THYROID GLAND (ICD‐O C73) (FIG. 121)

Rules for Classification

The classification applies only to carcinomas, including papillary, follicular, poorly differentiated, insular, anaplastic and medullary carcinomas. There should be microscopic confirmation of the disease and division of cases by histological type.

Schematic illustration of Thyroid gland. — **Fig. 121**

Regional Lymph Nodes (Fig. 122)

The regional lymph nodes are the cervical and upper/superior mediastinal nodes

TN Clinical Classification

T – Primary Tumour

TX	Primary tumour cannot be assessed
T0	No evidence of primary tumour
T1	Tumour 2 cm or less in greatest dimension, limited to the thyroid (Fig. 123)
	T1a	Tumour 1 cm or less in greatest dimension, minimal extrathyroidal extension may be present
	T1b	Tumour more than 1 cm but not more than 2 cm in greatest dimension, minimal extrathyroidal extension may be present
	T2	Tumour more than 2 cm but not more than 4 cm in greatest dimension, minimal extrathyroidal extension may be present (Fig. 124, 125)

Schematic illustration of Regional Lymph Nodes. — **Fig. 122**

Schematic illustration of tumour 2 cm or less in greatest dimension, limited to the thyroid. — **Fig. 123**

Schematic illustration of tumour more than 2 cm but not more than 4 cm in greatest dimension, minimal extrathyroidal extension. — **Fig. 124**

Schematic illustration of tumour more than 2 cm but not more than 4 cm in greatest dimension, minimal extrathyroidal extension may be present. — **Fig. 125**

T3a	Tumour more than 4 cm in greatest dimension, limited to the thyroid or with minimal extrathyroid extension (Fig. 126)
T3b	Tumour of any size with gross extrathyroid extension invading the strap muscles (e.g., extension to sternohyoid, sternothyroid or omohyoid muscles)

T4a	Tumour extends beyond the thyroid capsule and invades any of the following: subcutaneous soft tissues, larynx, trachea, oesophagus, recurrent laryngeal nerve (Figs. 127, 128)
T4b	Tumour invades prevertebral fascia, mediastinal vessels, or encases carotid artery (Fig. 129)

Schematic illustration of tumour more than 4 cm in greatest dimension, limited to the thyroid or with minimal extrathyroid extension. — **Fig. 126**

Schematic illustration of tumour extends beyond the thyroid capsule and invades subcutaneous soft tissues, larynx, trachea, oesophagus, recurrent laryngeal nerve. — **Fig. 127**

Photo depicts the Tumour extends beyond the thyroid capsule and invades subcutaneous soft tissues, larynx, trachea, oesophagus, recurrent laryngeal nerve. — **Fig. 128**

Schematic illustration of tumour invades prevertebral fascia, mediastinal vessels, or encases carotid artery. — **Fig. 129**

N – Regional Lymph Nodes

NX	Regional lymph nodes cannot be assessed
N0	No regional lymph node metastasis
N1	Regional lymph node metastasis
	N1a	Metastasis in Level VI (pretracheal, paratracheal and prelaryngeal/Delphian lymph nodes) or upper/superior mediastinum (Fig. 130)
	N1b	Metastasis in other unilateral, bilateral or contralateral cervical (Levels I, II, III, IV or V) or retropharyngeal (Fig. 131)