Mohamed Zaki Helal, M.D.
Professor of ORL,
Web Page: www.mzhelal.com
The nose is composed of the external nose and the nasal cavity divided into two nasal fossae by the nasal septum.
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The upper third of the external nose is bony (2 nasal bones joined in the midline), and the lower 2/3 is cartilaginous. The paired nasal bones together with the paired upper and lower lateral (alar) cartilages constitute the external framework of the nose. The columella connects the nasal tip to the upper lip separating the two nostrils. On the caudal (anteroinferior) end of the lateral side walls of external nose the “ala nasi” can be defined as a bulge forming the lateral sides of the nostrils.
The nasal cavities “fossae”, one on each sides of the nasal septum, begin at the piriform aperture and end at the choanae. Each nasal fossa is connectd with the outside through the anterior nares (nostril) and with the nasopharynx posteriorly via the choana. Apart from the nasal vestibule which is lined by stratified squamous epithelium, nasal cavity is lined by pseudostratified columner ciliated epithelium i.e. respiratory epithelium.
Each nasal fossa has four walls; roof, floor, septal wall, and lateral wall.
The roof of the nasal cavity is formed anteriorly by the nasal bones, the nasal spine of the frontal bone, and the floor of the frontal sinus. In its more horizontal midpart, the roof is formed by the cribriform plate of the ethmoid bone. Posteriorly the roof slopes down to the choana along the anterial wall of the sphenoid sinus and the body of the sphenoid bone. The cribriform plate is very thin and is penetrated by olfactory filaments carrying the meninges along with them.
The anterior three fourths of the floor of the nasal cavity are formed by the palatal process of the maxillary bone. Posteriorly, the remaining part is formed by the horizontal process of the palatine bone.
The nasal septum is formed by the quadrangular cartilage anteriorly, the perpendicular plate of ethmoid bone posterosuperiorly, the vomer bone posteroinferiorly, and the nasal crests of maxillary and palatine bones inferiorly.
It is the most complex one and is formed by the contribution of several bones: the nasal surface of the maxilla, inferior concha, superior and middle conchae of the ethmoid bone, and perpendicular plate of the palatine bone. It is related to the orbit superiorly and the maxillary sinus inferiorly. It also receives the openings of all the paranasal sinuses (PNS).
The nasal turbinates or conchae are 3 scroll-like (comma-like) projections called superior, middle and inferior. Each of them is composed of a central core of bone attached to the lateral wall and covered by mucus membrane with a submucosa rich in erectile tissue and blood sinusoids. Four spaces can be defined; three meati under the three turbinates and a spheno-ethmoid recess above and behind the superior turbinate.
1. The inferior meatus under the inferior turbinate receives the nasolacrimal duct.
2. The middle meatus lies under the middle turbinate and contains the ostia (openings) of three of paranasal sinuses forming the anterior group of paranasal sinuses. They are:
a. The frontal sinus drains at the frontal recess occupying the most anterosuperior end of the meatus and containing the superior part of the ethmoidal infundibulum (a deep crescentic 3-dimentional groove having a crescent-shaped opening called the hiatus semilunaris and a medial wall lodging the uncinate process).
b. The anterior ethmoid sinus comprises 2-8 air cells the largest of them presents a bulge named the bulla ethmoidalis. They drain into the infundibulum then into the middle meatus.
c. The maxillary sinus opens into the infundibulum anteroinferior to the bulla ethmoidalis.
3. The superior meatus covered by the superior turbinate has the ostia (1-2) of the posterior ethmoid air cells.
4. The spheno-ethmoid recess receives the sphenoid sinus ostium.
The posterior end of the middle concha points to the opening of the sphenopalatine foramen in the upper part of the vertical plate of the palatine bone.
1. Arterial blood supply: through branches of both internal and external carotid systems.
Anterior and posterior ethmoidal arteries arise from the ophthalmic artery; a branch of the internal carotid artery.
Sphenopalatine artery is a branch of the internal maxillary artery arising from the external carotid artery.
Greater palatine artery is a branch of the internal maxillary artery.
Branches from the superior labial branch of the facial artery (a branch of the external carotid) supply the anteroinferior (caudal) portion of the nasal cavity.
Little’s area is an area at the caudal end of the nasal septum about 5 mm behind the columella. A plexus of blood vessels (Kiesselbach’s plexus) is formed under the mucosa of this area. This plexus is formed by terminal branches of 4 arteries: anterior ethmoidal, septal branch of the sphenopalatine, greater palatine and septal branch of the superior labial.
2. Venous drainage: follows the feeding arteries as follows:
Anterior and posterior ethmoidal veins drain to the ophthalmic vein, sphenopalatine and greater palatine veins to the ptyregoid plexus of veins and angular vein to the facial vein.
These veins are connected to the cavernous sinus through ophthalmic vein and ptyregoid plexus. Therefore, nasal and sinus infection may cause cavernous sinus thrombophlebitis. The dangerous area of the face drained by these veins is defined as the triangle extending from the rhinion down to the lateral corners of the mouth.
3. Lymphatic drainage: The anterior part of nasal cavity drains into submental and submandibular lymph nodes, whereas, the posterior part into the retropharyngeal nodes. All of these nodes finally drain into the upper deep cervical lymph nodes.
Sensory neve supply is via branches of both ophthalmic and maxillary divisions of the trigeminal nerve.
Olfactory nerve (1st cranial nerve) carries smell sensation to the higher centers.
Autonomic nerve supply (to the blood vessels and mucous and serous glands): Sympathetic nerve fibres cause vasoconstriction and suppress glandular secretion, so, increasing nasal patency. On the other hand, parasympathetic stimulation causes vasodilatation and increases secretions.
The paranasal sinuses (PNS) are air-filled cavities inside skull bones around the nasal cavity. They communicate with the nasal cavity through small openings or ostia on the lateral nasal wall. Three pairs of large single sinuses (frontal, maxillary and sphenoid), and a fourth pair of multiple small ethmoidal air cells are present; one set on each side. According of their relation to the middle turbinate, paranasal sinuses are classified into:
Anterior Group: They drain in the middle meatus, below the middle turbinate. This group includes the frontal, maxillary and anterior ethmoid sinuses.
Frontal Sinus: lies inside the frontal bone above the orbit. A bony septum separates the two commonly unequal frontal sinuses. It is related anteriorly to the forehead, posteriorly to the anterior cranial fossa and inferiorly to the nose and orbit. It drains through an hour-glass tract “frontal recess” into or medial to the infundibulum and then into the middle meatus.
Maxillary Sinus: is the largest sinus. It lies inside the maxilla below the orbit. It is related inferiorly to the upper teeth (2nd premolar and 1st molar), medially to the nose and posteriorly to the pterygopalatine fossa. The infraorbital nerve and vessels pass through its roof and the nasolacrimal duct pass through its medial wall. It drains via an ostium into the infundibulum then into the middle meatus. The maxillary ostium lies near its roof and drainage depends on ciliary movements directed upwards towards its ostium.
Anterior Ethmoid Sinuses: The ethmoid air cells (both anterior and posterior) are 8-20 air cells occupying the ethmoid bone in between the orbit laterally and the nose medially. A thin sheet of bone ‘lamina papyracea’ separates these sinuses from the orbit. Their roof is directly related to the anterior nasal fossa. The anterior ethmoidal sinuses (2-8 cells) lay anteroinferior to the middle turbinate. Some of these cells form a bulge in the medial meatus ‘bulla ethmoidalis’. They drain through separate ostia (one for each cell) into the infundibulum and then into the middle meatus.
Posterior Group: They drain above the middle turbinate. Posterior ethmoid sinus and the sphenoid sinus are included in this group.
Posterior Ethmoid Sinuses: are located posterosuperior to the middle turbinate. They are related to the orbit and optic nerve canal, and drain via separate ostia in the superior meatus.
Sphenoid Sinus: pneumatizes the sphenoid bone. It is related laterally to the cavernous sinus, optic nerve and internal carotid artery. It is related superiorly to the pituitary gland, and inferiorly to the nasopharynx. It drains by an ostium into the spheno-ethmoid recess.