Thyroid Dysfunction _________________________________________________________________________
DIAGNOSIS Thyroid cancer is diagnosed in several ways. The simplest test is fine-needle aspiration of the thyroid nodule. Although a blood test cannot provide a definite diagnosis of cancer, it can assess the overall condition of the thyroid gland, which is helpful in determining a diagnosis. A nuclear thyroid scan, as described earlier, may be helpful both in diagnosis of the primary tumor and in determining metastasis. Ultrasound is an excellent noninvasive method of determining the number and size of nodules but cannot determine the pathology. Additional use of computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET) scan, and vocal cord exam may also be useful. Ultimately, a biopsy is required for definitive diagnosis [31; 38] .
STAGING Staging of thyroid cancer can help determine treatment options and predict the patient’s prognosis. The American Joint Committee on Cancer (AJCC) has developed the TNM method of staging, which involves assessing three aspects of the cancer. T denotes the size of the tumor, N refers to the extent of metastasis to regional lymph nodes, and M indicates whether the cancer has metastasized to other organs ( Table 2 ). After the TNM classification is complete, the carcinoma may be staged and prognosis estimated ( Table 3 , Table 4 , and Table 5 ) [39; 40; 41] .
AMERICAN JOINT COMMITTEE ON CANCER TNM CLASSIFICATION FOR THYROID CANCER Code Description Primary Tumor (T) a TX Primary tumor cannot be assessed T0 No evidence of primary tumor T1a Tumor 1 cm or less in greatest dimension, limited to the thyroid T1b Tumor larger than 1 cm but not larger than 2 cm in greatest dimension, limited to the thyroid T2 Tumor larger than 2 cm but 4 cm or smaller in greatest dimension, limited to the thyroid T3 Tumor larger than 4 cm in greatest dimension limited to the thyroid or any tumor with minimal extrathyroid extension
T4a (non- anaplastic)
Tumor of any size extending beyond the thyroid capsule to invade subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve
T4a (anaplastic) Tumor limited to the thyroid T4b (non- anaplastic)
Tumor invades prevertebral fascia or encases carotid artery or mediastinal vessels
T4b (anaplastic) Tumor has extended beyond the thyroid Regional Lymph Node Involvement (N) NX Regional lymph nodes cannot be assessed N0 No regional lymph node involvement N0a
One or more cytologically or histologically confirmed benign lymph node No radiologic or clinical evidence of locoregional lymph node metastasis
N0b
N1
Metastasis to regional lymph nodes
N1a
Metastasis to level VI or VII (pretracheal, paratracheal, and prelaryngeal/Delphian, or upper mediastinal lymph nodes) Metastasis to unilateral or bilateral cervical, retropharyngeal, or superior mediastinal lymph nodes
N1b
Distant Metastasis (M) MX
Distant metastasis cannot be assessed
M0 M1
No distant metastasis
Distant metastasis is present a All categories may be subdivided into (a) solitary tumor or (b) multifocal tumor. Source: [24; 39; 40]
Table 2
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