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AN35.1-10 | Deep structures in the neck — Part 2

Cervical Lymph Nodes (AN35.5)

Classification — levels (Memorial Sloan-Kettering / AJCC):

Figure: Cervical Lymph Nodes (AN35.5)

Level	Name	Location	Drains
IA	Submental	Below symphysis between anterior digastric bellies	Floor of mouth, lower lip, chin
IB	Submandibular	Submandibular triangle	Oral cavity, anterior face
IIA/B	Upper deep cervical	Upper IJV, above hyoid	Oral cavity, nasal cavity, pharynx, parotid
III	Middle deep cervical	IJV, hyoid–cricoid	Oral cavity, oropharynx, hypopharynx
IV	Lower deep cervical	IJV, cricoid–clavicle	Hypopharynx, thyroid, oesophagus
V	Posterior triangle	Posterior to SCM	Scalp, posterior neck
VI	Central compartment	Between carotid sheaths	Thyroid, larynx, trachea, oesophagus

Jugulodigastric node (tonsillar node): large node at the junction of IJV and posterior belly of digastric — the first node enlarged in tonsillitis and tonsillar carcinoma.

Jugulo-omohyoid node: enlarged in tongue cancer.

Figure: Jugulo-omohyoid node

Virchow's node (left supraclavicular node, Level IVB/VB): enlarged in gastric/lung cancer (via thoracic duct) — Troisier's sign.

Applied anatomy: Neck node levels guide staging and surgical dissection. Radical neck dissection removes levels I–V en bloc with SCM, IJV, and accessory nerve (CN XI). Modified radical dissection preserves one or more of these three structures.

Cervical Sympathetic Chain (AN35.6)

Structure:
- 3 ganglia (superior, middle, inferior/stellate) on the prevertebral fascia, anteromedial to longus colli
- Superior cervical ganglion (largest): C2–C3 level; gives off internal carotid nerve → carotid plexus → head
- Middle cervical ganglion (inconstant): C6 level; gives off cardiac branches
- Inferior cervical ganglion (fuses with T1 → stellate ganglion): C7–T1 level; gives off cardiac and subclavian branches

Figure: Cervical Sympathetic Chain (AN35.6)

Functions:
- Sympathetic supply to the HEAD via plexuses on internal carotid and external carotid arteries
- Vasomotor, sudomotor (sweat), pilomotor supply to head and neck
- Dilates the pupil (pupillodilator fibres via superior tarsal muscle and dilator pupillae)
- Elevates the upper eyelid (superior tarsal muscle / Müller's muscle)
- Supplies the lower lid retractor

Horner syndrome — interruption of the cervical sympathetic chain:

Feature	Mechanism
Ptosis (partial)	Superior tarsal muscle (Müller) paralysis
Miosis	Dilator pupillae paralysis (sphincter pupillae unopposed)
Anhidrosis of ipsilateral face	Loss of sudomotor supply
Enophthalmos (apparent)	Lower lid elevation (upside-down ptosis)

Causes in Indian practice:
- Pancoast tumour (apical lung cancer, right > left) — most common cause; also involves C8-T1 → wasting of intrinsic hand muscles
- Carotid artery dissection (traumatic or spontaneous)
- Thyroid surgery (inadvertent damage to cervical sympathetic chain)
- Cervical lymphadenopathy (lymphoma, TB)

Cranial Nerves in the Neck: IX, X, XI, XII (AN35.7)

CN IX (Glossopharyngeal):
- Exits skull via jugular foramen
- In neck: briefly between ICA and IJV, then passes between superior and middle pharyngeal constrictors to reach the tongue
- Branches: tympanic nerve (→ lesser petrosal → parotid via auriculotemporal), carotid sinus nerve, pharyngeal branches, lingual branches
- Clinical: Carotid sinus syncope (bradycardia + hypotension from carotid massage)

Figure: Cranial Nerves in the Neck: IX, X, XI, XII (AN35.7)

CN X (Vagus) — THE key nerve of the neck:
- Exits jugular foramen, descends in carotid sheath between carotid artery (medial) and IJV (lateral)
- Right vagus: gives off right RLN at the subclavian artery (loops under it)
- Left vagus: gives off left RLN at the aortic arch (longer course — loops under arch of aorta at ligamentum arteriosum)
- Both RLNs ascend in the tracheo-oesophageal groove to enter the larynx at the cricothyroid joint
- Right RLN is more vulnerable to non-recurrent variant (0.5–1%): arises directly from the vagus → courses transversely to larynx (associated with aberrant right subclavian artery)

CN XI (Accessory):
- Exits jugular foramen → crosses the IJV (superficial or deep)
- Enters deep surface of SCM → crosses the posterior triangle (in the roof, just deep to investing fascia)
- Enters the deep surface of trapezius at the junction of upper and middle thirds
- Injury: during posterior triangle lymph node biopsy → trapezius weakness → dropped shoulder, winging of scapula, difficulty abducting arm above 90°

CN XII (Hypoglossal):
- Exits hypoglossal canal → passes between ICA and IJV
- Hooks around the occipital artery, then around the origin of the lingual artery (from ECA)
- Passes deep to posterior belly of digastric and stylohyoid muscles → enters tongue
- Ansa cervicalis (C1–C3) loops off the hypoglossal nerve — supplies the infrahyoid strap muscles (not tongue muscles)
- Injury: tongue deviates to the side of the lesion (paralysed side) + ipsilateral tongue wasting