The paranasal sinuses form developmentally through excavation of bone by air-filled sacs pneumatic diverticula from the nasal cavity. The biological role of the sinuses is debated, but a number of possible functions have been proposed. These include:. Learning Objectives Describe the structure and function of the paranasal sinuses. Key Points The sinuses are named for the facial bones that they are located behind.
There are four sinuses; the maxillary, frontal, ethmoid, and sphenoid. The other draining ostiomeatal unit, located posterior in the nasal cavity, is the sphenoethmoidal recess. It drains the posterior ethmoid sinus lateral to the superior turbinate and drains the sphenoid sinus medial to the superior turbinate [ 6 , 10 ].
Frontal recess is part of the ostiomeatal unit not shown in this coronal level, seen on more anterior view. Note the suprabullar recess on the left side black arrowheads , which is the space created above the ethmoid bulla when the roof of bulla does not reach up to the skull base, superiorly. Inferiorly, it is attached to the ethmoidal process of inferior turbinate. The anterior attachment of uncinate process is to thelacrimal bone.
Posteriorly, uncinate process forms the anteroinferior border of the hiatus semilunaris. Medial to the uncinate is the ethmoid infundibulum, and laterally is the middle meatus. The superior attachment of the uncinate process is the most interesting one, that is, because of its variability and its direct effect on frontal sinus drainage pathway. There are three patterns of attachment of the superior portion of the uncinate:.
In this case, frontal sinus drainage pathway drains into the middle meatus. Attachment to the middle turbinate: The uncinate process displaced medially by the large agger nasi air cell and attached to the middle turbinate. Frontal sinus drains into the ethmoid infundibulum with this type Figure 6B.
Attachment to the skull base: The least often site of attachment. The uncinate process extends superiorly to the skull base without contacting the agger nasi air cell. Here, frontal sinus drains into the ethmoid infundibulum as well Figure 6C. Variant attachments of the uncinate process red. A Attachment to lamina papyracea. B Attachment to middle turbinate. Frontal sinus drains into the ethmoid infundibulum.
C Attachment to skull base. Also, the frontal sinus drainage pathway ends into the ethmoid infundibulum with this type.
Pneumatized uncinate process Uncinate bulla : Literature reports a rate of about 0. If it is large enough, this could affect the patency of ostiomeatal unit [ 11 , 12 ] Figure 7. Atelectatic uncinate process: The uncinate will be adherent to the inferomedial wall of the orbit. Often seen in maxillary sinus hypoplasia or silent sinus syndrome. This condition increases the risk of inadvertent violation of the orbit during endoscopic sinus surgery.
Horizontal uncinate process: Almost always associated with large ethmoid bulla. Rarely the uncinate process could be totally absent.
Note that ostiomeatal units are patent bilaterally; however, extensive pneumatization might compromise it. The space between the anterior wall of ethmoid bulla and the free edge of uncinate process is called the hiatus semilunaris; it opens anterosuperiorly into a cavity called the ethmoid infundibulum. The ethmoid infundibulum is the space between the uncinate process and the inferomedial wall of the orbit Figure 5. Hiatus semilunaris receives drainage from the ethmoid bulla.
The maxillary sinus and often the frontal sinus, depending on the superior attachment of the uncinate process, drain into the ethmoid infundibulum. The olfactory fossa contains olfactory bulbs and blood vessels. Its boundaries are inferiorly the cribriform plate of the ethmoid and medially the crista galli.
Keros in classified the depth of olfactory fossa into three types based on the length of the lateral lamella [ 13 ]:.
Coronal view of the olfactory fossa asterisks and its variations of depth. Thick dashed line represents the cribriform plate of the ethmoid. Thin dashed lines represent the thin lateral lamella of the cribriform. The depth of the olfactory fossa classified based on the length of the lateral lamella. Type I: lateral lamella length 1—3 mm; type II: lateral lamella length 4—7 mm; and type III: lateral lamella length 8—16 mm.
Both type 1 and type 3 olfactory fossae are at increased risk for injury during endoscopic sinus surgery because in type 1 the angle between the medial and lateral lamellae of the cribriform plate is greater, and in type 3 the olfactory fossa is lower.
The nasal cavity is supplied by circulation derived from the internal and external carotid arteries, namely anterior and posterior ethmoidal arteries, sphenopalatine artery, septal branch of the superior labial artery, and the greater and ascending palatine arteries.
Sphenopalatine artery is the main supplier of the nasal cavity. In the lateral nasal wall, sphenopalatine artery after entering the nasal cavity through the sphenopalatine foramen gives off its posterior lateral nasal branches to supply the lateral wall.
And it crosses the face of sphenoid sinus toward the posterior end of nasal septum as the posterior septal artery. Veins accompany the arteries and drain to pterygoid plexus, facial vein, ophthalmic, and inferior cerebral veins [ 15 ].
Lateral nasal wall receives innervation from many nerves. Infraorbital nerves supply the vestibular area. The anterior ethmoidal nerve supplies the superior part of lateral wall. And the anterior superior alveolar nerve innervates the mucosa at the level of the wall of the maxillary sinus. The upper back mucosa is supplied by the lateral posterior superior nasal nerve. And the lower back mucosa innervated by the posterior inferior nasal nerve. The parasympathetic fibers reach the nasal cavity in the vidian nerve, and sympathetic fibers follow the blood vessels.
Lymphatic drainage of nasal cavity is to the submandibular, deep cervical, and retropharyngeal nodes. Maxillary sinus occupies the body of the maxillary bone. It is pyramidal in shape, with the base facing medially.
However, the bony defect is made much smaller by the contribution of the surrounding bones like lacrimal bone, ethmoid bone, inferior turbinate, and perpendicular plate of the palatine bone. This fontanelle is crossed by the uncinate process which divided it into a small anterior fontanelle and larger posterior fontanelle [ 16 ]. In adult individual, the maxillary sinus may extend from the area of the premolar teeth to the third molar, with a volume of approximately 15—22 ml [ 17 ]. In hyperpneumatized sinus, the apices of the molars or premolars are separated by a thin bone from the floor of the maxillary sinus or even project into the sinus floor.
Occasionally, this bone is very thin or even absent, making extraction of such a tooth risky to leave a fistula by tearing of the mucous membrane. However, these types of fistulae often end with spontaneous healing [ 18 ]. Immediately posterior to the maxillary sinus lie the infratemporal fossa laterally and the pterygopalatine fossa medially. Coronal and sagittal CT scan.
A Normal infraorbital bony canal arrows note the thin bony walls of the canal. B Bilateral aberrant locations of the infraorbital canals arrows. They are protruded into the sinus which put the nerves at risk of traumatic injury during endoscopic maxillary sinus surgery. C Sagittal view for the left maxillary sinus of same patient in B , demonstrating how the infraorbital canal is abnormally crossing the maxillary sinus small arrows.
The inferior wall of the infraorbital canal can be extremely thin, with an average thickness of 0. It can be abnormally protruded within the maxillary sinus as well [ 19 ] Figures 9B and C and In these situations, surgeon must identify these variants if present and pay extra attention during the procedure not to injure the nerve. Ostium of the maxillary sinus is located in the upper portion of the medial wall of the sinus, and it opens at the posterior end of the hiatus semilunaris below the ethmoid bulla.
The diameter of the ostium is about 2—4 mm, but it can be as wide as 10 mm. Mostly, the ostium existed as a canal with inferolateral orientation toward the sinus; however, it might be only an opening in some cases [ 20 ].
Although the development of maxillary sinus starts in the intrauterine period, at birth it is not more than a shallow sac below the medial side of the orbital floor. The growth of maxillary sinus is characterized by biphasic rapid growth, first phase during the first 3 years of life and the second phase from 7 to 12 years of age. A slow pneumatization continues until the age of 20 years as well.
By the age of nine, the floor of maxillary sinus reaches the level of the floor of nasal cavity. In adult individual, the floor of the sinus extends about 1 cm below the level of the floor of nasal cavity [ 21 ]. Accessory sinus ostium: Any maxillary sinus opening outside the hiatus semilunaris is considered an accessory ostium. It is located in the posterior fontanelle, posterior to natural ostium Figure Typically, it is smaller than the natural ostium with an average diameter of 1.
The clinical significance of the presence of an accessory ostium is that occasionally a circular flow of mucus between the natural and the accessory ostia could occur, leading to recurrent sinusitis. If an accessory ostium is encountered intraoperatively, it should be surgically connected with the natural ostium. It carries a higher risk of orbital penetration during endoscopic sinus surgery. Maxillary sinus septum: Maxillary sinus septum is defined as a ridge that is 2.
It can be bony or fibrous septum [ 23 ]. Usually extends from the infraorbital canal to the lateral wall of the sinus. Occasionally it can impair the drainage of the sinus Figure Infraorbital cell Haller cell : Any extension of the anterior ethmoid air cells along the orbital floor and lateral to the lamina papyracea is considered an infraorbital cell Figure It might compromise the patency of the maxillary ostium [ 24 ].
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