On examination of a patient’s neck, the presence of enlarged lymph nodes may potentially indicate the presence of a primary tumour of the head and neck. This article will focus on the American Academy of Otolaryngology – Head and Neck Surgery (AAO-HNS) classification. The classification divides the neck into zones according to the primary sites of lymph node metastasis, arising from primary tumours of the aerodigestive tract.
The classification allows for aiding clinical diagnosis and indicating which nodes may be spared, permitting more targeted neck dissection, allowing preservation of neurovascular structures and thus improving functional outcomes. The neck is divided into 7 levels (see the diagram below), each level corresponds to where particular primary tumours of the aerodigestive tract commonly first metastasize to the lymphatic system. An important point to note is that the classification does not include all the nodes of the head and neck. A brief overview of the classification follows, with the anatomy of each level defined, the nodes involved and important neurovascular structures to be aware of.
The diagram shows the 7 levels where various tumours of the aerodigestive tract metastasize to.
Involvement of submental and submandibular nodes, spread is usually from tumours of the lower lip, tongue and oral cavity. Boundaries: Combined boundaries of the submandibular and submental triangles. Important structures in this area include the marginal mandibular nerve (facial nerve branch). This level can be subdivided into IA and IB by the ipsilateral anterior belly of digastric, see the diagram above.
Involvement of the upper jugular nodes is usually from tumours of the tongue, tonsils, entire pharynx, parotid gland. Boundaries: Superiorly: base of the skull , anteriorly: Lateral edge of sternohyoid, posteriorly: Posterior border of sternocleidomastoid and the inferior border: Inferior border of the hyoid bone. Important structures in this area include the marginal mandibular nerve (facial nerve branch), glossopharyngeal, vagus, phrenic and cervical sympathetics. This level can be subdivided into IIA and IIB, by the vertical plane of the spinal accessory nerve, not seen in the above diagram.
Involvement of the middle jugular lymph nodes where metastatic spread is from the larynx, hypopharynx and thyroid. Boundaries: Superiorly: Inferior border of the hyoid bone, posteriorly: Posterior border of sternocleidomastoid, anteriorly: Lateral edge of sternohyoid and the inferior boundary: Inferior border of the cricoid cartilage. Important structures in this area include the phrenic nerve, vagus nerve, cervical sympathetics and brachial plexus.
Involvement of lower jugular nodes where spread is from the larynx, hypopharynx, thyroid and cervical oesophagus. Boundaries: Superiorly: Inferior border of the cricoid cartilage, posteriorly: Posterior border of sternocleidomastoid, anteriorly: Sternohyoid and inferiorly: Clavicle. Important structures in this region include Virchow’ node, internal jugular vein, accessory nerve, phrenic, vagus, cervical sympathetic, brachial plexus, Left (thoracic duct) or right lymphatic duct.
Involvement of nodes of the posterior triangle where spread is usually from the nasopharynx, oropharynx & skin of the posterior scalp. Posterior triangle boundaries: Anteriorly: Posterior border of sternocleidomastoid, posteriorly: Anterior border of the trapezius, inferiorly: Middle 1/3 of the clavicle, roof: Deep investing fascia and the floor: Prevertebral fascia. Important structures in this region include the accessory nerve.
Involvement of nodes in the anterior region where spread is typically from tumours of the larynx, hypopharynx, trachea, thyroid and cervical oesophagus. Boundaries of anterior region: Laterally between carotid arteries, superiorly: Hyoid bone and inferiorly: suprasternal notch. Important structures in this region include the recurrent laryngeal nerves.
Involvement of nodes in the superior mediastinum where spread is typically from tumours of thyroid, subglottis region, cervical esophagus and trachea. The boundaries of the superior mediastinum are technically from the superior thoracic aperture down to the transthoracic plane, though in this classification are defined as from the sternal notch down to the innominate artery.