Book 4 - Self Instructional Manual for Cancer Registrars - SEER ...

ThyroidGlandThe thyroid gland consists of two lateral lobes united by a strip of glandular tissue called theisthmus. It is covered by two capsules: an inner capsule of fibroelastic tissue and an outer capsulecontinuous with and part of the deep cervical fascia. The thyroid is located on either side of thetrachea just below the thyroid cartilage. The unit structure of the thyroid gland is the follicle. Athin, continuous basal membrane surrounds each follicle. Between the follicles are capillaries,fibroblasts, and small bundles of collagenous fibers. This gland produces the hormones thyroxin andtri-iodothyronine which are necessary to maintain a normal level of metabolism in all body cells.These hormones are synthesized in the thyroid gland from iodine. Another hormone produced bythe thyroid gland is thyrocalcitonin which aids in maintaining the proper level of calcium in the blood.In summary, the main physiological actions of this gland are to assist in regulating the metabolic ratein concert with growth and tissue regulation.Lymphatic drainage is to cervical and mediastinal nodes:Delphian nodeAnterior cervical: prelaryngeal, pretracheal, laterotracheal (recurrentlaryngeal nerve chain)Internal jugular: jugulodigastric and jugulo-omohyoidTracheoesophagealMediastinal, upper anterior and posterior (tracheoesophageal)RetropharyngealTumorsMalignant tumors of the thyroid are primarily of two main types:• Papillaly adenocarcinoma is the most common thyroid cancer. It is generally welldifferentiated and characterized by well-defined papillary fronds. Spread is usuallyvia the lymphatics to the cervical lymph nodes. Prognosis is good following excisionof the involved lobe(s). Lymph node dissection may be deferred until there isclinical evidence of nodal involvement.• Follictdar adenocaminoma is the second most common type of thyroid malignancy.It has well-developed follicles resembling normal thyroid tissue. Dissemination isusually via the blood stream to distant sites.Mixed papillary and follicular carcinoma is common. It behaves like papillary carcinoma.• Medullary calvinoma with amyloid stroma is a rare tumor.• Anaplastic carcinoma is also rare; it occurs predominantly in older patients.The most common bcnign tumor of thc thyroid is the adenoma of which there are several types,such as: papillary, tk)llicular, colloid, fetal, and Hurthlc cell_ These benign tumors are not generallyincluded in the cancer registry unless they are of special interest to the medical staff.331