Head and Neck

PAROTID GLAND AND FACIAL NERVE (PAROTIDECTOMY)

INCISION

Perform an S-shaped preauricular incision extending from the top of the external ear to the midneck (Fig. 1.1).

OPERATIVE PROCEDURE

Elevate the skin at the subcutaneous level forward to the midcheek. Vigorous retraction with rake or self-retaining retractors is needed. Use sharp dissection to create the skin flap (Fig. 1.2). Notice that the greater auricular nerve is superficial and may be sacrificed. There are two main methods of identifying the facial nerve, anterograde or retrograde dissection. Anterograde dissection is the preferred method and is the most often used.

During anterograde dissection, the fascia is opened along the anterior border of the sternocleidomastoid muscle (SCM) and carried up along the preauricular area just anterior to the external cartilaginous canal. As the dissection proceeds deeper, medially the tragal pointer of the cartilaginous canal is identified. The facial nerve is typically 10-15 mm deep and inferior to this structure. Along the anterior border of the SCM, the posterior belly of the digastric muscle is identified. The facial nerve is 7-8 mm deep and superior to the posterior belly of digastric. In between the tragal pointer and the posterior belly of the digastric is located the tympanomastoid suture, which can be palpated. The main trunk of the facial nerve can subsequently be identified within 5 mm of the tympanomastoid suture.

Figure 1.1 Incision for parotidectomy.

Figure 1.2 Exposure of the parotid gland.
The second and less commonly used method is retrograde dissection of the facial nerve. Using this method, a branch of the nerve is identified and followed back to the main trunk. The most easily identified branches are the marginal mandibular nerve as it crosses the angle of mandible or the frontal nerve as it crosses the zygomatic arch in the superficial fascia. Once a branch is identified, it can be followed posteriorly back to the main trunk, and subsequent branches can then be dissected.

Figure 1.3 Identification of the facial nerve trunk.

Follow the facial nerve anteriorly as it enters the posterior parotid gland (Fig. 1.3). Split the parotid gland by inserting a clamp over the nerve and spreading the superficial portion out away from the deep portion of the gland (Fig. 1.4). Be sure to push the facial nerve branches flat against the deep lobe. Anteriorly, the “superficial lobe” of the parotid becomes very thin. The entire specimen is small and thin. Follow the individual branches and identify—temporal, zygomatic, buccal, marginal mandibular, and cervical. To remember these, use your hand on your ipsilateral face with your thumb as the temporal and 5th digit as your cervical branch (Fig. 1.5A).

Figure 1.4 Exposure of the facial nerve branches.

Four categories of the branching patterns of the facial nerve relative to the origin of the buccal branch are seen in this Figure 1.6.

Next, extend the cervical portion of the neck incision inferiorly along the SCM and identify the anterior track

of the marginal mandibular branch of the facial nerve by similar spreading dissection technique.

Figure 1.5 A: Branches of the facial nerve. B: Conceptual locator of the facial nerve trunk.

Figure 1.6 Branching patterns of the facial nerve.

Dissect the facial nerve anteriorly to the anterior border of the parotid gland. Identify the parotid (Stensen) duct. Return to the main facial nerve trunk. Identify the deep portion of the parotid gland medial to the facial nerve. Retract the nerve and excise the deep portion of the parotid gland. If you choose, you may now explore the posterior belly of the digastric muscle, the hypoglossal nerve, internal jugular vein, and spinal accessory nerve.

CLINICAL HIGHLIGHTS

Conceptualize facial nerve location by the following process as suggested by Beahrs. Place your fingertip on the mastoid process pointing forward. A dime-sized area deep and anterior to the fingertip will have the nerve within it (Fig. 1.5B). This method uses the tympanomastoid suture as a landmark. This line is found between the posterior bony auditory canal and the mastoid portion of the temporal bone. The facial nerve is located 6 mm deep.
The marginal mandibular branch of the facial nerve (VII) will be preserved above a transverse cervical incision made three fingerbreadths (4 cm) below the mandible. This nerve and the anterior ramus of the cervical branch supply innervation to the muscles of the corner of the mouth of the lower lip. Injury will result in persistent severe facial expressive disorder (Fig. 1.7A).
If the anterior ramus of the cervical branch is injured, minimal drooling will resolve after 4-6 months.
To Zanzibar By MotorCar: facial nerve branches. Temporal, Zygomatic, Buccal, Marginal Mandibular, Cervical. Or place your palm over your parotid and each digit will point to one branch (Fig. 1.5A).
Frey syndrome is “gustatory sweating” of the ipsilateral face after division of the auriculotemporal nerve in the distribution of the sympathetic denervation.

Figure 1.7 A: “Neural hammock” of the marginal mandibular branch (A) and anterior ramus of the cervical branch (B). B: Structures exposed after submandibular gland excision.

SUBMANDIBULAR GLAND (SUBMANDIBULAR GLAND EXCISION)

INCISION

For purposes of exposure and demonstration, the typical transverse incision performed in the OR is not used in the anatomy lab. Instead, continue the skin incision on the anterior border of the sternocleidomastoid to the suprasternal notch bilaterally. If you have used each side for the previous dissection, an anterior cervical flap will now be developed. Divide the skin from the tip of the chin in the midline down to the suprasternal notch. Each flap can now be elevated sharply deep to the platysma. This will expose the submandibular gland above the anterior and posterior bellies of the digastric muscle. In the operating room, exposure of the submandibular gland would be through an incision 4 cm below and parallel to the mandible extending deep to the platysma to preserve the marginal mandibular nerve. Skandalakis uses the term “neural hammock” to describe the innervation of the muscles of the lower lip. Neural hammock of the marginal mandibular branch (A) and anterior ramus of the cervical branch (B) are shown (Fig. 1.7A).

Figure 1.8 Submandibular gland located above the sling of the digastric muscle.

OPERATIVE PROCEDURE

Identify the submandibular gland and begin by separating the anterior border of the gland from the mylohyoid muscle (Fig. 1.8). Identify the underlying hypoglossal nerve and lingual veins. Continue deep dissection of the gland bluntly with the fingertip (Fig. 1.9). By anterior retraction, the facial artery is identified posteriorly. The submandibular duct (Wharton duct) and the lingual nerve are seen on the underlying hyoglossus
muscle. Divide the duct and vascular supply of the gland. Upon completion, review the course of the hypoglossal and lingual nerves and their position relative to the digastric muscle (Fig. 1.7).

Figure 1.9 Nerves located in the bed of the submandibular gland.

CLINICAL HIGHLIGHTS

Note that the lingual nerve may encircle the submandibular duct during its course. Injury to the lingual nerve, a branch of the trigeminal nerve V₃, VII, and IX, will cause loss of taste of the anterior two-thirds of the tongue.
Injury to the hypoglossal nerve will cause deviation of the tongue toward the injured side when the patient sticks the tongue out. The hypoglossal nerve (XII) is motor supply to the lateral tongue.
The mandibular notch is a dependable landmark to find the marginal mandibular branch of the facial nerve.
Injury to the neural hammock nerves will cause drooling involving the marginal mandibular nerve, which does not resolve, or minimal drooling involving the anterior ramus of the cervical branch resolving in 6 months.

Figure 1.10 Introducer needle position for percutaneous cricothyroidotomy.

EMERGENCY AND PERMANENT SURGICAL AIRWAYS (CRICOTHYROTOMY, TRACHEOSTOMY)

EMERGENCY CRICOTHYROTOMY

Incision

Percutaneous: A Blue Rhino or Ruesch percutaneous set will only require a small longitudinal incision at the level of the cricothyroid membrane.

Open: Open cricothyrotomy will need a 3-cm longitudinal incision above and below the level of the cricothyroid membrane. In a live patient, little bleeding will occur due to the longitudinal orientation of the neck vessels and strap muscles in the area.

Operative Procedure

Percutaneous: (Refer to the package insert for your specific percutaneous set.) Little dissection is needed. Use a Kelly, mosquito, or right-angle clamp to spread tissues in the midline. Use the introducer needle to penetrate the cricothyroid membrane and immediately angle the needle in an inferior direction in alignment with the airway (Fig. 1.10). A guide wire is inserted. Hooked
dilators are placed in size succession smallest to largest. Be sure to begin dilator insertion over the wire perpendicular to the skin. Rotate the dilator clockwise and counterclockwise to “screw” it into the airway. Do not penetrate the posterior tracheal membrane because esophageal perforation or intubation may result. Finally, place the tracheostomy, secure with twill tape around the neck, and remove the obturator.

Open: More dissection is necessary but can be done very rapidly in a clinical scenario. Use a Kelly, mosquito, or right angle clamp to spread tissues in the midline down to the cricothyroid membrane. A transverse incision in the cricothyroid membrane is made (Fig. 1.11). Place the endotracheal or tracheostomy tube into the airway under direct vision. Do not penetrate the posterior tracheal membrane because esophageal perforation or intubation may result. Secure the tube in place with a twill tape or adhesive tape.

Figure 1.11 Cricothyroidotomy incision for open emergency airway.

ELECTIVE TRACHEOSTOMY

Incision

Palpate anatomic landmarks, which include the thyroid notch, the cricoid cartilage, and the sternal notch. If no incisions have been done, perform a wide transverse “collar” incision 2 finger breadths above the sternal notch, or at the inferior border of the cricoid cartilage. The incision must be wide enough on the body to fully expose the underlying anatomy.

Operative Procedure

Create small subplatysma flaps superiorly and inferiorly. Separate the strap muscles vertically (Fig. 1.12). Define the trachea with blunt dissection. Place a tracheal hook under the cricoid cartilage and elevate the trachea superiorly. Bluntly elevate the isthmus of the thyroid gland. Divide and ligate the isthmus only if necessary for tracheal exposure. Find the 3rd tracheal
cartilage. Incise 1.5 cm of the membrane between the 2nd and 3rd cartilages transversely with a blade. Cut the 3rd cartilage longitudinally on one lateral side with a scissors. Secure the cartilage with a clamp and use your blade to cut transversely on the inferior side of the 3rd cartilage. Remove an anterior segment of the 3rd tracheal cartilage (Fig. 1.13). Place an endotracheal tube or tracheostomy tube in the airway. Do not penetrate the posterior tracheal membrane because esophageal perforation and intubation may result.

Figure 1.12 Separation of strap muscles for elective tracheostomy.

Clinical Highlights

The worst error with any of the techniques is a misplaced tube. Most commonly the tube can be misplaced in the soft tissue of the neck between the trachea and sternum. Perforation of the posterior tracheal membrane and esophageal damage or intubation can occur. Submembranous placement of the tube can occur if it is placed between the tracheal cartilage and tracheal mucosa. Having the tube in place but inadequately secured in an emergent situation may lead to a dislodged tube.

Figure 1.13 Excision of anterior segment of the third tracheal ring for tracheostomy.

Figure 1.14 Position of thyroid, parathyroids, and trachea.
Be sure to monitor O₂ saturation and/or exhaled CO₂ to ensure ventilation.
For orientation, see Figure 1.14 to see position of thyroid and parathyroid glands.

THYROID AND PARATHYROIDS (THYROIDECTOMY, PARATHYROIDECTOMY)

INCISION

The incision must be wide enough on the body to fully expose the underlying anatomy. Use the previous incisions (Fig. 1.15), which are not the “collar” incision used in the OR. Create subplatysma flaps superiorly to the thyroid cartilage and inferiorly to the sternal notch. In the OR, you will see vertical separation of the strap muscles (see Fig. 1.12). However, for purposes of exposure in the lab, divide the strap muscles transversely across the upper third of their length (Fig. 1.16). Retraction of the strap muscles laterally gives adequate exposure in the operating room, but rarely, these muscles need to be divided when a very large tumor or goiter is encountered. Remember that the innervation to the strap muscles comes in posteriorly in the lower twothirds of the muscle from ansa cervicalis branch of cervical branch of the facial nerve (see Fig. 1.6).

Figure 1.15 Incisions for head and neck exposure in the anatomy lab.

OPERATIVE PROCEDURE

Mobilize the thyroid and divide the middle thyroid veins if they still remain (Fig. 1.17). Next, identify and trace and then transect the superior thyroid artery (Fig. 1.18). Note that the external branch of the superior laryngeal nerve runs along with the superior thyroid artery and vein adjacent to the flare of the cornu of the thyroid cartilage. Note the pretracheal location of the pyramidal lobe of the thyroid and the “prelaryngeal node,” which is otherwise referred to as a Delphian node.

If possible, identify the right and left thyrocervical trunks as they branch from the subclavian arteries on each side (Fig. 1.19). Trace these vessels to the thyroid gland. Rotate the thyroid gland medially during dissection on each side. During this dissection, identify the inferior thyroid vessels and note that they are highly variable and are usually asymmetric (Fig. 1.20). Running under the inferior thyroid vessels, the recurrent laryngeal nerve becomes visible.