The blood supply is by the dorsal nasal artery (a terminal branch of the ophthalmic) at the root, and lower down by the external nasal artery (from the anterior ethmoidal) and by lateral nasal and septal branches of the facial artery and its superior labial branch.
Nasal cavity
The nasal cavity extends from the nares, through the external nose and between the bones of the face, as far back as the posterior nasal apertures or choanae (between the posterior borders of the medial pterygoid plates of the sphenoid and the vomer), where the nasal cavity communicates with the nasopharynx (see p. 386).
The lateral wall is formed mainly by the maxilla. But the maxilla has a large defect on its medial aspect (Fig. 6.28). Several bones contribute towards closing this defect and thereby form part of the lateral wall of the nose. The perpendicular plate of the palatine bone does so posteriorly and beyond this the medial pterygoid plate, with which it articulates, extends as far back as the choana (Fig. 6.31A). The sphenopalatine foramen at the top of the perpendicular plate provides a portal for neurovascular communication between the nasal cavity and the pterygopalatine fossa (see p. 369).
The labyrinth (lateral mass) of the ethmoid bone occupies much of the upper part of the maxillary hiatus. The inferior concha lies below it, articulating anteriorly with the maxilla and posteriorly with the palatine bone. The superior and middle conchae are part of the ethmoidal labyrinth. These conchae (traditionally, and often clinically, termed turbinates) are curved shelves of bone which project into the nasal cavity from their attachments on the lateral wall. Each partly encloses a passage, the meatus, under its concave inferior surface (Figs 6.29 and 6.30). A depression in front of the middle concha, the atrium, leads upwards into the meatus behind it. The atrium is bounded anteriorly and above by a ridge, the agger nasi, which may contain a few ethmoidal air cells. The anterosuperior part of the lateral wall is formed by the nasal bone and the frontal process of the maxilla. The lacrimal bone articulates with the latter and with the inferior concha, enclosing between them the canal for the nasolacrimal duct, which opens into the upper part of the inferior meatus about 1 cm behind the anterior end of the concha.
Figure 6.28 Left maxilla, from the medial side.
Figure 6.29 Coronal section of the nasal cavity, right orbit and maxillary sinus, from the front at the level of the second premolar tooth.
Figure 6.30 Lateral wall of the left half of the nasal cavity and nasopharynx. In the lower figure parts of the conchae have been removed to show the openings of the sinuses and the nasolacrimal duct.
The medial wall, or nasal septum, consists of bone and cartilage. The triangular vomer, articulating above with the sphenoid body, forms the posterior border of the septum (Fig. 6.31B). Inferiorly it is slotted into a grooved ridge on the hard palate and extends beyond the incisive canal. The vomer is grooved on each side by the nasopalatine nerves. The perpendicular plate of the ethmoid articulates with the upper margin of the vomer but not throughout its length. The septal cartilage, the unossified part of the ethmoid's perpendicular plate, forms the anterosuperior part of the septum. Inferiorly it is slotted into a bony groove at its vomerine and maxillary articulations. The nasal septum is frequently
deviated from the midline and small bony spurs may project from the septal surface into the nasal cavity. The anteroinferior corner of the septum is mobile, being formed by the medial crura of the paired major alar cartilages.
Figure 6.31 Skeleton of the nose: A the lateral wall of the left side of the nasal cavity. Part of the middle concha and the ethmoidal bulla have been removed to show the uncinate process of the ethmoid. There is a marker in the ostium of the sphenoidal sinus; B the nasal septum from the right.
The floor of the nose is the upper surface of the hard palate, which forms the roof of the mouth, and comprises the palatal process of the maxilla and the horizontal plate of the palatine bone. Anteriorly on either side of the septum a small opening leads to an incisive canal traversed by the nasopalatine nerve and the greater palatine artery.
The central part of the roof is the cribriform plate of the ethmoid. At the front, sloping downwards, are the nasal spine of the frontal bone and the nasal bones. At the back is the sloping anterior aspect of the sphenoid body.
The nasal cavity is piriform, or pear-shaped, broader below and narrow at the top. Nasal intubation for anaesthetic purposes is therefore more easily performed along an inferior meatus. The conchae project into the nasal cavity with increasing prominence from above downwards, so that the distances between conchae and septum are about equal. The lateral walls are roughly semicircular in shape and the nasal cavity is correspondingly tallest halfway along, where the cribiform plate forms the roof.
The surface marking of the cribiform plate is the horizontal plane on which the pupils lie as the eyes gaze directly forwards.
The skin of the external nose is reflected around the naris to line the vestibule, the part of the nasal
cavity bounded by the ala. The skin here bears stiff hairs. The mucocutaneous junction is marked by a crescentic infolding, the limen nasi, which coincides with the upper margin of the major alar cartilage. The mucous membrane lining the roof and the upper part of the septum and lateral wall (covering the superior concha but not below it) is olfactory epithelium. This is neuroepithelium containing the bipolar cells of the primary receptor neurons of the olfactory pathway; their dendrites are directed towards the nasal cavity and their axons pass up through the cribriform plate, gathered together in about 20 bundles. Olfactory mucous membrane also has supporting cells and subepithelial mucus-secreting glands. It is thicker and of a lighter (yellowish-brown) colour than the rest of the (pink) nasal mucous membrane which is respiratory in type, i.e. pseudostratified ciliated columnar epithelial cells interpersed with goblet cells. In addition there are subepithelial mucous and serous glands. Mucous secretion traps particulate matter and ciliary action wafts the mucous film back into the nasopharynx. The watery secretion of serous glands evaporates to moisten the inspired air. The mucous membrane is very vascular, with large venous sinusoids and arteriovenous shunts, especially over the inferior concha and the lower part of the septum; this helps to warm the inspired air. The mucous membrane of the nose is adherent to the underlying periosteum or perichondrium of the nasal walls, and when a submucous resection is performed surgically mucoperichondrium and mucoperiosteum are elevated before resection of septal cartilage and bone.
The sphenoethmoidal recess lies above and behind the superior concha. It receives the ostium of the sphenoidal air sinus.
The superior concha is small. It extends posteriorly from its junction with the middle concha. Its lower edge is free and overlies the superior meatus, into which drain the posterior ethmoidal air cells.
The middle concha is midway in size and position between superior and inferior. It extends back from its junction anteriorly with the superior concha. It overhangs the middle meatus, which can be seen only when the concha is displaced (Fig. 6.30). Immediately behind the posterior end of the middle concha beneath the mucous membrane is the sphenopalatine foramen. The flat area in front of the concha is the atrium of the nose.
The middle meatus presents a convex bulge beneath the concha. This is the ethmoidal bulla of the ethmoid, produced by the bulging of middle ethmoidal air cells, which open on or above the bulla (Fig. 6.30). Anterior to the bulla is a curved two-dimensional slit, the hiatus semilunaris, between the anterior surface of the bulla and the posterior edge of the uncinate process (a thin, hook-like bony leaflet which projects posteroinferiorly from the ethmoidal labyrinth; Fig. 6.31A). The hiatus semilunaris leads into the ethmoidal infundibulum, a curved cleft bordered medially by the uncinate process and laterally by the orbital plate of the ethmoid. The infundibulum extends upwards and forwards and is frequently continuous with the frontonasal recess into which the frontal sinus often opens (Fig. 6.32). The anterior ethmoidal cells open into the infundibulum or the frontonasal recess.
The maxillary sinus ostium is usually on the lateral aspect of the infundibulum between its middle and posterior third; an accessory ostium may be present anterior or posterior to the lower part of the uncinate process.
Figure 6.32 Sagittal section of the head. Plastic rods in the sphenoidal sinus, frontal sinus and nasolacrimal duct are seen entering the sphenoethmoidal recess, middle meatus and inferior meatus. The soft palate is elevated, as in the act of swallowing.
The attachment of the middle concha, referred to by rhinologists as the ground (basal) lamella of the middle turbinate, is considered to divide the ethmoidal air cells into anterior and posterior ethmoidal systems (Fig. 6.32). The anterior part of the attachment lies sagittally at the lateral edge of the cribriform plate. The middle part turns laterally across the skull base to the orbital plate where it turns inferiorly and the posterior part is attached horizontally. The area under the middle turbinate into which the maxillary sinus, frontal sinus and anterior ethmoidal system open is termed the ostiomeatal complex.
Blood supply
The main artery of the nasal cavity is the sphenopalatine branch of the maxillary artery, which enters the nose through the sphenopalatine foramen. It supplies the mucosa over the conchae and the meatuses, and also much of the septum. It anastomoses with the septal branch of the superior labial (entering through the nostril) and the ascending branch of the greater palatine (entering through the incisive canal) so forming Kiesselbach's plexus, on the lower anterior part of the septum (Little's area), a common site for epistaxis (nosebleed). Anterior and posterior ethmoidal branches of the ophthalmic artery enter the nose from the orbit and supply the roof and upper parts of the lateral wall and septum. Thus both external and internal carotid artery systems supply the nose.
Veins accompany the arteries and drain in various directions to the pterygoid plexus, facial vein and ophthalmic veins. Rarely (1%) an emissary vein may traverse the foramen caecum in front of the cribriform plate and connect nasal veins with the superior sagittal sinus.
Lymph drainage
Lymphatics drain to submandibular, retropharyngeal and deep cervical nodes.
Nerve supply
The olfactory area of the roof, and upper parts of the lateral walls and septum are supplied by the olfactory nerves.
The vestibular area is supplied by the infraorbital nerve from the face. The respiratory area of the lateral wall is supplied at the front by the anterior ethmoidal nerve (from the orbit) in the upper part, and in the lower part by filaments from the anterior superior alveolar nerve (through the wall of the
maxillary sinus); at the upper back part by the lateral posterior superior nasal branches from the pterygopalatine ganglion (through the sphenopalatine foramen); and at the lower back part by the posterior inferior nasal branches of the greater palatine nerve (through foramina in the perpendicular plate of the ethmoid bone).
The nerves supplying the septum are the olfactory in the upper part, anterior ethmoidal at the front and medial posterior superior nasal, including the nasopalatine, at the back.
Paranasal sinuses
Certain bones that form the boundaries of the nasal cavities are hollowed out. The cavities so produced, the paranasal sinuses, communicate by small apertures (ostia) with the nasal cavity. They may thus contribute to warming and humidifying inspired air. They may also allow enlargement of certain areas of the skull, thereby determining the position of the eyes and nose, while minimizing corresponding increase of bone mass.
All the sinuses are lined with respiratory mucous membrane, incorporating a sensory nerve supply;
the region of the ostium is the most sensitive part, with the main part of each sinus being relatively insensitive. The glands produce a film of mucus which is moved by the cilia in spiral fashion towards the ostium. The mucous membrane is thinner, less vascular and less adherent to adjacent periosteum than in the nasal cavity.
There are four (bilateral) sinuses. The maxillary and ethmoidal sinuses are beside the lateral walls of the nose. The frontal and sphenoidal sinuses are above and behind the nose; they abut at the midline, separated by a bony septum that is almost always off centre, causing asymmetry of these sinuses.
Maxillary sinus
The maxillary sinus is the space within the body of the maxilla, previously known as the maxillary antrum (of Highmore). The sinus is pyramidal in shape, with the apex in the zygomatic process of the maxilla and the base at the lateral wall of the nose. The roof of the sinus is the floor of the orbit. The floor of the sinus is the alveolar part (tooth-bearing area) of the maxilla; in adults it lies at a lower level than the floor of the nose. Behind the posterior wall are the infratemporal and pterygopalatine fossae. In front of the maxilla is the cheek. A ridge projecting into the cavity at the junction of roof and anterior wall is produced by the downward passage of the infraorbital nerve within its canal (Fig. 6.28).
The maxillary sinus is present at birth, but is no more than a shallow slit just beneath the medial side of the floor of the orbit. The body of the neonatal maxilla lateral to this is full of developing teeth. The sinus increases in size and after the second dentition, about the age of 8 years, the floor of the sinus is level with the floor of the nose. Rapid growth of the sinus occurs after puberty and the adult sinus varies in size; a large one may extend into the zygomatic process of the maxilla and into the alveolar process so that the roots of the molar teeth (and possibly of the premolars also) lie immediately beneath the floor or project into it. The roots are usually enclosed in a thin layer of bone; when this is absent the apex of the root is in contact with the mucous membrane. This is more likely to occur in old age, when ‘growth’ of a sinus is due to resorption of surrounding bone. Extraction of such a tooth leaves a fistula by rupture of the mucous membrane. These fistulae mostly heal spontaneously.
The ostium of the sinus is high up and well back on its nasal wall (Fig. 6.39). It is 2–4 mm in diameter. It opens at the posterior part of the infundibulum in the middle meatus of the lateral wall of the nose. An accessory ostium may open anterior or posterior to the lower part of the uncinate process (Fig. 6.30). The wall of the sinus adjacent to the ostia may only consist of mucosa and periosteum;
these areas are called fontanelles.
Blood supply is by small arteries that pierce the bone from the facial, maxillary, infraorbital and greater palatine arteries; veins accompany these vessels to the facial vein and to the pterygoid plexus.
Lymph drainage is to submandibular nodes. Nerve supply is from the infraorbital and superior alveolar (posterior, middle and anterior) branches of the maxillary nerve. These alveolar nerves run down to the teeth in the walls of the sinus, and as they do so minute branches pierce the bone to supply the mucous membrane of the sinus.
The surgical approaches for drainage of the maxillary sinus include access through the lateral wall of the nose at the inferior meatus, and through the vestibule of the mouth at the canine fossa of the maxilla. Using flexible endoscopes drainage can also be effected by increasing the size of a natural ostium. This is functionally more effective as the cilia waft secretions towards the ostium; the procedure is a part of functional endoscopic sinus surgery (FESS).
Ethmoidal sinus
Each ethmoidal sinus lies between the orbit and the nose (Fig. 6.29), in the ethmoidal labyrinth (lateral part of the ethmoid bone). The sinus is not a single cavity, being divided by bony septa into a variable number of ethmoidal air cells (sometimes themselves called sinuses). There may be only three or as many as 18, each with their own ostium, and they are called anterior, middle or posterior according to where they drain. The lateral wall of the labyrinth, in the medial wall of the orbit, is paper-thin (the lamina papyracea). The superior and middle nasal conchae project from its medial (nasal) wall. The labyrinth does not have its own roof but is closed in by the orbital part of the frontal bone (Fig. 6.39), whose medial edge articulates with the cribriform plate of the ethmoid. The anterior and posterior ethmoidal nerves pass between the roof of frontal bone and the ethmoid itself.
The anterior ethmoidal air cells occupy the anterior part of the sinus. Roofed in by the frontal bone, the bony walls are completed by the lacrimal bone. The ostia usually open into the infundibulum in the middle meatus; or else may open into the frontonasal duct (canal) that drains the frontal sinus. One or more cells may lie further forwards in the agger nasi.
The middle ethmoidal air cells also drain into the middle meatus. One or more project as a convexity into the lateral wall of the nose under cover of the middle concha, forming the ethmoidal bulla. Ostia on or above the bulla open into the middle meatus.
The anterior and middle ethmoidal air cells, situated in front of the ground lamella, of the middle turbinate are considered to constitute an anterior ethmoidal system.
At the back of the labyrinth the wall of the posterior ethmoidal air cells is completed by fusion of the orbital process of the palatine bone and the sphenoidal concha (Figs 6.25 and 6.26). The ostia of the posterior air cells open into the superior meatus. The most posterior air cell may extend far enough back to lie immediately adjacent to the optic nerve in its canal (a surgically important relationship).
Blood supply is by branches from the supraorbital, anterior and posterior ethmoidal and sphenopalatine arteries. Lymph drainage is to submandibular and retropharyngeal nodes. Nerve supply is from the supraorbital, anterior and posterior ethmoidal, lateral posterior superior nasal nerves and orbital twigs from the pterygopalatine ganglion. Hence both ophthalmic and maxillary branches of the trigeminal receive fibres from the ethmoidal sinus, with the possibility of referred pain to either branch.
Sphenoidal sinus
The pair of sphenoidal sinuses occupy the body of the sphenoid bone (Figs 6.30 and 6.26). The two are separated by a septum which is usually not in the midline, and they can vary greatly in size. When small the sinus lies in front of the pituitary fossa; as it enlarges it lies beneath the fossa and may extend back into the basiocciput. A large sinus may also extend into the greater wing of sphenoid and pterygoid process. At birth the sinuses are minute and their main development occurs after puberty.
A typical sinus is related above to the pituitary fossa and middle cranial fossa, and laterally to the cavernous sinus and internal carotid artery. Behind lie the posterior cranial fossa and pons, while below is the roof of the nasopharynx. One or both sinuses may be closely related to and even indented superolaterally by the optic canal with the optic nerve; laterally by the internal carotid artery; and inferiorly by the pterygoid canal with its nerve.
The ostium is in the anterior wall of the sinus about 1 cm above the choana, and opens into the sphenoethmoidal recess behind the superior concha (Fig. 6.32).
Blood and nerve supply is from the posterior ethmoidal artery and nerve. Lymph drainage is to retropharyngeal nodes.
Frontal sinus
The frontal sinuses are the only sinuses not present at birth; they appear during the second year as excavations into the diplöe between the outer and inner tables of the frontal bone. Each extends above the medial end of the eyebrow into the squamous part of the frontal bone and backwards into the orbital part and so into the medial part of the roof of the orbit (Figs 6.31 and 6.56). The two sinuses are unequal in extent and are separated by a bony septum in the midline region. They vary much in size and rarely may be absent. The important relations are the anterior cranial fossa and the orbit. The sinus drains through an ostium at its lower medial corner into the frontonasal duct, which opens into the middle meatus at the front end of the infundibulum (Fig. 6.32) or through anterior ethmoidal air cells.
Blood supply is by supraorbital and anterior ethmoidal arteries. Venous drainage is into superior ophthalmic veins. Lymph drainage is to submandibular nodes. Nerve supply is from the supraorbital nerves.