Section 1

Chapter

1Introduction

Clinical head and neck anatomyfor the ENT anesthesiologistNicole M. Fowler and Joseph Scharpf

IntroductionAn understanding of anatomy is paramount to theability to safely anesthetize the head and neck sur-gery patient. In contrast to other patient populations,the head and neck surgery patient's pathology mayobfuscate normal anatomy and impede or even pre-vent the anesthesiologist from being able to intubatethe patient. Furthermore, recognized anatomic vari-ations may complicate the anesthesiologist's man-agement of the patient. Cooperation among theentire operating team is the key to a successful oper-ation. The surgeon and anesthesiologist must discussthe particular patient's anatomy and specific proced-ural needs prior to each case. Potential airway man-agement options such as routine oral intubation,nasotracheal intubation, awake fiberoptic intubationand even awake tracheotomy must be considered.Contemporary technological advances can enhancethis discussion by including photography and video-graphy. For example, computerized imaging systemsin use in modern operating rooms can be synchron-ized to a server in the otolaryngology clinic to allowthe review of both photographs and videos ofpatients' airways and the extent that they have beenaltered through disease progression. While the addeddimension of visual review integrated into the dis-cussion can be an invaluable adjunct to this teamapproach, always bear in mind that conditions couldhave worsened significantly since the imaging wasperformed.

Patient safety concerns continue to be increasinglyrecognized as a vital component of modern healthcare. At the authors' institution we perform both anoperative “huddle” with the patient awake and a sur-gical “time-out” prior to performing any procedure.The huddle is an ideal time to review the intubation

plan including the use or avoidance of long-actingmuscle relaxants for the case. The huddle process alsoensures that both the anesthesiologist and surgeon arepresent and ready to handle any potential periopera-tive complications. The head and neck surgeonshould be considered an airway specialist and partnerwith the anesthesiologist.

Face anatomyThe basic underlying structure of the face is formedby the skull, facial bones and mandible (Figure 1.1).The skull is formed by a series of eight bones:paired parietal and temporal bones and single frontal,occipital, sphenoid and ethmoid bones [1]. The facialskeleton creates the anterior portion of the skull andincludes the orbits, nares, maxilla and mandible. Theface is formed by 12 uniquely shaped bones: pairedlacrimal bones, nasal bones, maxillae, zygomatic andpalatine bones and a single vomer and mandible. Themaxillae and mandible support the teeth (Figure 1.1).The teeth are numbered from superior right to leftand inferior left to right from 1 to 32 for adults andlettered A–T in the same order for pediatric primarydentition. Normal occlusion, also termed classI occlusion, is defined by the mesiobuccal cusp ofthe first maxillary molar impacting the mesiobuccalgroove of the first mandibular molar [2]. Class IIocclusion, commonly referred to as retrognathic,occurs when the mesiobuccal cusp of the first maxil-lary molar impacts mesial to the groove (overbite).Class III occlusion, commonly referred to as prog-nathic, occurs when the mesiobuccal cusp of the firstmaxillary molar impacts distal to the groove(underbite).

Trauma resulting in facial fractures can compli-cate intubation. Mandibular fractures are usually

Anesthesia for Otolaryngologic Surgery, ed. Basem Abdelmalak and D. John Doyle. Published by Cambridge University Press.© Cambridge University Press 2013.

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paired and occur on opposite sides of the mandible.Fractures of the maxillae are commonly categorizedbased on the Le Fort classification [3]. Le FortI fracture is a horizontal fracture of the maxillasuperior to the alveolar process and the pterygoidplates of the sphenoid. Le Fort II fractures involvean oblique fracture of the maxillary sinus and hori-zontal fractures of the lacrimal and ethmoid bonesacross the nose resulting in an unstable midfacewhere the hard palate is separated from the skull.Le Fort III fractures involve a horizontal fracturethrough the superior orbital fissure, the ethmoidand nasal bones through the greater wing of thesphenoid bone and frontozygomatic sutures. Thismay occur in conjunction with fractures of thezygomatic arches resulting in an unstable midfacewhere the maxilla and zygomatic bones are nolonger attached to the skull. If significant facialtrauma has occurred the patient may have resultingskull and brain injuries which may supersede treat-ment of the facial injuries. Depending on the sever-ity of the trauma, the airway may have been triagedin the field and an emergency cricothyroidotomyor tracheotomy may have already been performedif an oral intubation was not possible. When

preparing to intubate a patient with a mandibularfracture carefully evaluate the teeth as the toothroots are areas of bony weakness and may beinvolved in the fracture. Orbital fractures com-monly of the inferior orbital rim may result inentrapment of the extraocular muscles; particularlythe inferior rectus can result in activation of theoculocardiac reflex [4]. This reflex between thetrigeminal and vagus nerve can result in bradycar-dia, a junctional rhythm, asystole or even death.Treatment includes surgical release of the muscle,atropine or glycopyrrolate.

Face shape is determined by the bones, musclesand subcutaneous tissue (Figure 1.2). The muscles offacial expression lie within the subcutaneous tissue.The muscles of facial expression are innervated bythe facial nerve. They generally attach to bone orfascia and act by pulling the skin to create facialexpression. When performing surgery around thefacial nerve or its branches, including otologic pro-cedures, parotidectomy, submandibular gland exci-sion and neck dissections, neuromuscular blockage iscontraindicated and all or part of the ipsilateral facemay need to be included in the surgical field formonitoring.

Perpendicular plate of ethmoid boneInferior orbital fissure

Temporal fossa

Orbital surface of frontal boneSupraorbital notch

(A)

Mental foramenAngle of mandible

Alveolar processes

Ramus

Mastoid process

Infraorbital foramen

Frontal bone

Parietal bone

Greater wing of sphenoid boneGlabella

Nasal bone

Lacrimal bone

Greater wing of sphenoid boneZygomatic boneMaxillaVomerTemporal bone

Mandible

Anterior nasal spine

Mental protuberance

Figure 1.1. Anterior cranium and overlying facial topography. Artwork created by Emily Evans.

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Ear anatomyThe ear is divided into three parts: the external,middle and internal. The external ear (Figure 1.3)includes the external auditory canal to the tympanicmembrane. This is approximately 2–3 cm in length.The lateral one-third is cartilaginous and the innertwo-thirds is composed of skin directly on the perios-teum of the tympanic portion of the temporal bone.The middle ear is an air-filled cavity containing thethree auricular ossicles – the malleus, incus, andstapes. The middle ear pressure is regulated by theeustachian tube, which opens into the nasopharynx.The inner ear is contained within the petrous portionof the temporal bone and includes the cochlea, vesti-bule and semicircular canals. The cochlear hair cellsactivate the cochlear nerve, resulting in hearing trans-mission. The vestibule is a small oval chamber

containing the saccule and utricle, which along withthe semicircular canals control balance. The labyrin-thine and tympanic portions of the facial nerve lie inclose proximity to these structures and may be dehis-cent, necessitating lack of neuromuscular blockadeand close monitoring of facial movements duringcertain otologic procedures.

Nose anatomyThe nose projects from the face largely based on theamount of cartilage. Extending from the nasal boneare the upper and lower lateral cartilages. Stability isprovided from the underlying nasal septum which isalso composed of both bone and cartilage. The pos-terior bony septum is formed from the perpendicularplate of the ethmoid and vomer but the majority ofthe septum, the anterior septum, is the quadrangular

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(B)

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Bicuspids

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Molars

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Mandible

Mandible

Figure 1.1. (cont.)

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cartilage. The nasal ala are supported by U-shapedalar cartilage which is free and mobile, allowing thedilatation or constriction of each nostril. In prepar-ation for a nasotracheal intubation or a fiberopticintubation the nares should be examined for anyseptal deviation. The degree and site of deviationmay help decide which nostril to use for the intub-ation. Care must be taken when placing any foreignobject into the nose because of its robust blood

supply. The anterior nasal septal area is referred toas Kiesselbach's plexus and is the site of a capillaryanastomosis from the sphenopalatine artery, anteriorand posterior ethmoid arteries, greater palatine arteryand the superior labial artery. Any object placed intothe nose should be directed along the floor of thenose, which is wider than the roof. In preparationfor any nasal manipulation the nasal mucosa shouldbe treated with a vasoconstrictor and anesthetic.

Orbicularis oculiOrbital part

Palpebral part

Levator labii superioris

Levator labii superiorisaleque nasii

Zygomaticus minor

Zygomaticus major

Platysma

Sternocleidomastoid

Orbicularis oris

Procerus

Depressor anguli oris Depressor labii inferioris

Frontalis

Temporalis

Nasalis

Risorius

Mentalis

Masseter

Figure 1.2. Muscles of facial expression. Artwork created by Emily Evans.

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A vasoconstrictor such as phenylephrine or oxyme-tazoline will act on the erectile tissues of the nasalmucosa and result in decongestion and openingof the nasal passages. If profuse bleeding occurspressure should be applied, and medications suchas oxymetazoline (Afrin), phenylephrine or an epi-nephrine-soaked pledget can be placed into thenares. Following successful nasotracheal intubationextreme care must be taken to position the nasotra-cheal tube such that it is not applying pressure to thenasal alar skin. Even slight pressure can result innecrosis of the alar skin. Within each nostril are thethree turbinates, inferior, middle and superior,which increase the surface area for humidificationand warming of the inspired air. The paranasalsinuses are air-filled spaces extending into thefrontal, ethmoid, sphenoid and maxillary bones.Since the advent of the endoscope much of rhinologyhas become endoscopic.

Mouth anatomyThe mouth is subdivided into the oral cavity and theoropharynx. The oral cavity begins at the skin–vermilion junction of the lips and extends posteriorlyto the junction of the hard and soft palate superiorlyand to the line of the circumvallate papillae on thetongue inferiorly. The oral cavity therefore includesthe lips, buccal mucosa, maxillary and mandibularalveolar ridges/teeth/gingival, floor of the mouth,hard palate, the retromolar trigone and the anteriororal tongue (Figure 1.4). The hard palate forms theroof of the mouth and separates the oral cavity fromthe anterior nasal vault. It is composed of the palatine

process of the maxilla and the horizontal plate of thepalatine bone. Figure 1.5 shows a rare primary palataltumor. Tumors are very friable and will bleed easilyso in this patient great care was taken to avoid anymanipulation of the palate. The retromolar trigone isa triangular area just anterior to the ascending ramusof the mandible. A triangle is drawn with its medialaspect coinciding with the anterior tonsillar pillar, thebase being across the mandibular alveolus posterior tothe last molar and its apex being the coronoid process.In this area the mucosa is tightly adherent to theascending ramus of the mandible. Carcinomas origin-ating in this region tend to invade the mandibularperiosteum and medial pterygoid muscle causing sig-nificant trimus. Referred otalgia is also a commonsymptom due to innervation by the mandibularbranch of the trigeminal nerve, the lesser palatinenerve and the glossopharyngeal nerve. Thecircumvallate papillae and terminal sulcus divide thetongue into an anterior two-thirds and posterior one-third. The anterior two-thirds of the tongue canlargely be easily visualized by the patient andclinician. Patients will routinely present with a smallnon-healing ulcer or sore lesion. The oral tongue iscomposed of three extrinsic tongue muscles: thegenioglossus, hyoglossus and styloglossus muscles(Figure 1.6; Table 1.1a). In combination with theintrinsic tongue musculature these muscles assist withspeech articulation and deglutition. The tongue mus-culature is innervated by the hypoglossal nerve(CNXII). Taste to the anterior oral tongue is suppliedby the lingual nerve (CNV3) having received fibersfrom the chorda typani nerve. As these nerve fiberstravel with those to the external ear, external auditory

Helix

Scaphoid fossa

Crura of antihelix

Antihelix

Antitragus

Triangular fossa

Tragus

Concha

Intertragic incisure

Lobule of ear

Entrance to externalauditory meatus

Figure 1.3. External ear structure.Artwork created by Emily Evans.

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canal and tympanic membrane referred otalgia is acommon presenting symptom with tongue cancers.Lateral tongue cancers drain to the ipsilateral level IBor II nodes. The medial tongue may drain directly tolevel III. The tip of the tongue drains to level IA. Thefloor of the mouth is the mucosa lying between themandibular alveolus and the oral tongue. This area is

pierced by the submandibular gland duct (Wharton'sduct) bilaterally on either side of the lingual frenulum.The length and site of attachment of the lingualfrenulum on the ventral surface of the tongue canaffect tongue protrusion. Tethering of the tongue istermed ankyloglossus and can be surgically cut if itaffects speech articulation or feeding as an infant.Odontogenic infections can become life-threateningif they spread into the submental or submandibularspaces. Ludwig's angina is a severe infection involvingthe floor of mouth. As the infection and swellingworsens the tongue is pushed posteriorly and super-iorly, causing respiratory obstruction. The patientmay have marked trismus in addition to odynophagiaand may have dysphagia to the extent that theycannot tolerate their own secretions. Infections in thisspace are considered an airway emergency and mayrequire an awake tracheotomy for management.Complete airway obstruction is the most frequentcause of death from this disease [2]. The oropharynxextends from an imaginary line extending back fromthe hard palate superiorly to the level of the hyoidbone inferiorly and includes the soft palate, tonsils,base of tongue and posterior pharyngeal wall. This

Epiglottis

Median glossoepiglottic fold

Lateral glossoepiglottic fold

Root of tongue

Body of tongue

Vallecula

Foramen cecumPalatopharyngeal arch

Palatopharyngeal muscle

Palatine tonsil

Palatoglossus muscle

Palatoglossal arch

Lingual tonsil and lingual folliclesTerminal sulcus

Vallate (circumvallate) papillae

Foliate papillae

Filiform papillae

Median sulcus

Fungiform papillae

Apex of tongue

Figure 1.4. Dorsal tongue anatomy. Artwork created by Emily Evans.

Figure 1.5. Photo of primary palatal tumor. Photo courtesy ofDr. Joseph Scharpf.

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area is much more difficult to visualize for both thepatient and the clinician. The pharyngeal walls arecomposed of mucosa, submucosa, pharyngobasilarfascia, the superior and upper middle constrictormuscle, and buccopharyngeal fascia (Figure 1.7; Table

1.1b and Table 1.2). Posterior to the buccopharyngealfascia is the retropharyngeal space. This potentialspace exists between the buccopharyngeal fascia andthe alar layer of the prevertebral fascia (Figure 1.7).This space extends from the skull base to the superior

Cartilaginous part of auditory tube(eustachian tube)

Salpingopharyngeus

Palatopharyngeus

Stylopharyngeus

Superior pharangeal constrictor

Middle pharangeal constrictor

Inferior pharangeal constrictor

Hyoid bone

Esophagus

Stylohyoid ligament

Levator veli palatini

Tensor veli palatini

PalatoglossusSoft palate

Longitudinal muscle of tongue

HyoglossusGenioglossus

Geniohyoid

Cricothyroid

Thyroid cartilage

Tracheal cartilage

Thyrohyoid membraneMylohyoid

Styloglossus

Figure 1.6. Sagittal view of the pharyngeal musculature. Artwork created by Emily Evans.

Table 1.1a. Muscles of the soft palate. Reproduced with permission from Olson TR, Pawlina W. ADAM Student Atlas of Anatomy.Cambridge University Press, 2008

Muscle Superior attachment Inferiorattachment

Innervation Main actions

Levator velipalatini

Cartilage of auditory tubeand petrous part oftemporal bone

Palatineaponeurosis

Pharyngeal br. Ofvagus n. via pharyngealplexus (CN X)

Elevates soft palate duringswallowing and yawning

Tensor velipalatini

Scaphoid fossa of medialpterygoid plate, spine ofsphenoid bone & cartilageof auditory tube

Medial pterygoid n.(a br. Of themandibular n.) viaotic ganglion (CN V3)

Tenses soft palate andopens cartilagenous part ofauditory tube duringswallowing and yawning

Palatoglossus Palatine aponeurosis Side oftongue

Pharyngeal br. Ofvagus n. (CN X) viapharyngeal plexus

Elevates posterior part oftongue and draws softpalate onto tongue

Palatopharyngeus Hard palate and palatineaponeurosis

Lateral wallof pharynx

Tenses soft palate and pullswalls of pharynx superiorly,anteriorly, and mediallyduring swallowing

Musculus uvulae Posterior nasal spine andpalatine aponeurosis

Mucosa ofuvula

Shortens uvula and pulls itsuperiorly

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Table 1.1b. Extrinsic muscles of the tongue. Reproduced with permission from Olson TR, Pawlina W. ADAM Student Atlas of Anatomy.Cambridge University Press, 2008

Muscle Stableattachment

Mobile attachment Innervation Actions

Genioglossus Sup. part ofmental spine ofmandible

Dorsum of tongueand body of hyoidbone

Hypoglossaln. CN XII

Protrudes, retracts and depressestongue; its post. part protrudestongue

Hyoglossus Body and greaterhorn of hyoidbone

Side of tongue Depresses and retracts tongue

Styloglossus Styloid processand stylohyoid lig.

Side and inf. aspectof tongue

Retracts tongue and draws it upto create a trough for swallowing

Palatoglossus Palatineaponeurosis ofsoft palate

Side of tongue Pharyngeal br. CNX and pharyngealplexus

Elevates post. part of tongue

Thyroid cartilage

Esophagus

Cricoid cartilage

Vocal folds

Sternothyroid

Anterior jugular vein

Sternohyoid

Omohyoid

Sternocleidomastoid

Anterior scalene

Middle scalene

Posterior scalene

Levator scapulae

Splenius capitis

Trapezius

Longus colliVagus nerve

Annulus fibrosus

Spinal cord

C5 vertebra

Superficial cervical fascia

Nucleus pulposus

Vertebral artery and veinLymph nodes

Internal jugular vein

Internal carotid artery

Fascial layers;

Prevertebral layerCarotid sheath

Superficial (investing) layerof deep cervical fascia

Pretracheal layerFascia of infrahyoid muscles

Figure 1.7. Divisions of the cervical fascia. Artwork created by Emily Evans.

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mediastinum. Contingent upon the patient, his or herclinical history, and the location of a retropharyngealspace abscess in relation to the great vessels (carotidartery, internal jugular vein), the abscess may beamenable to transoral drainage versus a more trad-itional transcervical drainage. The tonsils are housedwithin a fossa created by two muscles, the anteriortonsillar pillar formed from the palatoglossus muscleand the posterior tonsillar pillar by the palatopharyn-geal muscle. A small primary tonsillar or base oftongue tumor may be asymptomatic and present withmetastatic cervical lymphadenopathy. Careful exam-ination of the oral excursion is advised in any patientwith a tonsillar tumor as invasion into the lateralpterygoid muscle may result in trismus, which willnot improve with muscular relaxation. The soft palateis composed of the levator veli palatini, tensor velipalatini, musculus uvulae and tonsillar pillars musclesas above. The base of the tongue extends fromthe circumvallate papillae to the glossoepiglottic fold.The lingual tonsils are found laterally and lie in a

superficial plane creating an irregularity to thesurface. Alternatively, base of tongue tumors maygrow to very large sizes with minimal symptoms.Patients with a large base of tongue tumor may beable to maintain their airway but extreme cautionshould be taken prior to induction. An awake trache-otomy should be considered based on the anesthesiol-gist's experience and comfort with awake fiberopticintubation.

The throat or pharynx is subdivided into thelarynx and the hypopharynx. The larynx is furthersubdivided into three spaces: the supraglottis,glottis and subglottis. Furthermore the larynx is com-posed of nine cartilages joined by ligaments andmembranes: three single cartilages: thyroid, cricoidand epiglottic; and three paried cartilages: arytenoid,corniculate and cuneiform (Figure 1.8). The largest ofthe cartilages, the thyroid cartilage, was so namedfrom the Greek word thyreos, or shield, due to itsshield-like appearance and its main function beingthat of protection of the vocal cords. It is composed

Table 1.2. Pharyngeal muscles Reproduced with permission from Olson TR, Pawlina W. ADAM Student Atlas of Anatomy.Cambridge University Press, 2008

Muscle Lateral attachments Medialattachments

Innervation Main actions

Circular pharyngeal musclesSuperior constrictor Pterygoid hamulus,

pterygomandibular raphe,post. end of mylohyoid lineof mandible and side oftongue

Median raphe ofpharynx andpharyngeal tubercle

Pharyngeal and sup.laryngeal brr. ofvagus n. [CN X]through pharyngealplexus

Constrict wallof pharynxduringswallowing

Middle constrictor Stylohyoid lig. and greaterand lesser horns of hyoidbone

Median raphe ofpharynx

Inferior constrictor Oblique line of thyroidcartilage and side of cricoidcartilage

Elevatepharynx andlarynx duringswallowing,speakinga

Longitudinal pharyngeal musclesPalatopharyngeus Hard palate and palatine

aponeurosisPost. border oflamina of thyroidcartilage and sideof pharynx andesophagus

Salpingopharyngeus Cartilaginous part ofauditory tube

Blends withpalatopharynegeus

Stylopharyngeus Styloid process of temporalbone

Post. and sup.Borders of thyroidcartilage withpalatopharynegus m.

Glossopharyngealn. [CN IX]

a The salpingopharyngeus muscle also opens the auditory tube.

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of two large plate-like laminae which fuse in themidline forming a prominent V, which in men istermed the “Adam's apple”. Inferior to the thyroidis the cricoid cartilage, which is shaped as a signet ringand is the only complete cartilaginous ring in theairway. In women the cricoid cartilage is the mostprominent cartilaginous landmark. The cricothyroidmembrane bridges the gap between the thyroid andcricoid cartilages. This cricothyroid space is easilypalpable as a soft spot either inferior to the thyroidcartilage (in men) or immediately superior tothe prominent cricoid cartilage (in women). This isthe site of the most superficial aspect of thelarynx that is externally accessible. An emergencycricothyroidotomy utilizes these critical features inan airway emergency. The two cartilages articulateat the cricothyroid joint. This joint allows rotationof the thyroid cartilage, resulting in changes in thevocal cord length and tension and ultimatelychanges in vocal pitch. Posteriorly the cricoid cartil-age articulates with the arytenoid cartilage, formingthe cricoarytenoid joint, which allows the arytenoids

to move medially and laterally, as well as tilt anteri-orly and posteriorally. The vocal ligament is the skel-eton on which the vocal cords form and extends fromthe thyroid cartilage to the arytenoid cartilages. Thesupraglottis begins at the top of the epiglottis to theventricles. This includes the epiglottis (both lingualand laryngeal surfaces), arytenoids, aryepiglottic folds(AE folds) and false vocal cords. The epiglottis is aheart-shaped elastic cartilage which is pedicled offthe thyroid cartilage extending superiorly. The epi-glottis may be omega-shaped, retroflexed or floppyand may decrease the ability to visualize the vocalcords on intubation (depending on intubation tech-nique). Sensation of the supraglottis is supplied by theinternal branch of the superior laryngeal nerve. Figure1.9A is a drawing of the laryngeal complex with asupraglottic mass centered in the epiglottis. Safeintubation techniques include an awake fiberopticintubation. Figure 1.9B is a picture of an actual laryn-geal complex having been removed as a total laryn-gectomy specimen for a patient with an extensivesupraglottic tumor. The glottis includes each true

Epiglottis

Posterior arytenoid

Lamina of cricoid cartilage

Aryepiglottic muscle

Oblique arytenoid

Arytenoid cartilage

Transverse arytenoid

Epiglottis

Hyoid boneLesser horn of hyoid boneGreater horn of hyoid bone

Superior horn of thyroid cartilage

Inferior horn of thyroid cartilage

Tracheal cartilage

AnteriorPosterior

Superior

Cricothyroid

Cricoid cartilage

Thyroid cartilage

Thyroid cartilage

Cricoid cartilageCorniculate and cuneiform tubercles

Vocal foldsVestibular folds

Rima glottidis

Laryngeal prominence

Figure 1.8. Laryngeal skeleton and musculature. Artwork created by Emily Evans.

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