Head And Neck Surface Anatomy

Question 1

Carotid system

Answer 1

The cervical portion of the common carotid artery is similar on both sides­. Each lies within the carotid sheath of deep cervical fascia, together with the internal jugular vein and vagus nerve­. In the lower part of the neck, the arteries are separated by a narrow gap that contains the trachea, and higher up they are separated by the thyroid gland, larynx and pharynx­. At the level of the upper border of the thyroid cartilage (C4), the common carotid artery bifurcates into external and internal carotid arteries. The external carotid artery passes upwards
on either side of the neck, inclined at first slightly forwards and then backwards and a little laterally­. It usually gives off the ascending pharyngeal, superior thyroid, lingual, facial, occipital and posterior auricular arteries, and then enters the parotid salivary gland where it divides into its terminal branches, the superficial temporal and maxillary arteries­. The branches of the external carotid artery supply the face, scalp, tongue, upper and lower teeth and gingivae, palatine tonsil, paranasal sinuses and nasopharyngeal tube, external and middle ears,
pharynx, larynx and superior pole of the thyroid gland­. They also anastomose with branches of the internal carotid arteries on the scalp, forehead and face, in the orbit, nasopharynx and nasal cavity, and with branches of the subclavian artery in the pharynx, larynx and thyroid glands. The internal carotid artery supplies most of the ipsilateral cerebral hemisphere, eye and accessory organs, the forehead and, in part, the external nose, nasal cavity and paranasal sinuses­. It passes up the neck anterior to the transverse processes of the upper three cervical vertebrae and enters the cranial cavity via the carotid canal in the petrous part of the temporal bone­. The artery has no branches in the neck and so is easily distinguishable from the external carotid artery, should the latter require ligation, e­g­ to control haemorrhage from a penetrating injury to the neck.

Question 2

Submandibular ganglion

Answer 2

Preganglionic axons originate in the superior salivatory nucleus­. They emerge from the brainstem in the nervus intermedius and leave the main facial nerve trunk in the middle ear to join the chorda tympani, which subsequently joins the lingual nerve­. In this way, they reach the submandibular ganglion, where they synapse­. Postganglionic fibres innervate the submandibular, sublingual and lingual salivary glands; some axons presumably re-enter the lingual nerve to access the lingual glands, while others pass directly along blood vessels to enter the submandibular and sublingual glands. Some preganglionic fibres may synapse around cells in the hilum of the submandibular gland­. Stimulation of the chorda tympani dilates the arterioles in both glands, as well as having a direct secretomotor effect.

Question 3

Mandible

Answer 3

The mental tubercles are palpable on the anterior chin, and the mandibular body, alveolar processes and teeth are palpable through the cheek­. The lower border of the mandible can be traced to the angle at vertebral level C2­. The mental foramen, transmits the mental nerve and vessels. The mandibular foramen sits
on the medial surface of the ramus; a 21 mm needle is therefore sufficient to reach the foramen for dental anaesthesia. The mandibular ramus is largely covered by masseter and the parotid gland­. Movement of the condylar head at the temporomandibular joint is palpable anterior to the tragus during mouth opening/closing­. The coronoid process is palpable anterior to the condylar process through the buccal mucosa.

Question 4

Parotid gland

Answer 4

The superior border sits inferior to the zygomatic arch and passes from the mandibular condyle towards masseter­. The anterior border passes inferiorly along the posterior border of masseter, often overlying its lateral surface, then over the mandibular angle to meet the anterior border of sternocleidomastoid. The posterior border corresponds to a curve traced from the mandibular condyle to the mastoid process­. Tumours arising in this
region present with medial displacement of the soft palate and tonsil. The duct runs over masseter to its anterior border, and then bends sharply and pierces the underlying buccinator and buccal mucosa opposite maxillary tooth 7, where the duct orifice is visible and palpable­. Duct cannulation is required for sialography, ductal dilation and basket retrieval of ductal stones (sialoliths)­

Question 5

Facial nerve

Answer 5

The facial nerve may be injured in its extratemporal course as a result of facial trauma and laceration, or iatrogenically during surgery involving the parotid or submandibular glands or the temporomandibular
joint, or during facelift procedures­. The nerve exits the skull at the stylomastoid foramen and so is initially deep to the posterior margin of the external acoustic meatus.
It usually divides within the parotid gland into five main branches that radiate across the face. The temporal/frontotemporal branches emerge from the superior surface of the parotid, cross the zygomatic arch and travel towards the pterion and the superolateral brow­. The buccal branches run both above and below the parotid duct­. The marginal mandibular nerve emerges from the anteroinferior parotid and passes anteriorly­. The branches that enter the neck re-enter the face by crossing the lower border of the mandible at the anterior border of masseter and pass superficial to the facial artery and vein­. Regional incisions are therefore made at least 1­5 cm below the lower mandibular border to avoid nerve injury, which results in an upturned ipsilateral mouth via paralysis of depressor anguli oris and depressor labii inferioris.

Question 6

ANTERIOR CRANIAL FOSSA

Answer 6

The anterior cranial fossa is formed by the frontal, ethmoid and sphenoid bones, and supports the frontal lobes of the cerebral hemispheres. Its floor is composed of the orbital plate of the frontal bone.

The anterior ethmoidal nerve and vessels enter the cranial cavity where the cribriform plate meets the orbital part of the frontal bone. They then pass into the roof of the nasal cavity via a small foramen by the side of the crista galli. The posterior ethmoidal canal, which transmits the posterior ethmoidal nerve and vessels, opens at the junction of the posterolateral corner of the cribriform plate and jugum sphenoidale. The convex orbital plate of the frontal bone separates the brain from the orbit and bears impressions of cerebral gyri and small grooves
for meningeal vessels. Posteriorly, it articulates with the anterior border of the lesser wing of the sphenoid laterally and the jugum sphenoidale medially.

Question 7

MIDDLE CRANIAL FOSSA

Answer 7

The middle cranial fossa is formed by the sphenoid and temporal bones and supports the temporal lobes of the cerebral hemispheres. It is bounded in front by the posterior aspect of the lesser and greater wings of the sphenoid, behind by the superior border of the petrous part of the temporal bone, laterally by the squamous part of the temporal bone and greater wing of the sphenoid, and medially by the lateral aspect of the sphenoid body, including the carotid sulcus, sella turcica and dorsum sellae.
The middle cranial fossa communicates with the orbits by the superior orbital fissures, each bounded above by a lesser ­wing, below by a greater ­wing, and medially by the body of the sphenoid bone and
optic strut.

The body of the sphenoid bone is
deeply concave and houses the pituitary gland (hypophysis); it is therefore termed the pituitary (hypophysial) fossa, also kno­wn as the sella turcica.

Question 8

POSTERIOR CRANIAL FOSSA

Answer 8

The posterior cranial fossa is formed by the sphenoid, temporal and occipital bones, and contains the cerebellum, pons and medulla oblongata. It is bounded in front by the dorsum sellae, posterior aspects of the body of the sphenoid bone, and the basilar (or clival) part of the occipital bone; behind by the squamous part of the occipital bone; and laterally by the petrous and mastoid parts of the temporal bones and by the lateral (condylar) parts of the occipital bone.
The most prominent feature in the floor of the posterior cranial fossa is the foramen magnum in the occipital bone. The medulla oblongata exits the cranial cavity through the foramen magnum to continue as the spinal cord. The cerebellum is fully contained ­within the posterior fossa. When the lo­wer part of the cerebellum, the tonsils, descend abnormally through the foramen magnum, they may cause compression of the medulla at the level of the foramen magnum.

Question 9

Cavernous sinus

Answer 9

The cavernous sinuses are t­o large venous plexuses that lie on either side of the body of the sphenoid bone, extending from the superior orbital fissure to the apex of the petrous temporal bone. The roof of the cavernous sinus is formed by the dura lining the lo­wer margin of the anterior clinoid process anteriorly (clinoidal triangle),
and the patch of dura bet­een the anterior and posterior clinoids and the petrous apex, the oculomotor triangle.
Each sinus contains the cavernous segment of the internal carotid artery, associated ­with a perivascular sympathetic plexus. The cavernous carotid gives off t­wo major arterial branches: the meningohypophysial and inferolateral trunks.
Several cranial nerves run for­ards through the cavernous sinus to enter the orbit via the superior orbital fissure. The oculomotor and trochlear nerves and the ophthalmic division of the trigeminal nerve all lie in the lateral ­all of the sinus. The abducens nerve enters the cavernous sinus by passing belo­ the petrosphenoidal ligament ­within a dural tunnel just behind the short ascending portion of the cavernous carotid artery, and then runs on the
inferolateral side of the horizontal portion of the cavernous carotid, just medial to the ophthalmic nerve. Unlike the ophthalmic division of the trigeminal nerve, the maxillary division of the trigeminal nerve does not run through the cavernous sinus or its lateral ­all, but courses beneath the dura of the middle cranial fossa belo­w the level of the cavernous sinus.
Veins traversing the emissary sphenoidal foramen, foramen ovale and foramen lacerum may also drain into the cavernous sinus. Less frequently, the central retinal vein and frontal tributary of the middle meningeal vein also
drain into it.

Question 10

Cavernous sinus fistula and thrombosis

Answer 10

Direct communication bet­een the intracavernous portion of the internal carotid artery and the cavernous sinus, creating a caroticocavernous sinus fistula (CCF), may occur as a result of either severe head trauma or aneurysmal vessel disease. The classic signs are ptosis, proptosis (­hich may be pulsatile), chemosis, periorbital oedema, and extraocular dysmotility causing diplopia secondary to a combination of third, fourth and sixth cranial nerve palsies. Hypo- or hyperaesthesia of the ophthalmic divisions of the fifth cranial nerve and a decreased
corneal reflex may also be detected. There may be evidence of dilated, tortuous retinal veins and papilloedema. These changes can cause permanent blindness. Any spreading infection involving the upper nasal cavities, paranasal sinuses, cheek (especially near the medial canthus), upper lip, anterior nares, or even an upper incisor or canine tooth, may very rarely lead to septic thrombosis of the cavernous sinuses; infected thrombi pass from the facial vein or pterygoid venous complex into the sinus via either ophthalmic veins or emissary veins that enter the cranial cavity through the foramen ovale. This is a critical medical emergency ­with a high risk of disseminated cerebritis and cerebral venous thrombosis.