"Parotid Gland" PDF - Lecture Notes

The parotid gland Lecture 13 The parotid gland is a bilateral salivary gland located in the face. It produces serous saliva (a watery solution rich in enzymes) which is then secreted into the...

The parotid gland Lecture 13 The parotid gland is a bilateral salivary gland located in the face. It produces serous saliva (a watery solution rich in enzymes) which is then secreted into the oral cavity, where it lubricates and aids in the breakdown of food. Anatomical Position The parotid gland is a bilateral structure, which displays a lobular and irregular morphology. Anatomically, it can be divided into deep and superficial lobes, which are separated by the facial nerve. It lies within a deep hollow, known as the parotid region. The parotid region is bounded as follows: Superiorly: Zygomatic arch. Inferiorly: Inferior border of the mandible. Anteriorly: Masseter muscle. Posteriorly: External ear and sternocleidomastoid. The secretions of the parotid gland are transported to the oral cavity by the Stensen duct. It arises from the anterior surface of the gland, traversing the masseter muscle. The duct then pierces the buccinator, moving medially to enter the vestibule of the mouth upon a small papilla opposite the upper second molar tooth. Anatomical Relationships The anatomical relationships of the parotid gland are of great clinical importance – particularly during parotid gland surgery. Several important neurovascular structures pass through the gland: 1- Facial nerve (CN VII): gives rise to five terminal branches within the parotid gland. These branches innervate the muscles of facial expression. 2- External carotid artery: gives rise to the posterior auricular artery within the parotid gland. It then divides into its two terminal branches (the maxillary artery and superficial temporal artery). 3- Retromandibular vein: formed within the parotid gland by the convergence of the superficial temporal and maxillary veins. It is one of the major structures responsible for venous drainage of the face. Arterial supply: by the posterior auricular and superficial temporal arteries. They are both branches of the external carotid artery, which arise within the parotid gland itself. Venous drainage: is achieved via the retromandibular vein. It is formed by unification of the superficial temporal and maxillary veins. Innervation: The parotid gland receives sensory and autonomic innervation. The autonomic innervation controls the rate of saliva production. Sensory innervation is supplied by the auriculotemporal nerve (gland) and the great auricular nerve (fascia). The parasympathetic innervation to the parotid gland has a complex path. It begins with the glossopharyngeal nerve then the nerves reach the gland via the lesser petrosal nerve to the otic ganglion. The auriculotemporal nerve then carries parasympathetic fibres from the otic ganglion to the parotid gland. Parasympathetic stimulation causes an increase in saliva production. Sympathetic innervation originates from the superior cervical ganglion (part of the paravertebral chain). Fibres from this ganglion travel along the external carotid artery to reach the parotid gland. Increased activity of the sympathetic nervous system inhibits saliva secretion, via vasoconstriction. Lymphatic drainage: There are numerous lymph nodes distributed throughout and around the substance of the parotid gland. This is an exception to the norm as all other salivary glands (both major and minor) do not have lymph nodes within the glandular tissue and have far fewer nodes surrounding them. The lymph nodes of the parotid gland are distributed throughout the superficial and deep lobes of the gland. The majority of the lymph nodes (about 90%) are found in the superficial node. The nodes themselves are situated close to the surface of the gland, between the capsule and glandular tissue. a) The superficial set of lymph nodes drains the external acoustic meatus, auricle (pinna), scalp, eyelids, and lacrimal glands in addition to the parotid gland. b) The deep set of lymph nodes drains other structures in addition to the parotid gland: external acoustic meatus, soft palate, middle ear, and nasopharynx.  The parotid gland Lecture 14 The buccal fat pad: It is one of several encapsulated fat masses in the cheek. It is a deep fat pad located on either side of the face between the buccinator muscle and several more superficial muscles (including the masseter, the zygomaticus major, and the zygomaticus minor). The inferior portion of the buccal fat pad is contained within the buccal space. It should not be confused with the malar fat pad, which is directly below the skin of the cheek. It should also not be confused with jowl fat pads. It is implicated in the formation of hollow cheeks and the nasolabial fold, but not in the formation of jowls. The buccal fat pad is composed of several parts, although exactly how many parts seems to be a point of disagreement and no single consistent nomenclature of these parts has been observed. It was described as being divided into three lobes, the anterior, intermediate, and posterior, "according to the structure of the lobar envelopes, the formation of ligaments, and the source of the nutritional vessels". Also, there are four extensions from the body of the buccal fat pad: the sublevator, the melolabial, the buccal, and the pterygoid. The nomenclature of these extensions derives from their location and proximal muscles. The anterior lobe of the buccal fat surrounds the parotid duct, which conveys saliva from the parotid gland to the mouth. It is a triangular mass with one vertex at the buccinators, one at the levator labii superioris alaeque nasi, and one at the orbicularis oris. The intermediate lobe lies between the anterior and posterior lobes over the maxilla. The intermediate lobe seems to lose a significant amount of volume between childhood and adulthood. The posterior lobe of the buccal fat pad runs from the infraorbital fissure and temporal muscle to the upper rim of the mandible and back to the mandibular ramus. Some people describe the buccal fat pad's primary function in relation to chewing and suckling, especially in infants. This theory derives some support from the loss of volume to the intermediate lobe, which would be most directly involved in chewing and sucking, from infancy to adulthood. Another proposed function is as gliding pads that facilitate the action of the muscles of mastication. The buccal fat pad may also function as a cushion to protect sensitive facial muscles from injury due to muscle action or exterior force. Clinical Relevance: Disorders of the Parotid Gland Parotid Gland Tumours The parotid gland is the most common site of a salivary gland tumour. These tumours are usually benign, such as an adenolymphoma. In contrast, tumours of the submandibular and sublingual glands are less common, but more likely to be malignant. Treatment usually involves surgical excision of the tumour and parotid gland, known as a parotidectomy. During this procedure, it is critical to identify and preserve the facial nerve and its branches. Damage to facial nerve or its branches will cause paralysis of the facial muscles. The affected muscles will lose tone, and the area will ‘sag’. The inferior eyelid can be particularly affected, falling away from the eyeball (known as ectropion). Parotitis Parotitis refers to inflammation of the parotid gland, usually as a result of an infection. The parotid gland is enclosed in a tough fibrous capsule. This limits swelling of the gland, producing pain. The pain produced can be referred to the external ear,why? This is because the auriculotemporal nerve provides sensory innervation to the parotid gland and the external ear. Parotid Duct Injury The parotid duct, which is a comparatively superficial structure on the face, may be damaged in injuries to the face or may be inadvertently cut during surgical operations on the face. The duct is about 2 in. (5 cm) long and passes forward across the masseter about a fingerbreadth below the zygomatic arch. It then pierces the buccinator muscle to enter the mouth opposite the upper second molar tooth. Parotid Salivary Gland and Lesions of the Facial Nerve The parotid salivary gland consists essentially of superficial and deep parts, and the important facial nerve lies in the interval between these parts. A benign parotid neoplasm rarely, if ever, causes facial palsy. A malignant tumor of the parotid is usually highly invasive and quickly involves the facial nerve, causing unilateral facial paralysis. The parotid gland may become acutely inflamed as a result of retrograde bacterial infection from the mouth via the parotid duct. The gland may also become infected via the bloodstream, as in mumps. In both cases the gland is swollen; it is painful because the fascial capsule derived from the investing layer of deep cervical fascia is strong and limits the swelling of the gland. The swollen glenoid process, which extends medially behind the temporomandibular joint, is responsible for the pain experienced in acute parotitis when eating. Frey's Syndrome Frey's syndrome is an interesting complication that sometimes develops after penetrating wounds of the parotid gland. When the patient eats, beads of perspiration appear on the skin covering the parotid. This condition is caused by damage to the auriculotemporal and great auricular nerves. During the process of healing, the parasympathetic secretomotor fibers in the auriculotemporal nerve grow out and join the distal end of the great auricular nerve. Eventually, these fibers reach the sweat glands in the facial skin. By this means, a stimulus intended for saliva production produces sweat secretion instead.