Preoperative staging and risk of recurrence both determine the need for RAI therapy after surgery and the protocol for tumor surveillance (Variant 6). US Thyroid US is a routine preoperative study in all patients with thyroid cancer. The role of US is to stage the primary tumor and cervical lymph nodes. In a retrospective study of patients who had primary surgery for thyroid cancer, US detected additional sites of metastatic disease not appreciated on physical examination in 20% of patients [28]. Compared to CT, US is more accurate in predicting early extrathyroidal tumor extension and multifocal bilobar disease [29]. US has excellent resolution for lymph node morphology. Most studies find US has higher diagnostic accuracy compared to CT for preoperative evaluation of nodal disease, especially for lateral compartment nodes [29-33]. Some centers use US for routine preoperative lymph node mapping and fine-needle aspiration of suspicious lymph nodes >8 to 10 mm [31]. CT Neck Preoperative CT with IV contrast is recommended as an adjunct to US for patients with clinical suspicion for advanced disease, including invasive primary tumor or clinically apparent multiple or bulky lymph node involvement [16]. CT is a better modality than US for delineating the extent of laryngeal, tracheal, esophageal, or vascular involvement [30,33]. CT is useful in defining the inferior border of disease and in determining the extent to which mediastinal structures are involved in cases with significant caudal spread. These inferior sites cannot be visualized on US. CT can also delineate bulky nodal disease and extranodal extension that involves muscle and blood vessels [34]. In particular, CT has higher sensitivity than US in detecting lymph node metastases in the central compartment and retropharyngeal space [32]. CT should be performed with iodinated contrast in order to better assess for tumor vascular encasement and small nodal metastases with hyperenhancement and necrosis.
Thyroid Disease. Preoperative staging and risk of recurrence both determine the need for RAI therapy after surgery and the protocol for tumor surveillance (Variant 6). US Thyroid US is a routine preoperative study in all patients with thyroid cancer. The role of US is to stage the primary tumor and cervical lymph nodes. In a retrospective study of patients who had primary surgery for thyroid cancer, US detected additional sites of metastatic disease not appreciated on physical examination in 20% of patients [28]. Compared to CT, US is more accurate in predicting early extrathyroidal tumor extension and multifocal bilobar disease [29]. US has excellent resolution for lymph node morphology. Most studies find US has higher diagnostic accuracy compared to CT for preoperative evaluation of nodal disease, especially for lateral compartment nodes [29-33]. Some centers use US for routine preoperative lymph node mapping and fine-needle aspiration of suspicious lymph nodes >8 to 10 mm [31]. CT Neck Preoperative CT with IV contrast is recommended as an adjunct to US for patients with clinical suspicion for advanced disease, including invasive primary tumor or clinically apparent multiple or bulky lymph node involvement [16]. CT is a better modality than US for delineating the extent of laryngeal, tracheal, esophageal, or vascular involvement [30,33]. CT is useful in defining the inferior border of disease and in determining the extent to which mediastinal structures are involved in cases with significant caudal spread. These inferior sites cannot be visualized on US. CT can also delineate bulky nodal disease and extranodal extension that involves muscle and blood vessels [34]. In particular, CT has higher sensitivity than US in detecting lymph node metastases in the central compartment and retropharyngeal space [32]. CT should be performed with iodinated contrast in order to better assess for tumor vascular encasement and small nodal metastases with hyperenhancement and necrosis.