16 parotid bed Lama El Banna

2.  The parotid bed is an irregular space
located between the ramus of the
mandible, the external acoustic meatus
and the mastoid and styloid processes,
the digastric muscles, and
sternocleidomastoid muscle.

4.  The medial extent of this bed is bordered by the
posterior belly of the digastric muscle and the
muscles attached to the styloid process. Inferiorly,
the bed is bounded by the superoanterior border of
the sternocleidomastoid muscle. This somewhat
irregularly-shaped area houses the parotid gland,
which is molded into this space, thus assisting in
filling out the contour of the jaw/neck/ear junction.
 Representatives of two cranial nerves—the facial
nerve and trigeminal nerve—pass through the
substance of the parotid gland to reach their
destinations in and about the head and neck.
 Similarly, the external carotid artery and some of
its branches course through the gland, as do some
of the tributaries forming the external jugular vein.

5.  The parotid gland is the largest of the three major
salivary glands (parotid, submandibular, and
sublingual glands) and is enclosed within a capsule
that is part of the deep cervical fascia. It is located on
the lateral aspect of the face and in the parotid bed.
 Because the gland is molded into an irregular space, it
is also irregular in shape. The superficial aspect of the
gland extends superiorly over the masseter muscle to
the zygomatic arch, where an accessory portion of the
gland may be detached from the main substance.

7.  Inferiorly, it is mostly confined to the region between the
mastoid process, the sternocleidomastoid muscle, and the
angle of the mandible, where it extends over the posterior
aspect of the masseter muscle.
 Medially, the gland extends into the deeper portions of the
parotid bed to the styloid process and its attached
musculature. Here, a wedge-shaped portion of the gland
may intervene between the medial and lateral pterygoid
muscles for a short distance. Often, glandular lobes extend
into other spaces adjacent to the parotid bed.
 One such lobe passes between the ramus of the mandible
and the medial pterygoid muscle (above that muscle's
insertion), whereas other lobes pass between the external
auditory meatus and the temporomandibular joint (TMJ)
and between the external carotid artery and the superior
constrictor muscle of the pharynx.

9.  Exiting the anterior aspect of the superficial
portion of the gland is the parotid duct (Stenson
duct), which passes anteriorly, superficial to the
masseter muscle, to dive medially into the buccal
fat pad; it pierces the buccinator muscle on its way
to the oral vestibule. It delivers the parotid salivary
secretions at the opening of the parotid papilla
located opposite the second maxillary molar.

10.  Because the parotid gland is irregular in shape,
possessing many fingerlike projections radiating
in several directions from the parotid bed, the
gland associates with or engulfs many of the
structures passing through this region.
 Structures associated with the superficial aspect
of the gland include branches of the great
auricular nerve originating from the cervical
plexus that provide sensory innervation to the
region, and small lymph nodes that drain the
superficial area.

12.  Structures associated with the deep aspect of the
gland, provided it sends projections medial to the
styloid process, include the external and internal
carotid arteries, the internal jugular vein, and both
the vagus and glossopharyngeal nerves.
 Several structures pass through the gland. The
external carotid artery enters the substance of the
gland, and it is there that several of its branches
arise, including the posterior auricular, maxillary,
and superficial temporal arteries. The
retromandibular vein, as well as the veins uniting
to form it, also pass through the gland.

13.  The facial nerve (cranial nerve VII), exits the
stylomastoid foramen and enters the substance of
the gland. While in the gland, the facial nerve
forms a plexus before exiting the gland to
innervate the muscles of facial expression.
 The auriculotemporal nerve, a branch of the
mandibular division of the trigeminal nerve (cranial
nerve V), enters the substance of the gland from
its deep aspect along the neck of the mandible
and emerges from the gland just inferior to the
root of the zygomatic arch. While within the gland,
it communicates with the facial nerve and
distributes fibers to the gland.

14.  The structures entering the parotid gland exit from its
posterior, superior, inferior, and anterior surfaces.
 The posterior auricular artery exits from the posterior
aspect of the gland.
 The superficial temporal artery and vein,
auriculotemporal nerve, and temporal branches of the
facial nerve may be observed at the superior margin of
the gland.
 Inferiorly, the retromandibular vein exits the parotid
gland just before joining the posterior auricular vein to
form the external jugular vein. Emanating from the
entire facial margin of the gland are the terminal
branches of the facial nerve, grouped into five major
branches: the temporal, zygomatic, buccal,
mandibular, and cervical branches.

16.  The posterior auricular artery, arising from the
external carotid artery within the substance of the
parotid gland, provides branches that vascularize
the gland. Additional small glandular branches
arising from the superficial temporal and
transverse facial arteries also supply the gland.
Venous drainage is via the tributaries passing
through the gland, and these vessels empty into
the external jugular vein.

17.  Lymph percolating through lymph nodes located
superficially and within the substance of the gland
is delivered into the superficial and deep cervical
lymph nodes.

18.  The parotid gland receives sensory and autonomic
innervation. General sensation is provided by branches
of the great auricular nerve, from the cervical plexus, as
it ramifies over the surface of the gland.
 The sympathetic component of the autonomic nervous
system reaches the gland via postganglionic
sympathetic fibers derived from the carotid plexus; these
fibers travel on the external carotid artery and its
branches that course through the gland. Sympathetic
innervation to the parotid gland mediates
vasoconstriction to these vessels.

19.  Parasympathetic innervation is distributed to the gland
by the auriculotemporal nerve [a branch of the
trigeminal nerve (cranial nerve V)], even though these
parasympathetic fibers do not arise within the
trigeminal complex. Preganglionic parasympathetic
fibers, from the glossopharyngeal nerve (cranial nerve
IX), pass from its tympanic branch via the lesser
petrosal nerve to the otic ganglion, where they
synapse on postganglionic cell bodies. Postganglionic
parasympathetic fibers from here then join the
auriculotemporal branch of the mandibular division of
the trigeminal nerve, to be distributed to the gland
effecting secretomotor functions

20.  Several arteries either originate in or are in
close association with the parotid bed. These
are the ascending pharyngeal, occipital,
posterior auricular, maxillary, and superficial
temporal arteries.

21.  The facial nerve, cranial nerve VII, exits from the cranial cavity at the
stylomastoid foramen located in the temporal bone just posterior to the
styloid process. On exiting, it communicates with the glossopharyngeal
and vagus nerves and with the great auricular nerve of the cervical
plexus.
 The auriculotemporal nerve from the mandibular division of the
trigeminal nerve communicates with the facial nerve after it has entered
the substance of the parotid gland. Presumably, this communication
provides general sensory fibers from the trigeminal nerve to the facial
nerve for distribution to the face. Branches arising from the facial nerve
as it passes through this area include the posterior auricular, digastric,
stylohyoid, and parotid plexus with its terminals.
 The posterior auricular nerve arises near the stylomastoid foramen and
ascends behind the ear. This branch supplies motor innervation to the
auricular and occipital muscles. The digastric and stylohoid branches
provide motor innervation to the like-named muscles as each branch
arises near that muscle.

22. muscles
 Although no muscles reside within the parotid bed,
a few are closely associated with that space.
These include the masseter, the posterior
digastric, and the stylohyoid muscles.
Ligaments
 The stylohyoid ligament, formed by a thickened
portion of the parotid fascia, helps to separate the
parotid and submandibular glands.

23.  Immediately deep to the muscles originating on the styloid process
are the last four cranial nerves, the internal carotid artery, and the
internal jugular vein.
 The glossopharyngeal, vagus, and accessory nerves exit the skull
through the jugular foramen, whereas the hypoglossal nerve exits
the skull via the hypoglossal canal. As these nerves descend to the
structures they innervate, they may be observed passing on the
lateral surface of the internal carotid artery and internal jugular vein
housed, along with the vagus nerve, in the carotid sheath.
 Within the carotid sheath, the laterally placed internal jugular vein,
originating at the jugular foramen, descends to enter the subclavian
vein at the root of the neck. The internal carotid artery ascends
within the sheath to enter the carotid canal in the petrous portion of
the temporal bone, whereas the vagus nerve descends through the
neck on its way to the thorax and abdomen.