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).

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.

BONE AND CARTILAGE

Bony skeleton of the external nose

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.

Cartilaginous skeleton of the external nose

The cartilaginous framework consists of the paired lateral and major cartilages and several minor alar nasal cartilages (Fig. 32.2).

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.

image

Fig. 32.3 The nasal musculature.

(From Drake, Vogl and Mitchell 2005.)

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.

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.

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.

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.

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).

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.