At the level of agger nasi

Sub-contents

- Scanogram, CT & Cadaver Coronal Section and representative line diagram.
- Checklist.
- Surgical importance.
Anatomy:
     - Frontal recess variaitons.
     - Frontal cells.
     - Agger Nasi cells.
     - Nasolacrimal drainage system.
     - Infra-orbital ethmoidal cell.

Fig. 25:  Scanogram at Agger nasi level.

Fig. 26:  Cornoal Section at the level of Agger nasi in CT Scan.

Fig. 27:  Representive Line Diagram.

Fig. 28:  Coronal Section at the level of Agger nasi in cadaver.

Fig. 29:  Correlation of CT Scan with Cadaver section and representive line diagram.

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Variations of Frontal recess

The size and shape of the frontal recess are influenced by the degree of pneumatization of the bulla ethmoidalis, agger nasi or other anterior ethmoid cells which may compromise outflow from the frontal sinus. If there is marked pneumatization of the agger nasi (Fig. 30 & Fig. 31) and additional frontal ethmoidal cells, the frontal recess may be narrowed to a small tubular lumen (Nasofrontal duct?). The middle turbinate can also become pneumatized from the frontal recess. The anatomic situation can be further complicated in that the most anterior ethmoid cells or frontal cells may develop from the frontal recess.

Nasofrontal duct:

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Frontal Cells

Four types of frontal cells have been recognized and classified. Each type is derived from the anterior ethmoid sinuses and pneumatizes above the agger nasi region.

Type I (Fig. 32):  A single cell pneumatizing above the agger nasi cell but below the floor ofthe frontal sinus.
Type II (Fig. 33): A tier of two or more cells above the agger nasi cells.
Type III (Fig. 34): A massive single cell above the agger nasi cell that extends into the frontal sinus.
Type IV (Fig. 35): A single cell isolated within the frontal sinus that has no discernible connection to the frontal recess.

Secretions from the agger nasi and supraorbital ethmoid cells, and the frontal sinus empty into the frontal recess. Depending on the position of the uncinate process, these secretions may then drain directly into the middle meatus or into the nasal cavity via small cleft between the superior aspect of the uncinate process and the middle turbinate or into the ethmoid infundibulum.

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The agger nasi cells

The Agger nasi cells or infundibular cells, are the most consistent anterior ethmoid cells. They pneumatize the lacrimal bone that are juxtaposed against the hard nasal bones and as a rule, they are always anterior to the attachment of the middle turbinate and have an important role in the pathogenesis of frontal recess obstruction.

Endoscopically agger nasi cells appear as a mound or eminence (meaning 'mound in the nose')on the lateral wall of the nose anterior to the origin of the middle turbinate.

Fig. 43: Endoscopic Picture of the Agger Nasi.

The prevalence of the agger nasi cells has been reported to range from 40% to 60% in early anatomic studies to nearly 100% in recent radiographic examinations. It is believed to originate from the infundibulum and from the first embryologic frontal pit. The boundaries are:

Anteriorly: the frontal process of the maxilla

Posteriorly: the infundibulum

Superiorly: the frontal sinus and its recess,

Inferomedially: the uncinate process,

Laterally: the nasal and lacrimal bones and therefore the lacrimal sac lies just anterolateral to these cells.

On sagittal dissection, the agger nasi cell may be seen anterosuperior to the middle turbinate and anterior to the uncinate process.

Variations : The location and extent of pneumatization of the agger nasi cell vary widely. When there is extensive pneumatization, an enlarged agger nasi air cell may fill the frontal recess causing obstruction and may displace attachment of the middle turbinate medially and superiorly.

Fig. 30: Large single Agger nasi cell.

Fig. 36: Bilateral Agger nasi cells with pathology on ( L) side (Mucosal hypertrophy).

Fig. 37: Unilateral Agger nasi cell pathology with Frontal sinus disease (R).

Fig. 38:  Bilateral Agger nasi cells pathology with (R) frontal disease.

Fig. 39:  Agger nasi pneumatizing uncinate process.

Fig. 40. Multiple Agger nasi cells. Note Frontal bulla on (R) side.

Fig. 41:  Agger Nasi pushing the middle turbinate medially and superiorly.

Fig. 42: Agger nasi with lacrimal bone dehiscence and Mucocoele.

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Lacrimal drainage system

The lacrimal system is divided into secretory and excretory components. The excretory portion of the lacrimal system consists of the canaliculi (upper and lower), common canaliculus, lacrimal sac, and nasolacrimal duct (Fig. 44  & Fig. 45).

Fig. 44 : Lacrimal drainage system.

Tears pool initially at the lacus lacrimalis of medial canthus and are then collected by superior and inferior puncta of the upper and lower lid, respectively. Each punctum leads into the vertical portion of the superior and inferior canaliculus, which, after traveling vertically approximately 2mm, makes an acute angle to lie parallel to the line of the lid. The superior and inferior canaliculi join to form the common canaliculus and enter the lacrimal sac approximately 8 to 10 mm from the puncta.

The lacrimal sac is contained within the lacrimal fossa, a bony groove formed anteriorly by the stout frontal process of the maxilla and posteriorly by the delicate lacrimal bone. The sac courses inferiorly approximately 10 to 15 mm and narrows to form the nasolacrimal duct, which enters bony canal composed of the maxilla anteriorly, lacrimal bone posteriorly and partly inferior concha medially. This interosseus portion of the LDS measures approximately 10 to 12 mm and terminates in a poorly developed fold of nasal mucosa (Valve of Hasner) in the inferior meatus. The direction of the osseous nasolacrimal canal is downwards, backwards and lateral, The lower half of the lacrimal fossa is related medially to the anterior part of the nasal middle meatus; the upper half to the anterior ethmoidal sinuses.

As such agger nasi cell pneumatizes the lacrimal bone only a thin plate of bone separates the agger nasi cell from the lacrimal foisa and agger nasi cell lies immediate posterior, medial, and superior to the nasolacrimal duct (Fig. 44). The nasolacrimal duct lies only 2mm (range 1-8mm) anterior to the root of the uncinate rocess Average distance from the natural maxillary ostium to the duct is 4mm (range 0.5 to 18 mm).

Variation in the basic anatomic pattern have been reported. The wide variation seen in human subjects regarding the width of the nasal dorsum, width of the piriform aperture, and projection of the midface, may influence the course of the nasolacrimal canal. Apart from agger nasi cells, other anterior ethmoid air cells have also been found to arise from the ethmoid infundibulum and frequently pneumatizes the lacrimal fossa.

In 100 skulls Whitall (1911), observed that in 14 anterior ethmoidal sinuses, were related only to ti'i3 fossa's posterior wall; in 32 they reached the suture between the lacrimal bone and maxilla; in 54 one irregular sinus extended to the anterior lacrimal crest. The osseous walls separating the mucous membrane iif the ethmoidal cells and the lacrimal sac frequently have been found to be dehiscent even under normal conditions and the lacrimal bone itself may be completely absent in 0.9% of specimens.

The bone between the maxillary sinus and the osseous nasolacrimal canal can also be thin, varying in thickness from 3 mm down to a paper-thin bone. At times, this bone as well as the lacrimal bone, can be totally dehiscent (Fig. 46, Fig. 47, Fig. 48 & Fig. 49).

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Infraorbital ethmoidal cell

Also called the Haller's cell, an infraorbital cell is any ethmoid cell that extends inferior to the ethmoid bullae and lateral to the maxillary sinus roof and that interposes itself between the lamina papyracea and the uncinate process. It is usually located in the anterior ethmoid but may extend all the way from anterior to the posterior. It is seen distinct from the bulla and the maxillary floor. Incidence is 10% of the population. Unilateral in 5.4% and Bilateral in 4.5%   (Fig. 50, Fig. 51, & Fig. 52).

Fig. 50: Haller cell (Arrow), CB: Concha Bullosa, MS: Maxillary Sinus.

Fig. 51: Multuiple Haller's cells (White arrows) narrowing the ethmoid infundibulum with disease in the maxillary sinus. Uncinate Process (Gray arrow), MS: Maxillary sinus, CB: Concha bullosa.

Fig. 52: Large and Flat Haller's cell(Arrow) occupying the whole roof of Maxillary sinus.

Fig. 53: Haller cell obstructing the Ethmoid infundibulum with disease in the maxillary sinus (Black arrow). Uncinectomy has been done (White arrow).