The Neck

	The neck is that part of the body extending from the skull base superiorly to the mediastinum inferiorly. It’s described for clinical purposes as triangles as follows:
Anatomy:
Anterior triangle:
	It’s bounded anteriorly by the midline, posteriorly by the anterior border of the sternocleidomastoid muscle, and superiorly by the by the lower margin of the mandible. It’s covered by skin, superficial fascia, platysma muscle, and the investing layer of the deep cervical fascia and is subdivided into smaller triangles by the anterior and posterior bellies of the digasteric muscle and the superior belly of the omohyoid muscle into the following triangles:
1.	Submental triangle:  bounded anteriorly by the       midline of the neck laterally by the anterior belly of the digasteric muscle inferiorly by the body of the hyoid bone and the floor is formed by mylohyoid muscle. Contents of this triangle are: Submental lymph nodes and the beginning of the anterior jugular vein.
2.	Digasteric triangle: bounded anteriorly by the anterior belly of the digasteric muscle, posteriorly by the posterior belly of the digasteric muscle, superiorly by the mandible and the floor is formed by the mylohyoid, hyoglossus, and superior constrictor muscles. Contents includes:  
•	Submandibular salivary gland.
•	Facial artery deep to it.
•	Facial vein and Submandibular L.N superficial to it.
•	Hypoglossal nerve on the hyoglossus muscle deep to the gland.
•	Stylopharyngeus muscle.
•	Glossopharyngeal nerve deeply placed.
•	The lower part of the parotid gland project into the triangle.
3.	Carotid triangle: boundaries are: 
•	Superiorly: posterior belly of digasteric muscle.
•	Inferiorly:   superior belly of omohyoid muscle.
•	Posteriorly: anterior border of sternocleidomastoid muscle.
•	Floor: thyrohyoid, hyoglossus, middle and inferior constrictor muscles.
   Contents: includes the carotid sheath (common carotid artery and its divisions and branches, internal jugular veins and its tributaries, hypoglossal nerve, internal and external laryngeal nerves, accessory and vagus nerves, and part of the deep cervical L.N).
4.	Muscular triangles: boundaries are: 
•	Anteriorly: midline of the neck.
•	Superiorly: superior belly of the omohyoid muscle.
•	Inferiorly: anterior border of the   sternocleidomastoid muscle.
•	Floor: sternohyoid and sternothyroid muscles.
	Contents: thyroid gland, larynx, trachea, and oesophagus.
 Posterior triangle:
	Is bounded anteriorly by the posterior border of the sternocleidomastoid muscle, posteriorly by the anterior border of the trapezius muscle, and inferiorly by the middle third of the clavicle. Its covered by skin, superficial fascia, platysma, and the investing layer of the deep cervical fascia running through these covers the supraclavicular nerve. The floor is formed by the prevertebral muscles from above downwards (semispinalis, splenius capitis, levator scapulae, scalenius medius, and scalenius anterior) muscles. The inferior belly of the omohyoid muscle subdivides the triangle into: large (occipital) above and a small (supraclavicular) triangles bellow.
1.	Occipital triangle:  bounded by:
•	Anteriorly: by the posterior border of the sternocleidomastoid muscle.
•	Posteriorly: by the anterior border of the trapezius muscle.
•	Inferiorly: by the inferior belly of the omohyoid muscle.

2.	Supraclavicular(subclavian) triangle: bounded by:
•	Anteriorly: by the posterior border of the sternocleidomastoid muscle.
•	Posteriorly: by the anterior border of the trapezius muscle.
•	Inferiorly: by the middle third of the clavicle.

Contents of the posterior triangle:
1.	Arteries: subclavian, superficial cervical, suprascapular, and occipital.
2.	Veins: external jugular.
3.	Nerves: brachial plexus, spinal accessory nerve, and branches of the cervical plexus.
4.	Lymph nodes: these are lie around the external jugular vein and accessory nerve.

Lymphatic drainage of the neck: is of tow types
A.	 Regional groups:
	1. occipital  2. retroauricular(mastoid).  3.parotid.                       4. buccal (facial)  5. submandibular  6. submental  7. anterior cervical.  8. superficial cervical.  9. retropharyngeal  10. laryngeal.  11. tracheal.
B.   Terminal group (deep cervical group):
	     Receives all the lymphatic vessels of the head and neck, either directly  or through one of the regional groups . the terminal group is closely related to the carotid sheath, specially the internal jugular vein they are embedded in the fascia of the carotid sheath, two of these nodes are clinically called: jugulodiagastric nodes and juguloomohyoid nodes.
       	Jugulodigastric node: lies just below the posterior belly of the digastric muscle and just below and behind the angle of the mandible. It receives lymphatics from the tonsils and the tongue.
      Juguloomohyoid node: is related to the intermediate tendon of the omohyoid muscle and is associated mainly with lymphatic drainage from the tongue.
	
		The deep cervical lymph nodes receive afferent lymphatic vessels from the neighboring anatomical structures and from all other regional lymph nodes in the head and neck. The efferent vessels join to form the jugular lymph trunk which drains in the thoracic duct or the right lymphatic duct, alternatively, it may drain into the subclavian lymph trunk or independently into the brachiocephalic vein. 

Levels of lymph nodes of the neck :
	There are a number of levels or regions within the neck which contain groups of lymph nodes that represent the first echelon sites for metastases from head and neck primary sites. These are described below:

          Level (I): submental & submandibular groups:
	Includes lymph nodes in the submental and submandibular triangles.
	 Level (II): upper jugular group:
	Includes lymph nodes located around the upper third of the internal jugular vein and the adjacent spinal accessory nodes extending from the skull base down to the level of the carotid bifurcation where the digastric muscle crosses the internal jugular vein. This point relates to the to level of the hyoid bone on a computed tomographic (CT) scan.
	Level (III): middle jugular group:
	This consists of lymph nodes located around the middle third of the internal jugular vein extending from the carotid bifurcation superiorly (bottom of level II) down to the upper part of the cricoid cartilage (seen on CT scan) and represents the level where the omohyoid muscle crosses the internal jugular vein. It usually contains the jugulo-omohyoid nodes and may contain the jugulo-digastric node. 
	Level (IV): lower jugular group:
	This consists of lymph nodes located around the lower third of the internal jugular vein extending from the cricoid cartilage down to the clavicle inferiorly. It may contain some jugulo-omohyoid nodes.
	Level (V): posterior triangle group:
	These nodes are located along the lower half of the spinal accessory nerve and the transverse cervical artery. Supraclavicular nodes are also included in this group. The posterior border is the anterior border of trapezius and the anterior boundary is the posterior border of sternomastoid muscle.
 
	Level (VI): anterior compartment (visceral) group:
 	This consists of lymph nodes surrounding the midline visceral structures of the neck extending from the hyoid bone superiorly to the suprasternal notch inferiorly. The lateral border on each side is the medial border of the sternomastoid muscle. It contains the parathyroid, the paratracheal and pretracheal, the perilaryngeal and precricoid lymph nodes.
	Level (VII):
	These are the lymph nodes in the upper anterior mediastinum.

Differential diagnosis of mass in the neck
Mass in the anterior triangle:
A.	midline mass:	
1. Congenital:      a. thyroglossal. b. dermoid cyst.
2. Acquired: a. ranula.  b. Ludwig’s angina.                           c. perichondritis of the thyroid cartilage.  d. chondroma and chondrosarcoma of the thyroid cartilage. e. advanced laryngeal tumours(widening of the laryngeal framework). f. thyroid isthmus swelling. g. lymph node(prelaryngeal). h. skin and associated structures (lipoma, sebaciuos cyst). i. trauma.
    B. lateral mass: 
1. Congenital:      brancheal cyst.
2. Acquired:	a. skin and associated structures (lipoma, sebaceous cyst).  b. pharyngeal pouch.  c. neck space infections( parapharyngeal, retropharyngeal abscess).                                d. lymph node:-    1. non-neoplastic(inflammatory):   
                                               *acute.
                                                *chronic: -nonspecific.
                                                                  -specific: TB, syphilis, sarcoidosis….etc.
                                             2. neoplastic: 
                                                 *primary: lymphoma, sarcoma, & leukemia.
                                                 *secondaries (occult primary).

 
                e. neurogenic tumours:
                      1. schwannoma: neurofibroma & neurolimmoma.
                      2. paraganglioma: carotid body tumour, glomus vagalae, glomus jugularae.
                      3. post operative neuroma.

                

               f. salivary gland mass:
                       1. Non-neoplastic: parotitis, sialectasis, Sjograns syndrome, pseudoparotomegaly, metabolic & drug induced parotomegaly.
                      2.   Neoplastic: 
                             -benign: pleomorphic adenoma, Warthins tumour, oxyphil adenoma, benign lymphoepithelial tumours.
                            -malignant: mucoidepidermoid CA, adenoid cystic CA, adeno CA, CA in pleomorphic adenoma, lymphoma, SCC, & undifferentiated CA.
               g. laryngeal mass: 
                       1. Non-neoplastic: laryngocele.
                       2. neoplastic:    benign: chondroma.
                                               Malignant: SCC, chondrosarcoma.
                h. thyroid gland mass: 
                       1. Non-neoplastic: simple goiter, multinodular goiter,  diffused non-toxic goiter, thyroid nodule, & thyroiditis.
                       2. neoplastic:    benign: adenoma.
                                                Malignant: (papillary, follicular, medullary, anaplastic) CA, & lymphoma.
Mass in the posterior triangle:
A.	Congenital: cystic hygroma.
B.	Acquired: 
1.	Skin and associated structures (lipoma, sebaceous cyst).
2.	cervical rib.
3.	lymph node.
4.	neurogenic tumour: schwannoma or neuroplastoma.
5.	large osteophyte.

Thyroglossal cyst
	It occurs in the remnant of the thyroglossal duct (3/4 infrahyoid, 1/4 suprahyoid) which descent from the foramen caecum, in the junction between the anterior 2/3 and the posterior third of the tongue, to the neck in its usual position. This duct is usually atrophied later on , but if small piece remain it leads to thyroglossal cyst, its located in the midline.
	Clinically: it is mobile with swallowing and with tongue protrusion.
	Treatment: surgical excision along with body of the hyoid bone, the operation is called: Sistrunk operation.
Brancheal cyst 
	It present in the lateral part of the anterior triangle, at the junction between the upper 1/3 and the lower 2/3 of the sternomastoid muscle. It originates from the remnant of the 2nd pharyngeal pouch. it may has a trunk which is connected to the posterior tonsillar pillar.Peak age incidence is between 20-30 yrs, 60% males, and 40% females.
	Clinically: well demarcated, painless (unless infected), cystic swelling, and is immobile during swallowing.
	Treatment: surgical excision.

Cystic hygroma
	Consist of large multinodular cystic masses which are communicated or isolated. The walls are thin and contain fluid can be clearly seen. It occurs in the neck and can spread to the cheek, mouth, tongue and even the ear canal. There is no sex or site predominance (35% cheek-tongue-floor, 25% neck, 15% axilla).
	Histologically: it’s a cyst lined by a single layer of flattened endothelium with fetal fat and cholesrol crystals.
	Clinically: all symptoms are due to compression:
1.	Pain is not a feature unless the cyst infected.
2.	Dyspnea from compression of the trachea.
3.	Dysphagia from compression of the oesophagus.
4.	Facial nerve & brachial plexus affection (facial pulsy, parasthesia of the upper limb). 
5.	Sudden increase in size is either due to hemorrhage or infection.
6.	on examination: painless, soft or semi-firm swelling, brilliant on translumination, it could cross to the anterior triangle &even reach the midline.
 	Diagnosis: 
1.	History & examination.
2.	plain X-ray (tracheal displacement, mediastinal widening).
3.	CT scan.
4.	FNA: fetal fat & cholesterol crystals.
Treatment:
1.	Repeated aspiration: only when large in size causing dyspnea.
2.	surgical removal : its very difficult to remove the whole tumour, because it usually surround vital structures (vagus nerve, internal jugular vein, carotid arteries, facial nerve) and those of the cheek and parotid should be delayed as  long as possible to allow the branches of the facial nerve to grow bigger for better identification and safe dissection.