. In the United States, overall survival is greater than 95% despite a greater than 25% risk of nodal metastases. The literature suggests a higher risk of nodal metastases in patients with large primary sites in the thyroid gland and in patients with multifocal PTC. Nodal metastases in PTC may be more difficult to identify because of unpredictable patterns of spread. Metastases may occur in the central compartment (level VI), the lateral neck (Levels II-IV), posterior triangle (Level V), the retropharyngeal nodes, or the superior mediastinum.
The identification of nodal metastases does not confer a negative prognosis according to both the MACIS1 and AJCC (TNM)2 staging systems. Despite the low impact of neck metastases on overall survival, failure to identify and treat nodal disease may lead to significant morbidity to the patient. These patients often require higher doses of RAI and re-operation in the neck.
Because a large number of cases of papillary thyroid carcinoma are identified only after surgery for nodules with inconclusive cytology (“follicular neoplasm” or “follicular lesion”), there is often no opportunity to accurately stage the nodal disease until after surgery has been performed. During pre-operative ultrasound for a thyroid nodule, many radiology departments will not evaluate the entire central neck compartment. Even fewer radiology departments will evaluate the lateral neck compartments during a dedicated thyroid ultrasound.
During thyroid surgery for nodules with inconclusive cytology, routine central compartment neck dissection is not advocated because of potential morbidity to the recurrent laryngeal nerve (RLN) and parathyroid glands. Even in cases with pre-operative cytology strongly suggestive of PTC, routine central compartment neck dissection in the N0 neck carries an NCCN Category 2B for Consensus and Evidence, indicating “lower-level evidence and nonuniform consensus” to support the recommendation for routine central compartment neck dissection.3
However, nodal disease that presents in the central compartment following thyroidectomy presents a therapeutic dilemma. Re-operation carries a high risk of injury to the RLN and parathyroid glands. In the lateral neck, metastatic PTC that is discovered after thyroidectomy presents a smaller operative risk because these tissue planes have not been previously exposed.
Small deposits of PTC identified after thyroidectomy can often be adequately treated with RAI, but this treatment approach must be balanced with the risks of high doses of radiation. As the nodal burden of metastatic PTC increases, the risk of depleting the total recommended dose of RAI increases. For this reason, RAI is an optimal therapy in patients with no gross disease following thyroidectomy and neck dissection of the affected nodal level(s) of the neck.
Several authors have considered the role of more comprehensive imaging before initial thyroidectomy for a suspicious thyroid nodule. Cross-sectional imaging using CT scan has not been advocated because the iodinated-contrast is contraindicated before potential RAI treatment. MRI is an excellent tool for assessment of nodal adenopathy but remains expensive and is not routinely used before thyroidectomy in cases with indeterminate cytology.
Surgeon-performed ultrasound has recently been advocated in the literature as an excellent pre-operative modality for the routine evaluation of the neck in patients with a suspicious thyroid nodule.4 Ultrasound carries minimal risk to the patient, is readily performed in the office setting, and is commonly performed in most patients preparing for thyroid surgery. By extending the ultrasound survey beyond the thyroid gland to the nodals basins of the neck, non-palpable cervical lymphadenopathy may be identified. In turn, ultrasound-guided fine-needle aspiration biopsy may provide further pre-operative information regarding the extent of neck metastases. The surgeon may repeat the ultrasound intra-operative in order to direct minimally-invasive approaches to small non-palpable nodal deposits. By performing a complete cervical ultrasound survey in the per-operative setting, the surgeon enhances his/her ability to identify and treat metastatic adenopathy from PTC while minimizing morbidity from re-operation and higher doses of RAI.5