T4a versus T4b tumor classifications for various sites of head and neck cancers1
| Site | T4a | T4b |
|---|---|---|
| Oral cavity | Tumor invades adjacent structures, bone, muscle of tongue, maxillary sinus, facial skin | Tumor invades masticator space, pterygoid plates, or skull base and/or encases internal carotid artery |
| Oropharynx | Tumor invades the larynx, deep muscle of tongue, medial pterygoid, hard palate, or mandible | Tumor invades lateral pterygoid muscle, pterygoid plates, lateral nasopharynx, or skull base or encases carotid artery |
| Hypopharynx | Tumor invades thyroid/cricoid cartilage, hyoid bone, thyroid gland, esophagus, or central compartment | Tumor invades prevertebral fascia, encases carotid artery, or involves mediastinal structures |
| Supraglottis, glottis, subglottis | Tumor invades through the thyroid cartilage and/or invades tissues beyond the larynx (e.g. trachea or esophagus) | Tumor invades prevertebral fascia, encases carotid artery, or invades mediastinal structures |
| Maxillary sinus, nasal cavity, ethmoid sinus | Tumor invades anterior orbital contents, skin of cheek, pterygoid plates, infratemporal fossa, cribriform plate, sphenoid or frontal sinus | Tumor invades orbital apex, dura, brain, middle cranial fossa, cranial nerves other than V2, nasopharynx, or clivus |
| Salivary glands | Tumor invades skin, mandible, ear canal, and/or facial nerve | Tumor invades skull base and/or pterygoid plates and/or encases carotid artery |
| Thyroid | Tumor grows outside the thyroid capsule into subcutaneous tissue, larynx, trachea, esophagus, recurrent laryngeal nerve | Tumor invades prevertebral fascia or encases carotid arteries or mediastinal vessels |