AAO-HNSF Primary Care Otolaryngology Handbook

CHAPTER 14

Follicular Carcinoma Approximately 15 percent of thyroid cancers is the follicular cell type. The surgical specimen of all thyroid cancers must be sectioned completely to determine if the tumor capsule and/or lymphatic and blood vessels are invaded. The findings of capsular and/or lymphovascular invasion are essential for diagnosis and cannot be determined by a fine-needle aspi- rate. Cytopathologically, the cells may also look fairly benign on fine- needle aspirate, so many specimens are interpreted as “consistent with adenoma, cannot rule out follicular carcinoma.” This tumor metastasizes via the blood. Two major types of follicular carcinoma are microinvasive and macroinvasive . A variant is Hürthle cell carcinoma, which is a more aggressive form of follicular thyroid cancer and is marked by a high frequency (75 percent or more) of Hürthle cells. Like papillary carcinoma, follicular carcinoma has an affinity for radioac- tive iodine. Since iodine is concentrated in normal thyroid tissue, an attempt to remove all thyroid tissue allows a higher dose to be delivered to the remaining tissue, thus reducing the necessary dose. Multifocal disease is less commonly seen in follicular carcinoma. Postoperative treatment includes radioactive iodine and thyroid suppression. Medullary Carcinoma Medullary carcinoma accounts for 6–10 percent of all thyroid cancers. There are two forms: familial (10–20 percent) and sporadic . In either case, the parafollicular or C-cells are the cells of origin, and the tumor tends to be bilateral. The familial form is a component of MEN IIa and IIb. MEN IIa involves parathyroid adenoma , medullary carcinoma, and pheochromocytoma . MEN IIb does not have a parathyroid component, but includes a Marfanoid habitus and mucosal neuromas. All patients with medullary carcinoma should get a urinary metanephrine screen to determine whether there is an increase in circulating catecholamines. If this test is positive, the pheochromocytoma should be located and excised first. All first-degree relatives of patients with medullary carcinoma should be tested for calcitonin levels. Currently, it has been demonstrated that the RET proto-oncogene is positive in most patients with this disease. This oncogene can be detected by a blood test. Total thyroidectomy with paratracheal, central compartment neck dissec- tions is usually recommended. In patients with a neck mass, a modified neck dissection that encompasses all the involved levels of disease should be performed. In patients with the familial form, only abnormal

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Primary Care Otolaryngology