Structure
The parotid gland is the largest salivary gland of the body. It is located in the postero-lateral face, extending from the superficial skin to the carotid sheath deep to the mandible. It lies between the mastoid process posteriorly and the ramus of the mandible anteriorly. It extends over the surface of sternocleidomastoid posteriorly and the masseter muscle anteriorly. The parotid duct passes superficial to masseter, turns deeply at its anterior border and empties into the inner wall of the cheek opposite the the third molar tooth.
Contents
The parotid gland contains nerves, vessels and lymph nodes which pass through it or lie within its substance.
Arterial Structures
The external carotid artery is deepest, initially outside the gland becomes enveloped as it ascends. The posterior auricular, maxillary and superficial temporal arteries arise within the gland.
Venous Structures
The superficial temporal and maxillary veins enter the substance of the gland from above, merging to form the retromandibular vein. This divides in the inferior parotid to an anterior division (which combines with the posterior auricular vein to form the external jugular) and a posterior division was combines with the common facial vein to empty into the internal jugular.
Neural Structures
The facial nerve emerges from the styloid foramen just posterior to the parotid gland. It curves anteriorly after giving off the posterior auricular branch to enter the posterior surface of the gland. It then divides into temporal, zygomatic, buccal, mandibular and cervical branches that supply the muscles of facial expression. The facial nerve and its branches form an important landmark, dividing the parotid into superficial and deep lobes. The deep lobe is relatively inaccessible due to significant side effects arising from sacrifice of the nerves.
Lymph Nodes
Parotid lymph nodes lie in the most superficial part of the parotid. They drain lymph from the lateral forehead and the lateral orbital structures.
Relations
Superficially related to the skin.
Posteriorly, related to the sternocleidomastoid and mastoid process.
Inferiorly, related with the carotid sheath (internal carotid, internal jugular, cranial nerves IX-XII), the digastric muscle, styloid process and medial pterygoid.
Anteriorly, related to the parotid duct and masseter.
Superiorly, related to the zygomatic arch.
Neurovascular Supply
Arterial Supply
The parotid gland is supplied by small branches from the external carotid artery and its named branches.
Venous Drainage
Veins drain to the retromandibular vein and its tributaries.
Lymphatics
The parotid contains superficial lymph nodes in its superior lobe. These nodes drain deeply to the deep cervical nodes or superficially to the superficial cervical nodes.
Innervation
The skin of the parotid is supplied by the great auricular nerve (ascending from C2 and C3 branches) and the auriculotemporal branch of the maxillary nerve (V2). Secretomotor supply to the parotid is derived from the glossopharyngeal nerve (IX), via the tympanic branch, tympanic plexus, lesser petrosal nerve and the pterygopalatine ganglion.
Routes of Cancer Spread
Local Invasion
Local invasion of the parotid may lead to palsy of the facial nerves (lower motor neurone pattern). Spread to adjacent structures may cause neck or jaw pain, obstruction of the parotid duct, or ulceration of the skin.
Lymphatic Spread
From the parotid, tumours generally spread to either the deep cervical nodes (levels II and III) or superficial nodes in regions II or V.
Neurological Spread
Tumours may invade along the facial nerve, causing satellite deposits in the middle ear or posterior cranial fossa.
