The larger sinus may pass across the midline and overlap the other. The inner table is a relative thin bony plate that separates frontal sinus from the anterior cranial fossa posteriorly.
On the other hand, the outer table is a considerable thick bony wall [ 36 ]. Also, these foramina act as sites of mucosal invagination within the bone, so failing to completely remove the mucosa in these sites during the sinus obliteration procedure may predispose to the development of mucocele.
The floor of each frontal sinus forms the anterior roof of the orbit. The floor consisted of a thin bone which can be eroded by the mucocele. Therefore, what lies superior to the frontal beak is frontal sinus, and what lies inferior to the beak is frontal recess [ 37 ].
The thickness of the frontal beak frontonasal process of the maxilla will determine the size and patency the frontal sinus ostium.
Parasagittal CT scan images. Superior to the beak is the frontal sinus FS. Note that the large agger nasi cell causing a significant narrowing of the frontal recess dashed line.
As agger nasi cell forms the anterior wall of the recess, ethmoid bulla EB forms the posterior wall. So, any enlargement or pathology affecting either cells could compromise the patency of the frontal recess.
Frontal recess is like an inverted funnel with its apex formed by the frontal sinus ostium. The frontal recess is not a structure by itself, rather it is formed by walls of the surrounding structures.
Boundaries of frontal recess are as follows: from the anterior and inferior side, the posterior wall of agger nasi cell; from the posterior side, the face of ethmoid bulla; lateral boundary is formed by the lamina papyracea; medial side formed by the lateral wall of olfactory fossa and the upper portion of middle turbinate; and superiorly, comes the fovea ethmoidalis. Depending on the superior attachment of the uncinate process, the frontal sinus drainage pathway drains into the middle meatus or the ethmoid infundibulum as mentioned in the uncinate process section [ 38 ].
When agger nasi cell is small, the frontal beak becomes prominent and narrows the ostium. In contrary, the large agger nasi cell results in a small frontal beak which means wider frontal sinus ostium.
However, the large agger nasi cell might compromise the frontal sinus drainage pathway at the level of frontal recess, inferiorly Figure 18B [ 39 ].
Frontoethmoidal cells Frontal cells : Classification of frontal cells was first described by Kuhn [ 40 ]. However, later Wormald modified the frontal cells classification [ 41 ]. This chapter reviews the modified classification by Wormald. They were classified into four groups as follows:. Type 1 frontal cell : Single frontal recess cell above agger nasi cell and below the frontal ostium Figure 20A. Type 2 frontal cells : Two or more cells in frontal recess above agger nasi cell and below the frontal ostium Figure 20B.
Frontal bullar cell : Single cell extends from the suprabullar region along the posterior wall of frontal recess and extends into the frontal sinus, superiorly. This differentiates it from the suprabullar cell, which does not extend into the frontal sinus. The posterior wall of the frontal bullar cell is related to anterior cranial fossa, and its anterior wall is related to frontal sinus Figure Caution must be taken during opening this cell not to cause unintentional trauma to anterior skull base.
Frontal intersinus septal cell: Occasionally, the intersinus septum is pneumatized forming an intersinus air cell, which might be communicating with either one of the frontal sinuses or could be completely an isolated air cell. It might compromise the frontal sinus ostium patency [ 42 ] Figure Coronal CT scan.
A Bilateral aplastic frontal sinuses. B Because each frontal sinus develops independently, a variant like unilateral aplastic frontal sinus can occur. Note that the posterior border of the cell is related to the anterior cranial fossa. And the frontal sinus FS is making the anterior border. The suprabullar cells SBC are limited to the frontal recess and are not extending to frontal sinus.
AN, Agger nasi; EB, ethmoid bulla. Coronal CT scan showing frontal intersinus septal air cell asterisk. Note the frontal cell type 3 on the right frontal sinus FC3.
Frontal sinus ostium might be compromised because of the impact of either of these two cells. AN, Agger nasi cell. Parasagittal CT view of the frontal recess dashed line. Expanding of any of these air cells could have an impact on the patency of the frontal recess. Also, other air cells like frontal bullar cell or frontal intersinus septal cell could compromise frontal sinus drainage pathway at the ostium level.
Frontal sinuses are the only sinuses that are not present at birth. They start pneumatization by the age of two and reach the orbital roof by the age of 5—7. By age of 12, they reach the adult size [ 3 ]. The clinical application of the frontal sinus development process is that external trephination procedure is contraindicated before the developing sinus reaches the level of orbital roof because of the risk of intracranial penetration.
Frontal sinus receives blood supply from the supratrochlear and supraorbital arteries branching from ophthalmic artery. Venous drainage is by the superior ophthalmic and diploic veins.
Lymph drainage is across the face to the submandibular nodes. Frontal sinus receives innervation from the supratrochlear and supraorbital nerves. Sphenoid sinuses occupy the body of sphenoid bone.
Typically, the ostium is located in the medial portion of sphenoidal face, about 10—12 mm superior to the upper border of the choana. The posteroinferior end the tail of superior turbinate can be used to locate the ostium, which typically would be just superomedial to the tail of superior turbinate [ 43 ]. Inferior to sphenoid natural ostium, the posterior septal artery a branch of sphenopalatine artery crosses the sphenoid face from the lateral nasal wall to the posterior end of nasal septum.
Even if it bifurcates before crossing, both branches pass inferior to the ostium. The average distance between the sphenoid ostium and the posterior septal artery or its superior branch is about 5 mm. Because of that, during widening the ostium, it is safer to dissect and widen the sphenoid ostium horizontally and superiorly. Alternatively, to use the electrocautery if the ostium will be widening more than 5 mm inferiorly [ 44 ]. Vital structures such as pituitary gland, optic nerves, cavernous sinuses and carotid arteries, maxillary divisions V2 of the trigeminal nerves within the foramina rotundum, and vidian canals are closely related to the sphenoid body.
Roof of the sinus is related to the pituitary gland and middle cranial fossa. Posteriorly lie the pons and the posterior cranial fossa. The optic nerve canal crosses the corner formed by the roof and the lateral wall on the posterior portion of the sinus on each side. On the posterolateral walls, internal carotid artery canals cavernous segment will be seen as bony prominences. Within the lateral sphenoid walls, the maxillary division of trigeminal nerves pass through the foramina rotundum toward the pterygopalatine fossae in both sides.
Coronal CT scan at the level of sphenoid sinus showing the critical structures neighboring the sinuses. In hyperpneumatized sinus, when pneumatization extends laterally between foramen rotundum and vidian canal, creating a recess known as the lateral recess asterisk.
CP, anterior clinoid process. Sphenoid sinus pneumatization: Depending on the degree of pneumatization, sphenoid sinus is classified into three types [ 45 ]. Conchal type: The degree of pneumatization is limited to the anterior portion of the sphenoid body and not reaching the level of the anterior wall of sella turcica.
Presellar type: Pneumatization extends up to the vertical level of the anterior wall of sella turcica but not beyond that. Internal carotid artery canal dehiscence: When areas of the medial side of bony canal separating the sinus from the artery are defected, putting the internal carotid artery at risk during the endoscopic sphenoid surgery. The sphenoid intersinus septum occasionally deviates off the midline and has an insertion on the internal carotid artery bony canal or the optic canal.
Excessive traction on the septum should be avoided, in these cases, not to cause avulsion of the bony wall Figure Pneumatized posterior nasal septum: Might be from an extension of air from the sphenoid sinus or crista galli. Rarely this cause narrowing of the sphenoethmoidal recess Figure Supraoptic recess and infraoptic recess: In hyperpneumatized sphenoid sinus, when pneumatization reaches superiorly and inferiorly to the optic canal, it will result in these two recesses, respectively.
In addition, pneumatization can extend from the infraoptic recess to the anterior clinoid process Figure 26A. Lateral recess: When pneumatization extensively extends inferolaterally between the maxillary V2 and vidian nerves, it creates this recess Figure Sagittal view showing the types and degree of sphenoid sinus pneumatization related to the anterior wall of sella turcica dashed line. A Conchal, when not reaching the vertical level of the anterior wall of sella turcica.
B Presellar, when reaches but not beyond it. C Sellar, pneumatization beyond the anterior wall of sella turcica. Coronal CT scan of the sphenoid sinus showing A Deviated sphenoid intersinus septum and attached to the right internal carotid artery canal arrowheads. Also, note the extension of pneumatization to the left anterior clinoid process PCP: Pneumatized clinoid process.
Right normal anterior clinoid process CP indicated for comparison. B Deviated intersphenoid septum which attached to right optic canal arrowheads. Note how thin can be the inferior bony wall of optic nerve canal, on the left side arrow. Coronal CT scan showing a pneumatized posterior nasal septum asterisk. Note the proximity of sphenoethmoid recess SER to the pneumatized portion, which can be affected in extensive pneumatization. At birth, it is not more than a small mucosal sac. Pneumatization starts around the third year of life.
It gradually progresses until it reaches the adult size around the age of Arterial supply is from the posterior ethmoidal artery and posterior septal artery. Veins drain via the posterior ethmoidal vein to the superior ophthalmic vein. The sinus mucosa receives innervation from the posterior ethmoidal nerve and the orbital branch of pterygopalatine ganglion. The Lymph drains to the retropharyngeal nodes. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.
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Built by scientists, for scientists. Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals. Downloaded: Abstract Performing a smooth and clean sinus surgery goes hand in hand with a perfect understanding of the nasal and paranasal anatomy. Keywords paranasal sinuses anatomy maxillary ethmoid frontal sphenoid endoscopic sinus surgery.
Introduction The solid knowledge of the surgical anatomy and normal development of the paranasal sinuses is the key element behind achieving superb end results, whether the target is to accomplish a therapeutic surgical procedure or to conduct a clinical trial or research. Nasal septum The nasal septum consists of three parts: 1 the cartilaginous septum quadrangular cartilage , anteriorly; 2 the bony septum posteriorly, which comprises two bones the upper one is the perpendicular plate of the ethmoid and the lower one is the vomer ; 3 the membranousseptum, which is the smallest and the most caudal part, is located between the quadrangular cartilage and the columella.
Lateral nasal wall The lateral wall of the nasal cavity is a complex structure formed by the inferior, middle, and superior turbinates and, occasionally, the supreme turbinate, the fourth turbinate. Turbinates and meatuses 3. Inferior turbinate and meatus Unlike the superior and middle turbinates, which are parts of the ethmoid bone, the inferior turbinate is an independent bone.
Middle turbinate and meatus The middle turbinate extends along the middle and posterior parts of the nasal cavity. Superior turbinate and meatus Superior turbinate occupies only the upper part of nasal cavity. Anatomical variations of the turbinates Concha bullosa: It is a pneumatization of the inferior bulbous part of middle turbinate.
Ostiomeatal unit The anterior ostiomeatal unit drains the maxillary, anterior ethmoid, and frontal sinuses. Anatomical variations of uncinate process Pneumatized uncinate process Uncinate bulla : Literature reports a rate of about 0. Hiatus semilunaris and ethmoid infundibulum 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.
Olfactory fossa The olfactory fossa contains olfactory bulbs and blood vessels. Blood supply, innervation, and lymphatic drainage of the nasal cavity 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.
Maxillary sinus natural ostium 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. Diagnostic Tests. Quality Measures. Contact Us. A maxillary sinus in each cheek Between six and 12 ethmoid sinuses on each side of the nose between the eyes A frontal sinus on each side in the forehead A pair of sphenoid sinuses behind the ethmoid sinuses Each sinus has an opening, called an ostium, which connects it to the nose.
Purposes of the Sinuses The sinuses lighten the skull or improve our voices, but their main function is to produce a mucus that moisturizes the inside of the nose. The Nose The nose and the sinuses are closely linked by the ostium.
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