At the level of Osteomeatal Unit

Sub-contents:

-Scanogram, CT Coronal section, Cadaver section and representative line diagram.
- Check list.
- Surgical Importance.
Anatomy
     - Ethmoidal sinus.
     - Ethmoid roof.
     - Unciante Process.
     - Ethmoid infundibulum.
     - Middle Turbiante.
     - Ethmoid bulla.
     - Sinus Lateralis.
     -Maxillary Sinus.

Fig. 54: Scanogram at the level of Osteomeatal unit.

Fig. 55:  Coronal section in CT Scan at the level of Osteomeatal unit.

Fig. 56:  Coronal section in Cadaver at the level of Osteomeatal unit.

Fig. 57:  Representive line diagram of CT Scan at the level of Osteomeatal unit.

Fig. 58:  Correlation of CT Scan with its line representive line diagram and cadaver section at the level of Osteomeatal unit.

Top

Ethmoid sinus : (Labyrinth)

Development:

Begins : at about the fifth fetal month. By the seventh month, the different ethmoid groups are recognizable.

At birth: Completely developed in number at birth.

Develops from: several mucosal projections from the foetal nasal chamber.

Completion : Reach adult size and limit of expansion by the age of thirteenth or fourteenth year.

Pneumatization : Starts in the vertical segment and continues for one to twenty years.

Visibility : may be visible radiologically at birth. Cells are round in the newborn and they elongate toward the frontal bone by the second year. By the seventh year, the cells have gradually enlarged, reducing the intercellular septa to thin, fragile laminae of compact bone.

Anatomy:

Adult size : 3.3 x 2.7 x 1.4 cm (Average).

Chambers: The ethmoids are paired sinuses containing 5 to 15 cells per side and may vary from side to side in the same individual. The pair is held together by cribriform plate. The two laminae of cribriform plate are separate in the midline by the crista galii anteriorly and superiorly and infenorly by perpendicular piate of ethmoid bone.The ethmoid is filled with delicate septae that form the individual cells. Each cell has its own natural ostium and a well organized drainage pathway to carry mucus and debris from the sinus into the meatal drainage system.

The ground lamella of middle turbinate divides the ethmoids into two sections: anterior cells, which drain into the middle meatus, and posterior cells, which drain into the superior meatus. In sagittal plane, each ethmoid can be viewed as a trapezoid box which is narrower and taller anteriorly than posterior end (or pyramid shaped with base anteriorly).

The boundaries of ethmoid are (Fig):

Roof: Medial extension of the frontal bone anteriorly and a small portion posteriorly by the planum phenoidale of the sphenoid bone.

Lateral Wall: Anteriorly lacrimal bone, lamina papyracea in the middle and sphenoid bone in optic canal region.

Posterior: The sphenoid bone forms the posterior wall of the box as the common wall between the sphenoid sinus and the posterior ethmoid cells.

Anteriorly:Anterior wall of anterior ethmoid cells.

Medially :Middle, superior and sometimes supreme turbinates.

Ethmoid cells have great tendency to encroach upon adjacent structures. This encroachment may be:

I. Intramural   

        - Invasion of the bulla by the anterior ethmoid group of cells.

        - Invasion of posterior area by the bullar cells, causing flattening of the posterior cells.

II. Extramural cells

- Ethmoid cells can grow in any and all directions until they encounter hard bone and give rise to following variants:.

      - Supra-orbital cell (15%) :Pneumatization of the supra-orbital plate of frontal bone (Fig).

      - Frontal bulla : Encroachment on the floor of the frontal sinus.

Fig. 59:  Coronal Section: Showing Frontal Bulla (White arrow) .

      - Pneumatization of the crista galli.

Fig. 60:  Coronal Section: Showing Pneumatizaiton of the Crista Galli (Black arrow) .

     - Pneumatization of the uncinate process.

Fig. 61:  Coronal Section: Showing Pneumatizaiton of the Uncianate Process (Black arrow) .

      - Concha bullosa.

Fig. 62:  Coronal Section: Bilateral Concha bullosa have laterized the uncinate process and narrowed ethmoid infundibulum on both sides (Black arrow) .

      - Pneumatization of the septum which may even pass through the nasal septum to the other side.

      -Haller's cell: Invasion of infra-orbital plate of the maxilla.

Fig.63 : Coronal Section:  Haller's cell: Invasion of infra-orbital plate of the maxilla (Gray Arrow). CB: Concha bullosa, MS: Maxillary Sinus and Uncinate Process (White arrow).

      - Onodi cells : Sphenoethmoid cells.

Fig. 64 : Sphenoethmoid cell:Invasion of the Sphenoid cell give rise to Sphenoethmoid cell or Onodi cell (White arrow) which is in contact with the Optic nerve (Black arrow).

Top

Ethmoid Roof:

Fig. 65 : Coronal section: Enlarged view: Shwoing ethmoid roof.

The anterior two-thirds of ethmoid roof is formed by thick and dense orbital plate of the frontal bone, the fovea ethmoidalis. Average thickness is 0.5 mm. It slants posteriorly at a 15 degree angle. Medially it joins the lateral lamella of cribriform plate and laterally joins the lamina papyracea. The lateral lamella of the cribriform plate forms a very fragile junction laterally with lateral border of the olfactory fossa and medially with dome of the ethmoid. It is only one-tenth as strong as the roof, the height and shape varying considerably from case to case and even from one side to the other. It can be as high as 15 to 17 mm above the cribriform plate. The medial slope of the roof also varies on both sides.

Height of the ethmoid roof: Kero's Classification:

Keros has differentiated the ethmoid roof configuration into three types based on the length of the lateral lamella of the cribriform plate. See Fig. 62,63 & 64.

Type I : Length of the lateral lamella: 1 - 3 mm. Fig.

Fig.66 :  Coronal Section: Kero's type I Ethmoid Roof where the height of the lateral lamella of the Cribriform plate is 1 - 3 mm deep.

Type II: Length of the lateral lamella: 4 - 7 mm. Fig.

Fig.67:  Coronal Section: Kero's type II Ethmoid Roof where the height of the lateral lamella of the Cribriform plate is 4 - 7 mm deep.

Type III: Length of the lateral lamella: 8 - 17 mm. Fig.

Fig. 68:  Coronal Section: Kero's type II Ethmoid Roof where the height of the lateral lamella of the Cribriform plate is 4 - 7 mm deep.

Foveal place measurement:

Height of the fovea can also be measured using foveal plane and the foveal angle (Robert M Meyers et al)

Foveal plane is a horizontal plane passing through the juction of the fovea with the medial orbital walls.

- High foveal plane: Foveal plane passing through the upper one third of the orbit (Fig).

Fig. 69:  Coronal Section: Showing high Foveal Plane.

- Mid foveal plane: Foveal plane passing through the middle portion of the orbit.

Fig. 70:  Coronal Section: Showing high Foveal Plane.

- Low foveal plane: Foveal plane lying below the mid-orbital plane (Fig).

Foveal angle is the angle between the fovea and the lamina papyracea : A low sloping fovea predisposes to anterior cranial penetration and it is often quite thin in contrast to the thickness of its normal state.

Fig. 71:  Coronal Section: Showing high or shallow foveal angle.

Fig. 72:  Coronal Section: Showing low or deep foveal angle.

Height of skull base at posterior ethmoidal cells:

Height of skull base at posterior ethmoidal cells level is measured as the distance between the roof of the maxillary sinus and the skull base.

Fig. 73:  Coronal Section: Showing height of the skull base at posterior ethmoidal cells.

Top

Uncinate Process

The uncinate process is a thin, sagittaly oriented bony leaflet that runs in a sickle-shaped curve from its anterosuperior end to posteroinferiorly. It resembles a slightly bent hook or a boomerang. Its posterior margin is sharp, concave, and lies roughly parallel to the anterior surface of the ethmoid bulla, located just behind it. The uncinate process has three layers: the inner mucosal layer, the middle bony layer and the outer mucosal layer. The inner mucosal layer is also the medial mucosal wall of the infundibulum. The attachments of uncinate process are:

Anterior: The ascending, anterior convex margin of the uncinate process is in contact with the bony lateral nasal wall, and can extend as far as the lacrimal bone, thus forming inferomedial wall of agger cell.

Inferior: Ethmoidal process of inferior turbinate and the perpendicular plate of the palatine bone.

Posterior: Posterior free margin is concave and runs parallel to the curvature of the bulla ethmoidalis and does not fuse with any other structure.

Superior: May attach to the lacrimal bone. This uppersegment of the uncinate process runs a variable course and is hidden by the insertion of the middle turbinate. The uppermost portion may be attached to the base of the skull or the lamina papyracea or it may fuse with the middle turbinate anterosuperiorly.

Between the posterior free margin and the anterior surface of the ethmoidal bulla is a sickle-shaped cleft, called the hiatus semilunaris.

Through the hiatus semilunaris, a path leads anteriorly into a three-dimensional space, lateral to the uncinate process, called the ethmoidal infundibulum. The distance between the posterior free margin of the uncinate process and the lamina papyracea varies between 1.5 and 5 mm.

Variations : The uncinate process may show a large number of anatomic variations:

1. Medially bent or curved uncinate process: The most common and pathologically significant variation (Fig).

Fig.74:  Coronal Section: Medially bent or curved uncinate process (White arrow).

2. Laterally bent (atelectatic) Uncinate Process: Lateral bend of uncinate process to various extents can narrow the ethmoid infundibulum. A concha bullosa, paradoxical middle turbinate or disease process can push the uncinate process laterally, narrowing the infundibulum.

Fig.75:  Coronal Section: Laterally bent (atelectatic) Uncinate Process (White arrow).

3. Elongated or Enlarged uncinate processes: The uncinate process may extend too far posteriorly, impinging its free posterior margin onto the ethmoid bulla, thereby significantly narrowing the hiatus semilunaris.

Fig.76:  Coronal Section: Elongated or Enlarged uncinate processes (White arrow).

5. Horizontally oriented uncinate process.

Fig.77:  Coronal Section: Elongated or Enlarged uncinate processes (White arrow).

6. Pneumatized uncinate process.

Fig.78:  Coronal Section: Bilateral pneumatized uncinate processes (White arrow).

7. Pathologic or secondary changes in Uncinate process: The bony plate of uncinate process may become demineralized in chronic polyposis or other inflammatory diseases making it invisible on radiographs.

Fig.78:  Coronal Section: Showing Pathologic or secondary changes in Uncinate Process.

8. Mucosa over the uncinate process may be polypoidal or sometimes there may be perforation in the uncinate process due to chronic inflammatory conditions.

Fig.79:  Coronal Section: Showing Polypoidal changes of mucosa over the Uncinate Process.

Top

Ethmoid Infundibulum

A well defined, three dimensional cleft of the anterior ethmoids, located in the anteroinferior segment of the hiatus semilunaris with following boundaries:

Medially: uncinate process.

Laterally: mainly by the lamina papyracea with the frontal process of the maxilla and occasionally by the lacrimal bone in the anterosuperior region Anteriorly: it ends in a sharp angle at the line of attachment of uncinate process to the lamina papyracea and therefore it appears in V-shape in axial sections.

Posteriorly: anterior surface of the ethmoid bulla, infront of which the infundibulum opens into the middle meatus through the hiatus semilunaris.

Superiorly: the relationship of the infundibulum to the frontal recess varies depending on the superior attachment of the uncinate process.

If the uncinate process is attached to lamina papyracea, the ethmoidal infundibulum is closed superiorly by a blind pouch called the recessus terminalis and the frontal recess opens into the middle meatus medial to the infundibulum between the uncinate process and the middle turbinate. If the uncinate process is attached to the skull base or middle turbinate, the frontal recess opens into the infundibulum.

Fig.80 :  Coronal Section: Ethmoid Infundibulum: Average depth is 2 mm, B: Bulla Ethmoidalis, EI: Ethmoid Infundibulum,     U: Unciante Process, MS: Maxillary Sinusitis.

Fig. 81: Axial Section: Picture showing Ethmoid Infundibulum. U: Uncinate process, B: Bulla Ethmoidalis, EI: Ethmoid infundibulum and MS: Maxillary Sinus.

Fig. 82: Axial Section: Picture showing Ethmoid Infundibulum. U: Uncinate process, B: Bulla Ethmoidalis, EI: Ethmoid infundibulum and MS: Maxillary Sinus.

Variations:

- Deep and narrow infundibulum : The wall of the uncinate process is more than 2 mm high (25%-cases Van alyea).

- Shallow and wide infundibulum : The wall of the uncinate process is less than 2mm high (5%)

- Overhanging bulla with deep and narrow infundibulum : The tall uncinate process hugs the bulla, making the infundibulum a long, narrow channel.

Fig.83:  Coronal Section: Large bulla with disease process pushing the middle ear medial and horizontally. Ethmoid infundibulum is blocked. B: Bulla, EI: Ethmoid Infundibulum, MS: Maxillary Sinus, U: Uncinate Process.

- Overhanging Haller's cell with deep and narrow infundibulum: The tall uncinate process hugs the Haller's cell and the bulla, making the infundibulum a long narrow channel.

Fig. 84:  Coronal Section: Large Concha bullosa as well as Bulla ethmoidalis narrowing the ethmoid infundulum. BE: Bulla ethmoidalis, CB: Concha Bullosa, BE: Bullar ethmoidalis, EI: Ethmoid infundulum and MS: Maxillary Sinus.

Fig. 85:  Coronal Section: Haller cells narrowing the ethmoid infundulum. EI: Ethmoid infundibulum, MS: Maxillary sinus & U: Uncinate Process.

-Giant Haller's cell with shallow infundibulum.

Presence of Concha bullosa, paradoxical middle turbinate and pathological process like polyps can push the uncinate medially narrowing the infundibulum.

Fig. 86:  Coronal Section: Bilateral Concha Bullosa have pushed the uncinate process medially and narrowed the ethmoid infundibulum. CB: Concha bullosa, U: Unciante process, EI: Ethmoid infundibulum and MS: Maxillary sinus.

Fig. 87:  Coronal Section: (R) Concha bullsa and (L) Paradoxial middle turbinate narrowing the ehtmoid infundibulum. CB: Concha bullosa, PMT: Paradoxical middle turbiante, U: Uncinate process and EI: Ethmoid infundibulum.

Fig.88:  Coronal Section: Uncinate process blocking the ethmoid infundibulum. EI: Ethmoid infundibulum and U: Uncinate Process.

Top

Middle turbinate

Middle tubinate originates from the third basal lamella of the ethmoturbinalis. The basal lamella of the turbinate divides ethmoid complex into anterior and posterior groups and its position varies depending on the pneumatization of the anterior and posterior ethmoid cells. The insertion of the middle turbinate can be divided into three parts (Fig86-88). These attachments provide stability to middle turbinate. Superior meatus may extend into the bony lamella of the middle turbinate producing interlamellar cell and/or concha bullosa.

Fig.90:  Coronal Section: Part I or Vertical Part: Anterior 1/3rd of the middle turbinate lies in sagittal plane. Middle turbinate attachment to the junction of the cribroform plate and lamina laterlais is seen in this picture. CP: Cribroform plate, LL: Lateral lamella,J: Junction of Cribriform plate wiht lateral lamella, MT: Middle turbinate, IT: Inferior turbinate, CG: Crista galli, and MS: Maxillary sinus.

Fig. 91:   Coronal Section: Part II or Oblique Part: Middle 1/3rd of the middle turbinate lies in Horizontal plane. Attachment of Basal lamella to lamina papyracea is seen here. BL: Basal lamella, LP: Lamina Papyracea, B: Bulla ethmoidalis, MT: Middle turbiante, UP: Uncinate process.

Fig. 92: Coronal Section: Part III or Horizontal Part: Posterior 1/3rd of the middle turbinate lies in Horizontal plane. Attachment of the middle turbinate to perpendicular plate of ethmoid is seen here. PE: Posterior ethmoids, MT: Middle turbinate, PPE: Perpendicular plate of palatine bone, IT: Inferior turbinate, MS: Maxillary sinus.

Concha Bullosa : Is an aerated middle turbinate that could compress the uncinate process and obstruct the middle meatus and infundibulum. Present in 35% of the population The degree of pneumatization vary not only from person to person, but also from side to side. Usually one cell and occasionally two to three cells may be seen. Orgination of the pneumatization may be from frontal recess, agger nasi, lateral sinus or middle meatus.

Fig.93: Bilateral Concha Bullosa: Bilateral concha bullosaare narrowing the ethmoid infundibulum. CB: Conchal bullosa, UP: Uncinate Process, EI: Ethmoid Infundibulum, MS: Maxillary sinus.

Fig. 94:  Axial Section: Showing small concha on (L) Side. MT: Middle turbinate, U:Uncinate process, EI: Ethmoid Infundibulum, B: Bulla Ethmoidalis.

Fig. 95:  Axial Section: (R) Concha bullosa showing 2 cells.

Fig.96:  Coronal Section: Large Concha Bullosa. EI: Ethmoid infundibulum, UP: Uncinate process and MS: Maxillary Sinus.

Fig. 97:  Coronal Section: Showing Bilateral concha bullosa (CB).

Fig. 98:  Coronal Section: Bilateral concha bullosa. Large concha have laterized the uncinate process and narrowed the ethmoid infundibulum.

Interlamellar cell : Pneumatized cell in the lamella of the middle turbinate. Pneumatization originates from the superior meatus

Fig. 99 : Coronal Section: Showing an Inter-lamellar cell.

Paradoxic middle turbinate :Middle turbinates that are oriented convex to the lateral wall of the nasal cavity rather than assuming the usual concave orientation. It may compress the uncinate process and obstruct the osteomeatal unit. Overall incidence is 10%. Frequently seen in association with hypoplastic maxillary sinus.

Fig. 100:  Coronal Section: (R) Concha bullosa and (L) Paraodoxic middle turbiante. CB: Concha bullosa and PMT: Paradoxic middle turbinate.

Enlarged and anterior extending middle turbinate :Middle turbinate can extend more than 1 cm beyond its attachment, overlapping the uncinate process and agger nasi cells.

Fig. 101: Axial Section: Anteriorly extending middle turbinate on (L) side. MT: Middle turbinate, NLD: Nasolacrimal duct, B: Ethmoid Bulla and MS: Maxillary sinus.

Pneumatized superior turbinate : Is rare and may force the superior turbinate anteriorly between the middle turbinate and the septum causing headache, nasal obstruction and anosmia. Usually bilateral.

Fig. 102:  Coronal Section: Pneumatized Superior turbinate. ST: Superior turbinates, PE: Posterior ethmoids, MT: Middle turbinates, IT: Inferior turbinates and MS: Maxillary sinus.

Turbinate sinus : Exaggerated normal lateral curve of the middle turbinate may envelope the middle meatus. The space under the concavity of the such middle turbinate which is frequently filled by a large ethmoidal bulla is often called as turbinate sinus.

Fig. 103:  Coronal Section: Turbinate sinus: B: Bulla and TS: Turbianate sinus and MT: Middle turbinate.

Top

Ethmoid Bulla

The ethmoid bulla, generally the largest air cell in the anterior ethmoid forms the most constant landmark. It is created by the pneumatization of the bulla lamella. Minimal or no pneumatization seen in 8% of cases. Rarely absent. A bony ridge or bulge, the torus lateralis, occurs in 40% of cases.

The boundaries are:

Anterior: Convex curvature is parallel to the posterior free border of the uncinate process. Superiorly anterior bullar wall forms the posterior wall of the frontal recess. This wall may be vestigial or completely absent, in which case there is a direct communication between the frontal recess and the sinus lateralis.

Superior: Fovea and sinus lateralis, if present. When sinus lateralis is well formed the bulla and frontal recess drain into it.

Posterior: Basal lamella, for a varied distance.

Lateral: Lamina papyracea.

Medial: Covered by the middle turbinate.

Fig.104 : Axial Section : Showing boundaries of Bulla ethmoidalis. B: Bulla ethmoidalis, U: Uncinate Process, HS: Hiatus semilunaris, MT: Middle turbinate, EI: Ethmoid infundibulum and MS: Maxillary sinus.

Fig. 105:  Axial Section : Enlarged view: Showing boundaries of Bulla ethmoidalis. B: Bulla ethmoidalis, U: Uncinate Process, HS: Hiatus semilunaris, MT: Middle turbinate, NS: Nasal septum, SL: Sinus lateralis, LP: Lamina Papyracea, EI: Ethmoid infundibulum and MS: Maxillary sinus.

Fig. 106:  Axial Section : Enlarged view: Showing boundaries of Bulla ethmoidalis. B: Bulla ethmoidalis, U: Uncinate Process, HS: Hiatus semilunaris, MT: Middle turbinate, NS: Nasal septum, SL: Sinus lateralis, LP: Lamina Papyracea, EI: Ethmoid infundibulum and MS: Maxillary sinus.

Fig. 107:  Axial Section: Showing bulla with multiple cells. B: Bulla ethmoidalis, MT: Middle turbinate, U: Uncinate process, NLD: Nasolacrimal duct and MS: Maxillary Sinus.

Fig. 108:  Coronal Section: Showing Bulla ethmoidalis with multiple cess: B: Bulla ethmoidalis, LP: Lamina papyracea, MT: Middle turbinate, U: Uncinate process, EI: Ethmoid infundibulum, HS: Hiatus Semilunaris, IT: Inferior Turbinate and MS: Maxillary Sinus.

Fig. 109:  Coronal Section: Showing a small bulla with single cell.

Variations of Bulla Ethmoidalis: The extent of pneumatization (Fig. 96-100) of the ethmoidal bulla is variable. When extensively pneumatized, the ethmoid bulla can fill the middle meatus like a balloon. An excessively pneumatized bulla may expand:

Anteriorly: Large bulla can come into intimate contact with the posterior free margin of the uncinate process and thereby blocking the hiatus semilunaris.

- A large bulla can extend so far anteriorly that the bulla forces its way between the uncinate process and the head of the middle turbinate. Endoscopically which may give an appearance of double middle turbinate.

Fig.110:  Coronal Section: Large bulla with disease process pushing the middle ear medial and horizontally. Ethmoid infundibulum is blocked. B: Bulla, EI: Ethmoid Infundibulum, MS: Maxillary Sinus, U: Uncinate Process.

Medially: May extend Beyond the hiatus semilunaris and block it or form an extensive area of surface contact with the lateral mucosal surface of the middle turbinate (the "turbinate sinus"). This is one of the most common sites from which nasal polyps originate.

Posteriorly: Ethmoidal bulla may fuse with the ground lamella of the middle turbinate over a variable distance.

Top

Sinus lateralis

Sinus lateralis or lateral sinus of Grunwald (Fig, 102 & 103), also known as suprabullar recess or retrobullar recess is not a constant feature. It is a two dimensional space bounded:

Laterally: by lamina papyracea.

Superiorly: roof of the ethmoid (fovea).

Posteriorly: ground lamella of the middle turbinate.

Anteriorly and inferiorly: roof and posteriorwall of the ethmoid bulla.

Medially: Middle turbinate.

Fig. 111:  Coronal Section: Enlarged:  SL: Sinus lateralis, HSS: Hiatus semilunaris, BL: Basal lamella, LP: Lamina papyracea,    B: Bulla ethmoidalis and EI: Ethmoid infundibulum.

Fig. 112:  Sagittal Section: SL: Sinus Lateralis, B: Bulla ethmoidalis, and FS: Frontal sinus.

Dorsally a lateral sinus can extend far posteriorly and inferiorly between ethmoidal bulla and the ground lamella of the middle turbinate. It opens between bulla ethmoidalis and the basal lamella in a space known as the "hiatus semilunaris superior" When lateral sinus is well pneumatized ethmoid bulla usually opens into it. If the bulla lamella is not completely developed, the lateral sinus may continue anteriorly into the frontal recess. Endoscopically, the lateral sinus can be reached through the superior hiatus semilunaris medially between the ethmoidal bulla and the middle turbinate and it appears as a sickle shaped cleft.

Top

Maxillary Sinus: (Antrum of Highmore)

Development: Begins: in 3rd fetal month.

At birth: Present.

Develops from :an invagination of the nasal mucous membrane into the maxillary bone.

Pneumatization : starts at birth.

Growth: continues upto 18 years of age.

Adult size (Average):

Height: 33 mm.

Width: 23 mm.

Depth: 34 mm

Chambers : Usually, one on each side. Two or more chambers may be present on one or both sides (1- 6 %). Asymmetry and unilateral hypoplasia can occur, but complete aplasia is rare. There may be thin bony intrasinus septa, complete or incomplete.

The location of maxillary ostium, high in the infundibulum and its intimate relationship with the molar teeth makes it more prone to infections.

Relations:

Anteriorly: Infraorbital nerve in infraorbital foramen located in its midsuperior part, below the orbital rim. Infraorbital nerve passes through it.

Inferior: margin is indented by teeth. The canine fossa i.e., the partabove the canine tooth is thin.

Posteriorly: Thicker laterally than medially. Behind this wall is the pterygomaxillary fossa and its content: internal maxillary artery and its branches, sphenopalatine ganglion and the vidian canal, greater palatine nerve and Foramen rotundum.

Roof : The infraorbital nerve runs through the infraorbital canal in the midsection of the roof. This canal is reported to be dehiscent in 14% of cases. It is quite thin on both sides of the infraorbital canal.

Floor : Composed of the alveolar and palatine process of the maxilla. Level varies with that of the nasal floor. Generally at 9 years of age the sinus floor is at the same level as the nasal floor. Before age 9 the sinus
floor is at a higher level.

As growth continues, after age 9 the sinus floor is at lower level than the nasal floor. The most constant relations is with the three molar teeth. Closest is the first molar.

Accessory ostium : It is a non functional extra opening of the maxillary sinus in the lateral wall of the nose. Its number may vary from 1 to 5 and its incidence is 4% to 41 %. It is usually located in the posterior fontanelle but may be found at other sites such as the anterior fontanelle and the uncinate process. It may be a normal finding or result of infections of the maxillary sinus and breakdown of its membranous part.

Fig. 113:  Axial Section: Showing maxillary sinus. Postero-superior-medial pneumatization of maxillary sinus may be extensive and may mimic posterior ethmoid inus.  MS: Maxillary Sinus and E: Ethmoid Sinuses.

Fig. 114:  Coronal Section: Maxillary sinus showing an inter-sinus septa on (L) side.