Where is Parotid Gland located and what is its extent?
Parotid gland is located in the parotid region- in front and below the ear lobule. It fills the gap between the ramus of mandible and the mastoid process. Its extent is as follows:
Superiorly: it extends upto the external acoustic meatus.
Inferiorly: it reaches the upper part of carotid triangle.
Posteriorly: it overlaps sternocleidomastoid muscle.
Anteriorly: it overlaps the masseter.
Medially: it reaches till the styloid process (close to the side wall of pharynx).
A part of the anterior extension of parotid gland is sometimes detached from the remaining of the gland and is referred to as accessory parotid gland The accessory parotid gland is located between the zygomatic arch above and the parotid duct below.
Describe the capsules of Parotid Gland.
Parotid gland is surrounded by two capsules:
True capsule
- It is formed by condensation of the fibrous stroma of the gland.
False capsule (Parotid fascia)
- It is formed by splitting of investing layer of deep cervical fascia.
- Its superficial lamina passes superficial to the gland, is thick and attached to inferior border of zygomatic arch.
- Its deep lamina passes deep to the gland, is thin and is attached to the styloid process and tympanic plate. It also forms stylomandibular ligament (from tip of styloid process to angle of mandible) which separates parotid gland from submandibular gland.
Describe the gross features of Parotid Gland
Parotid gland is the largest of the salivary glands. It is purely serous in nature. It is irregular in shape (roughly 3 sided inverted pyramid) and weighs approx. 25 gm. It has
- Apex:
- apex is directed below
- overlaps posterior belly of diagastric muscle and reaches the carotid triangle.
Base:
- base is concave and directed upwards.
- it is related to external acoustic meatus and posterior part of temporomandibular joint.
Three surfaces:
- Superficial (lateral) surface
- Anteromedial surface:
- Posteromedial surface
Three borders:
- Anterior
- Posterior
- Medial
Describe the relations of Parotid Gland.
Superficial relations
Structures related to Superficial (lateral) surface
This surface is covered from superficial to deep by:
- Skin
- Superficial fascia containing:
- Anterior branch of great auricular nerve
- Preauricular (superficial parotid ) lymph nodes
- Platysma muscle fibers
- Superficial lamella of parotid fascia
- Deep parotid lymph nodes
Deep relations
Structures related to Anteromedial surface
- Ramus of mandible.
- Masseter muscle
- Medial perygoid muscle
- Lateral surface of temporomandibular joint
- Terminal branches of facial nerve
Structures related to Posteromedial surface
- Mastoid process
- Sternocleidomastoid muscle
- Posterior belly of diagastric muscle
- Styloid process and muscles attached to it
- Facial nerve enters the gland through this surface
- External carotid artery is lodged in a groove in its lower part
Styloid process separates the gland from internal carotid artery, internal jugular vein and last four ( IX, X,XI & XII) cranial nerves.
Enumerate the structures emerging from the periphery of Parotid Gland.
a. Structures emerging at the apex
- Cervical branch of facial nerve
- Anterior and posterior divisions of retromandibular vein
b. Structures emerging at the base (anterior to posterior)
- Temporal branch of facial nerve
- Superficial temporal vessels
- Auriculotemporal nerve
c. Structures emerging along the anterior border (from above downwards)
- Zygomatic branch of facial nerve
- Transverse facial artery
- Upper buccal branch of facial nerve
- Parotid duct
- Lower buccal branch of facial nerve
- Marginal mandibular branch of facial nerve
d. Structures emerging along the posterior border
- Posterior auricular branch of facial nerve
- Posterior auricular vessels
Name the structures passing through the Parotid Gland.
Structures passing through the parotid gland from superficial to deep are:
- Facial nerve and its 5 terminal branches
- Retromandibular vein
- External carotid artery and its 3 branches (posterior auricular, maxillary and superficial temporal).
Facial nerve
Facial nerve is the most superficial structure passing throughthe parotid gland. It enters the gland through the posteromedial surface and divides into five terminal branches viz. temporal, zygomatic, buccal, marginal mandibular & cervical. The terminal branches leave the gland through the anteromedial surface and emerge along its anterior border.
Retromandibular vein
It is located in the intermediate zone of the parotid gland. It is formed within the gland by union of superficial temporal and maxillary veins and is divided into anterior and posterior divisions in the lower part of the gland. Its anterior division joins facial vein to form the common facial vein and the posterior division joins posterior auricular vein to form external jugular vein.
External carotid artery
It is present in the deepest plane. It enters the parotid gland through the posteromedial surface and gives posterior auricular branch and then divides into terminal branches viz. maxillary and superficial temporal arteries.The transverse facial artery, branch of superficial artery emerge along the anterior border of the gland.
Describe briefly the Parotid duct( Stensen’s duct).
- Parotid duct is thick-walled, 5cm. long and 3mm wide.
- It emerges from the gland at the middle of its anterior border (a finger breadth below the zygomatic arch).
- It runs forward and slightly downwards on the masseter muscle.
- At the anterior border of masseter it turns medially and pierces:
- Buccal pad of fat
- Buccopharyngeal fascia
- Buccinators muscle
- Buccal mucosa
- It runs obliquely between the buccinator muscle and oral mucosa (for 1cm.) before piercing the mucosa to open into the vestibule of mouth opposite to the crown of 2nd upper molar tooth.
Describe in brief the nerve supply of Parotid Gland.
Parotid gland is supplied by :
- Parasympathetic fibers – secretomotor
- Sympathetic fibers – mainly vasomotor
- Sensory fibers
Parasympathetic fibers (Secretomotor fibers)
- Stimulation of parasympathetic fibers stimulate production of watery secretion (rich in enzymes).
- Preganglionic parsympathetic fibers arise from the inferior salivatory nucleus (in medulla oblongata) and pass in Glossophryngeal nerve which leaves the cranial cavity through the jugular foramen.
- Glossopharyngeal nerve gives tympanic branch which enters the middle ear cavity through tympanic canaliculus and participates in formation of tympanic plexus ( over promontory).
- From the tympanic plexus lesser petrosal nerve arise which leaves the cranial cavity through foramen ovale and synapse in otic ganglion (located in infratemporal fossa).
- The postganglionic fibers from the otic ganglion pass through auriculotemporal branch of mandibular nerve and supply parotid gland.
Sympathetic fibers
- Are mainly vasomotor and their stimulation produces thick sticky secretion.
- Preganglionic fibers arise from lateral horn of T1 spinal segment . They synapse in superior cervical ganglion .
- The postganglionic fibers form plexus around external carotid artery and then ascend up along maxillary artery and then middle meningeal artery to reach the parotid gland.
Sensory fibers
- They carry general sensations from the parotid gland. Auriculotemporal nerve carries the sensory fibers.
Applied Aspects
Why inflammatory parotid swelling are very painful?
It is due to unyielding nature of parotid fascia. Swelling due to inflammation cause stretching of the capsule which stimulates the branches of great auricular nerve (supplies capsule of parotid gland).
The pain is more at meal time when gustatory stimulation to gland results in increased parotid secretion which add to the pressure inside the capsule.
Patient is relieved of pain to some degree after taking meals because of release of secretions.
Frey’s Syndrome
Penetrating wounds of parotid gland may damage the auriculotemporal nerve.
During the process of regeneration, secretomotor fibers in the auriculotemporal nerve may join the sympathetic fibers in the auriculotemporal nerve and supply the sweat glands of the skin covering parotid gland. Therefore, when the person eats food , beads of perspiration appear on the skin over parotid gland because the stimulus intended for salivation produces sweat instead.
Parotid abscess is drained by horizontal incision (parallel to the branches of facial nerve ) in the parotid fascia (Hilton’s method).
This is done to avoid injury to the branches of facial nerve. the terminal branches of facial nerve run horizontally through the parotid gland.
Parotid gland is divided into superficial and deep parts which are connected by isthmus. Branches of facial nerve pass horizontally forward though the isthmus in the plane between the superficial and deep parts). This plane helps surgeons to remove parotid tumor without damaging the nerve.