True follicular carcinomas are far less common than papillary cancer and are now rather uncommon. Remember that the “follicular variant” of papillary cancer should be classified and treated as a papillary carcinoma. Patients with follicular carcinoma are usually older than those with papillary cancer, and once more, females predominate. Microscopically, the diagnosis of follicular cancer is made when vascular and/or capsular invasion is present. Tumor multicentricity and lymph node metastases are far less common than in papillary carcinoma. Metastatic spread of tumor often occurs by hematogenous dissemination to the lungs, bones, and other peripheral tissues.

A follicular cancer that demonstrates only microinvasion of the capsule has a very good prognosis (37). In this situation, ipsilateral lobectomy is probably sufficient. However, for most patients with follicular cancer that demonstrates gross capsular invasion or vascular invasion, the ideal operation is similar to that for papillary cancer, although the rationale for its performance differs. Near-total or total thyroidectomy should be performed not because of multicentricity but rather to facilitate later radioiodine treatment (36). Remnants of normal thyroid in the neck are ablated by radioiodine, and if peripheral metastases are detected (Fig. 14), they should be treated with high-dose radioiodine therapy. Although lymph node metastases in the lateral region of the neck are not commonly found, a modified radical neck dissection should be performed if large palpable metastatic nodes are present.

Finally, regardless of the operation, all patients with papillary or follicular cancer should be treated for life with levothyroxine therapy in sufficient doses to suppress the TSH level (36). Care should be taken to not cause cardiac or other problems from thyrotoxicosis, however, and not to cause osteoporosis.