Nose, nasal cavity and paranasal sinuses

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CHAPTER 32 Nose, nasal cavity and paranasal sinuses

The nose is the first part of the upper respiratory tract, and is responsible for warming, humidifying, and, to some extent, filtering inspired air. It also houses the olfactory epithelium which contains olfactory receptor neurones responsible for detecting airborne odorant molecules.

The nose may be subdivided into an external nose, which opens anteriorly onto the face through the nostrils or nares, and an internal chamber, divided sagittally by a septum into right and left cavities which open posteriorly into the nasopharynx through the posterior nasal apertures or choanae. The nasal cavities are housed in a supporting framework composed of bone and fibro-elastic cartilages. The larger bones in this framework contain air-filled spaces lined with respiratory epithelium, described collectively as the paranasal sinuses. The sinuses and the nasolacrimal ducts drain into the nasal cavity via openings in its lateral walls (Fig. 32.1).

Fig. 32.1 Overview of spatial relationships between the nasal cavity, paranasal sinuses and nasolacrimal ducts.

(From Drake, Vogl and Mitchell 2005.)

EXTERNAL NOSE

The proportions of the nose and face, both from in front and the side, are of enormous significance to the rhinoplastic surgeon.

The shape of the external nose varies considerably between individuals. It is a pyramidal structure located in the midline of the midface and attached to the facial skeleton. Its upper angle or root is continuous with the forehead, and its free tip forms the apex which projects anteriorly. Its base contains two ellipsoidal apertures, the external nares or nostrils, which open onto its inferior surface, separated by the nasal septum and columella. The overall shape of the external nares is very variable. They usually measure 1.5–2 cm anteroposteriorly and 0.5–1 cm transversely and are narrower in front. The lateral surfaces of the nose unite in the median plane to form the dorsum. The alar sulcus is a groove in the skin bounding the nasal alae above and joining the nasiolabial sulcus. Below it curves towards the tip of the nose but does not reach it.

SKIN AND SOFT TISSUE

The skin and soft tissue covering the dorsum of the nose is usually thin, especially at the osseo-cartilaginous junction, and loosely connected to the nasal aponeurosis and the muscle fibres that fan out within it. Over the tip the skin is often thicker in men and has numerous large sebaceous glands but this varies considerably. These variations affect the final nasal contour and profile after nasal augmentation.

The piriform aperture has sharp edges. It is bounded below and laterally by the maxilla and above by the nasal bones (Fig. 32.2). The lateral part of the inferior edge of the piriform aperture merges into its lateral wall, which is formed by the frontal process of the maxilla. It is bounded above by the nasal part of the frontal bone and superomedially by the lateral edge of the nasal bone. The bony nasal septum articulates with the undersurface of the nasal bones and provides support to the dorsum of the nose. The nasal bones vary in thickness and width, which is of significance in planning osteotomies. They are thick and widest at the nasofrontal suture, narrow at the nasofrontal angle before they widen, and become thinner 9–12 mm below the nasofrontal angle.

Fig. 32.2 The bony and cartilaginous skeletons of the nose. A, External nose, frontal view; B, External nose, lateral view; C, Inferior view of cartilages; D, Nasal cavity, medial wall; E, Nasal cavity, lateral wall (left side).

Fractures of the nasal bones

The commonest injury of the facial skeleton is a fracture of the nasal bones. In simple fractures the break usually occurs in the frontal process of the maxilla rather than at the nasofrontal suture. The terminal branch of the anterior ethmoidal nerve and its accompanying vessels are at risk when injuries involve the dorsum of the nose

MUSCLES

The nasal muscle group includes procerus, nasalis, dilator naris anterior, depressor septi and levator labii superioris alaequae nasi (Fig. 32.3). These muscles are involved in respiration, facial expression and in the production of some sounds during speech, when their activity is dependent upon the activity of orbicularis oris and the type of sound (see Clark et al 1998). Any or all of these muscles may be absent in cleft lip deformities with corresponding functional and aesthetic consequences.

Fig. 32.3 The nasal musculature.

(From Drake, Vogl and Mitchell 2005.)

Procerus

Procerus is a small pyramidal muscle that lies close to, and is often partially blended with, the medial side of the frontal part of occipitofrontalis. It arises from a fascial aponeurosis attached to the periosteum covering the lower part of the nasal bone, the perichondrium covering the upper part of the lateral nasal cartilage and the aponeurosis of the transverse part of nasalis. It is inserted into the glabellar skin over the lower part of the forehead between the eyebrows.

Vascular supply

Procerus is supplied mainly by branches from the facial artery.

Innervation

Procerus is supplied by temporal and lower zygomatic branches from the facial nerve (a supply from the buccal branch has been described).

Actions

Procerus draws down the medial angle of the eyebrow and produces transverse wrinkles over the bridge of the nose. It is active in frowning and ‘concentration’, and helps to reduce the glare of bright sunlight.

Nasalis

Nasalis consists of transverse and alar components. The transverse part (compressor naris) is attached to the maxilla above and lateral to the incisive fossa, and lateral to the alar part. Its fibres pass upwards and medially and expand into a thin aponeurosis which merges with its counterpart across the bridge of the nose. The merged aponeuroses blend with the aponeuroses of procerus and with fibres from levator labii superioris alaequae nasi. Fibres from the transverse part may also blend with the skin of the nasolabial and alar folds. The alar part (pars alaris or dilator naris posterior) is attached to the maxilla above the lateral incisor and canine, lateral to the bony attachment of depressor septi, and medial to the transverse part, with which it partly merges. Its fibres pass upwards and anteriorly and are attached to the skin of the ala above the lateral crus of the lower lateral cartilage, and to the posterior part of the mobile septum. The pars alaris helps to produce the upper ridge of the philtrum.

Vascular supply

Nasalis is supplied by branches from the facial artery and from the infraorbital branch of the maxillary artery.

Innervation

Nasalis is supplied by the buccal branch of the facial nerve. It may also be supplied by the zygomatic branch of the facial nerve.

Actions

The transverse part compresses the nasal aperture at the junction of the vestibule and the nasal cavity. The alar parts draw the alae and posterior part of the columella downwards and laterally and so assist in widening the nares and in elongating the nose. They are active immediately before inspiration.

Dilator naris anterior

Dilator naris anterior (also known as apicis nasi or the small dilator muscle of the nose) is a very small muscle attached to the upper lateral cartilage and the alar part of nasalis, and to the caudal margin of the lateral crus and the lateral alar crus. It encircles the naris and acts as a primary dilator of the nostril.

Dilator naris anterior and the alar part of nasalis (dilator naris posterior) probably function to prevent collapse of the nasal valve during inspiration. Their EMG activity is directly proportional to ventilatory resistance and is modified by signals that travel from pulmonary mechano- and pressure receptors via afferent vagal pathways to the brainstem respiratory centre: the efferent limb of the reflex arc runs in the facial nerve.

Depressor septi

Depressor septi lies immediately deep to the mucous membrane of the upper lip. It is usually attached to the periosteum covering the maxilla above the central and lateral incisors and the anterior nasal spine, and to the fibres of orbicularis oris above the central incisor. Its fibres pass to the columella, the mobile part of the nasal septum and the base of the medial crus of the nasal cartilage. A few muscle slips may pass between the medial crura into the nasal tip. Depressor septi may be absent or rudimentary.

Vascular supply

Depressor septi is supplied by the superior labial branch of the facial artery.

Innervation

Depressor septi is innervated by the buccal branch, and sometimes by the zygomatic branch, of the facial nerve.

Actions

Depressor septi pulls the columella, the tip of the nose and the nasal septum downwards. It tenses the nasal septum at the start of nasal inspiration, and, with the alar part of nasalis, widens the nasal aperture as well as causing the nose to ‘dip’ when some people smile.

Levator labii superioris alaequae nasi

Levator labii superioris alaequae nasi arises from the upper part of the frontal process of the maxilla and, passing obliquely downwards and laterally, divides into medial and lateral slips. The medial slip blends into the perichondrium of the lateral crus of the major alar cartilage of the nose and the skin over it. The lateral slip is prolonged into the lateral part of the upper lip, where it blends with levator labii superioris and orbicularis oris. Superficial fibres of the lateral slip curve laterally across the front of levator labii superioris and attach along the floor of the dermis at the upper part of the nasolabial furrow and ridge.

Vascular supply

Levator labii superioris alaequae nasi is supplied by the facial artery and the infraorbital branch of the maxillary artery.

Innervation

Levator labii superioris alaequae nasi is innervated by zygomatic and superior buccal branches of the facial nerve.

Actions

The lateral slip raises and everts the upper lip and raises, deepens and increases the curvature of the top of the nasolabial furrow. The medial slip pulls the lateral crus superiorly, displaces the circumalar furrow laterally, and modifies its curvature: it is a dilator of the naris. Depressor septi and the medial slip of levator labii superioris alaequae nasi are sometimes described as secondary nasal dilators: there is little evidence that either of these muscles has any direct influence on the nasal valve.

Anomalous nasal muscles

Anomalous, inconstant, nasal muscles have been described. They include anomalous nasi, attached to the frontal process of the maxilla, procerus, transverse part of nasalis and the upper lateral cartilage (i.e. in a region normally devoid of muscle) and compressor narium minor, which passes between the anterior part of the lower lateral cartilage and the skin near the margins of the nares. The existence of a small levator septi nasi has been questioned.

CUTANEOUS VASCULAR SUPPLY AND LYMPHATIC DRAINAGE

Nasal skin receives its blood supply from branches of the facial, ophthalmic and infraorbital arteries. The alae and lower part of the nasal septum are supplied by lateral nasal and septal branches of the facial artery and the lateral aspects and dorsum of the nose are supplied by the dorsal nasal branch of the ophthalmic artery and the infraorbital branch of the maxillary artery. The venous networks draining the external nose do not run parallel to the arteries but correspond to arteriovenous territories of the face. The frontomedian region of the face, including the nose, drains to the facial vein, and the orbitopalpebral area of the face, including the root of the nose, drains to the ophthalmic veins. The connections of the veins of the nose, upper lip and cheek with the drainage area of the ophthalmic veins are clinically significant because they can be the route which spreads infection and initiates thrombosis of the major intracranial sinuses. Lymph drainage is primarily to the submandibular group of nodes although lymph draining from the root of the nose drains to superficial parotid nodes. There is experimental evidence that nasal lymphatics might play a major role in CSF transport in animals such as the sheep: there is currently very little evidence that a similar pathway exists in humans (but see Johnston et al 2004).

CUTANEOUS INNERVATION

Nasal skin is innervated by the infratrochlear and external nasal branches of the nasociliary nerve, and by the nasal branch of the infraorbital nerve.

NASAL CAVITY

The nasal cavity is an irregular space between the roof of the mouth and the cranial base. It is wider below than above, and widest and vertically deepest in its central region, where it is divided by a vertical osseocartilaginous septum that is approximately median in position. The bony part of the septum reaches the posterior limit of the cavity.

The nasal cavity communicates with the frontal, ethmoidal, maxillary and sphenoidal paranasal sinuses and opens into the nasopharynx through a pair of oval openings, the posterior nasal apertures or choanae. The latter are separated by the posterior border of the vomer, and each is limited above by the vaginal process of the medial pterygoid plates, laterally by the perpendicular plate of the palatine bone and the medial pterygoid plate, and below by the horizontal plate of the palatine bone (Fig. 32.4). The adult choana typically measures 2.5 cm in vertical height and 1.3 cm transversely: size is not usually affected by deviations of the nasal septum. The vomerovaginal and palatovaginal canals are found in the roof of this region.

Fig. 32.4 Posterior view of the choanae.

Each half of the nasal cavity has a roof, floor, medial (septal) and lateral walls and a vestibule.

ROOF

The roof is horizontal in its central part and slopes downwards in front and behind (Fig. 32.3). The anterior slope is formed by the nasal spine of the frontal bones and by the nasal bones. The central region is formed by the cribriform plate of the ethmoid bone which separates the nasal cavity from the floor of the anterior cranial fossa. It contains numerous small perforations which transmit the olfactory nerves and their ensheathing meningeal layers, and a separate anterior foramen which transmits the anterior ethmoidal nerve and vessels. The posterior slope is formed by the anterior aspect of the body of the sphenoid, interrupted on each side by an opening of a sphenoidal sinus, and the sphenoidal conchae or superior conchae.

FLOOR

The floor of the nasal cavity is smooth and concave transversely, and slopes up from anterior to posterior apertures. The greater part is formed by the palatine processes of the maxillae which articulate posteriorly with the horizontal plates of the palatine bones at the palatomaxillary suture. Anteriorly, near the septum, a small infundibular opening in the bone of the nasal floor leads into the incisive canals that descend to the incisive fossa: this opening is marked by a slight depression in the overlying mucosa.

The floor of the nose may be deficient as a result of congenital clefting of the hard and/or soft palate.

MEDIAL WALL

The medial wall of each nasal cavity is the nasal septum, a thin sheet of bone (posteriorly) and cartilage (anteriorly), that lies between the roof and floor of the cavity (Fig. 32.2D).

Bony septum

The septum is usually relatively featureless but sometimes exhibits ridges or bony spurs. The posterosuperior part of the septum and its posterior border are formed by the vomer, which extends from the body of the sphenoid to the hard palate (for more details, see Chapter 29). Its surface is grooved by the nasopalatine nerves and vessels. The anterosuperior part of the septum is formed by the perpendicular plate of the ethmoid which is continuous above with the cribriform plate. Other bones which make minor contributions to the septum at the upper and lower limits of the medial wall are the nasal bones and the nasal spine of the frontal bones (anterosuperior), the rostrum and crest of the sphenoid (posterosuperior), and the nasal crests of the maxilla and palatine bones (inferior).

Cartilaginous septum

The septal cartilage is almost quadrilateral and may extend back (especially in children) for some distance between the vomer and the perpendicular plate of the ethmoid. Its anterosuperior margin is connected above to the posterior border of the internasal suture, and the distal end of its superior portion is continuous with the upper lateral cartilages. The anteroinferior border is connected by fibrous tissue on each side to the medial crurae of the major alar cartilage. The posterosuperior border joins the perpendicular plate of the ethmoid, while the posteroinferior border is attached to the vomer and anterior to that to the nasal crest and anterior nasal spine of the maxilla. The anteroinferior part of the nasal septum between the nares is devoid of cartilage and is therefore called the membranous septum: it is continuous with the columella anteriorly.

Above the incisive canals, at the lower edge of the septal cartilage, a depression pointing downwards and forwards is all that remains of the nasopalatine canal which connected the nasal and buccal cavities in early fetal life. Near this recess, a minute orifice leads back into a blind tubule, 2–6 mm long, which lies on each side of the septum and houses remnants of the vomeronasal organ.

Vomeronasal organ

In most amphibia, reptiles and mammals, the vomeronasal organ is the peripheral sensory organ of the accessory olfactory system. In these animals, paired vomeronasal organs are located either at the base of the nasal septum or in the roof of the mouth, and are involved in chemical communication that often, but not exclusively, is mediated via pheromones. In many macrosomatic animals the vomeronasal organ consists of a vomeronasal duct which contains chemosensory cells, and a vomeronasal nerve which terminates in the accessory olfactory bulb in the CNS. Whether adult humans possess a vomeronasal organ remains controversial; it is claimed that the duct sometimes persists beyond the embryonic stage (for detailed reviews, see Meredith 2001, Witt & Hummel 2006) but no neural connection appears to be present in humans after birth.

LATERAL WALL

The lateral wall of the nasal cavity is formed anteroinferiorly by the maxilla and its anterior and posterior fontanelles (bony deficiencies in the medial wall of the maxilla which are obliterated to varying degrees by fibrous tissue); posteriorly by the perpendicular plate of the palatine bone; and superiorly by the labyrinth of the ethmoid bone. It contains three projections of variable size, the inferior, middle and superior nasal conchae (turbinates) (Figs 32.2E, 32.5). The conchae curve generally inferomedially, each roofing a groove, or meatus, which is open to the nasal cavity. The middle conchae may also curve inferolaterally, or may be expanded by an enclosed air cell to form a so called ‘concha bullosa’ (30% of individuals) or have a concave medial surface, known as a paradoxical turbinate (10% of individuals).

Fig. 32.5 Lateral wall of the nasal cavity. The conchae have been removed to show the positions of the ostia of the paranasal sinuses and the nasolacrimal duct.

(From Drake, Vogl and Mitchell 2005.)

Inferior concha and inferior meatus

The inferior concha is a thin, curved, independent bone (for more details, see Chapter 29). It articulates with the nasal surface of the maxilla and the perpendicular plate of the palatine bone. Its free lower border is gently curved and the subjacent inferior meatus reaches the nasal floor. The inferior meatus is the largest meatus, and it extends along almost all of the lateral nasal wall. It is deepest at the junction of its anterior and middle thirds, where it admits the inferior opening of the nasolacrimal canal (see Ch. 39). The canal is formed by the articulations between the lacrimal groove of the maxilla, the descending process of the lacrimal bone and the lacrimal process of the inferior concha. During postnatal development, the ostium of the nasolacrimal duct moves upwards and is increasingly hidden under the over-arching inferior concha.