The Parotid Gland
The parotid gland, the largest of all three head salivary glands, is located in the parotideomasseteric region. This pyramidal-shaped gland secretes purely serous saliva and its contribution makes up approximately thirty percent of the total saliva output.
The gland is bilateral, paired and sits on either side of the face in the preauricular area, behind and upon the mandibular ramus. There it is encapsulated by the masseteric fascia deriving from the deep cervical fascia. The parotid plexus, branches of the facial nerve, passes through the parotid gland and divides it into a superficial and a deep part but does not innervate it. The parotid duct (also known as Stensen's duct) drains the saliva into the oral cavity opposite the upper second molar tooth via the parotid papilla. In its course it crosses the masseter and pierces through the buccinator. Gland tissues along the parotid duct and lying on the masseter muscle are referred to as accessory parotid glands.
The parotid is bordered anteriorly by the masseter muscle and the mandibular ramus and superiorly by the external acoustic meatus and the condyle of the mandible in the glenoid fossa. Posterior to the gland is the mastoid process of the temporal bone and the sternocleidomastoid muscle and inferiorly the angular tract of Eisler can be found. On the medial side which is not covered by the capsule the styloid process and the transverse process of the atlas are visible.
Due to the constant production of saliva, especially during meal times, the parotid gland is well perfused. The maxillary arteries and superficial temporal arteries - two terminal branches of the external carotid artery - provide the major blood supply. The venous blood drains to the retromandibular (or posterior facial) vein which runs lateral to the carotid artery.
The parotid gland is innervated by various nerves from different sources. The sensory innervation is provided by the auriculotemporal nerve deriving from the mandibular branch of the trigeminal nerve. The parasympathetic innervation which stimulates the saliva production is carried from the glossopharyngeal nerve to the otic ganglion via the lesser petrosal nerve. From there the parasympathetic postganglionic neurons reach the gland via the auriculotemporal nerve. Furthermore the gland receives sympathetic innervation from direct fibers of the external carotid plexus.
The parotid gland and its surrounding structures can be subject to different pathologies such as nerve damages, infections, cysts, fistulae and tumors.
In Frey’s syndrome (also known as auriculotemporal syndrome) autonomic fibers from the auriculotemporal nerve regenerate after parotidectomy and innervate the surrounding sweat glands. Typically the affected patients complain about sweating and flushing during meals.
Tumors can occur in the gland, however 80% of them prove to be benign.
Mumps is a common viral infection affecting young children causing fever, vomiting and a typical swelling of the parotid glands.
Lastly, a parotid fistula is a tubular connection between the skin of the cheek and the parotid gland itself, which can cause a sialocele; a cyst containing saliva and tissue.