Coronal Section at the level of the Nasion
- Scanogram, CT and Cadaver Coronal section and representative line diagram.
- Check list.
- Surgical Importance.
- Anatomy
- Frontal sinus.
- Frontal Sinus Drainage system.
- Frontal Recess.
Fig.9: Scanogram at Naison level.
Fig. 10: Cornoal Section at the level of Nasion in CT Scan.
Fig. 11: Representive Line Diagram.
Fig. 12: Coronal Section at the level of nasion in cadaver.
Fig. 13: Correlation of CT Scan with Cadaver section and representive line diagram.
Top
Check list
- Number, size and depth of frontat sinus.
- Number and position of inter-sinus septa.
- Dehiscence of inter-sinus septa.
- Septal deviation or spurs and maxillary crest.
- Look for frontal bulla and frontai cells. |
Top
Surgical Importance
Depth of the frontal sinus is most important dimension and should be studied in all sections and it gives clue about the space available for a safe entry into the frontal sinus floor. The septal tubercle or the widening of the nasal septum anteriorly is a normal finding and is due to thick cartilage and erectile tissue in the submucosal layer of the septum anteriorly. Septal tubercle can obstruct the view and passage of nasal endoscope but can easily compressed or pushed with suction cannula or septal elevator. |
Top
Frontal sinus
Development:
Starts: Late in intrauterine life (4-6th foetal months) or may start after the birth.
At birth: May be rudimentary.
Develops from: Pneumatic extension of the anterior ethmoid cells into the frontal bone.
Completion: Pneumatization and growth occurs from 1 -20 years. Growth is usually completed by ages 12 -14 years in women and 16-18 years in men.
Pneumatization: Starts in vertical segments, ie., squama and orbital parts of the frontal bone.
Agenesis: Seen in in 2-20% of cases, bilateral agenesis in 5% and unilateral agenesis in 4% of cases (Fig. 14)
Visibility : Radiologically visible by at least 6 years of age and is well pneumatized by age 12 years. By age20, it reaches full size.
Anatomy: The frontal sinus in adults averages 28 mm in height, 24 mm in width, and 20 mm in depth.
Adult size: Volume: 6-7 ml (Adult).
Chambers: Usually there will be two sinuses, one on each side, almost always asymmetrical, divided by thin bony inter sinus septa (Fig. 13 ), usually off the midline and rarely dehiscent.
Relations: Posteriorly, each sinus borders on the anterior cranial fossa. The lateral portion of the sinus floor overlies the orbital roof, whereas its medial portion is directly over the anterior ethmoid cells. The bones of the posterior wall and the orbital roof portion of the sinus floor are relatively thin. The anterior sinus wall especially the part overlying the root of the nose (the nasofrontal beak) is frequently the strongest.
Variations: The actual size and shape of the frontal sinus varies widely between individuals . Either the vertical or horizontal portions of the sinus may be unusually developed and invade the adjacent bones (Fig. 15 & Fig. 16). Posteriorly frontal sinus can pneumatize the whole roof of the orbit and involve anterior clinoid process. There may be more than two chambers (1.5% to 21 % population). The intersinus septa may be partially dehiscent, or there may be more than one inter- sinus septa or it may be so placed as to interfere with its drainage (Fig. 17 & Fig. 18).
Fig. 19: Coronal Section: Unilateral agenesis of Frontal sinus.
Fig. 20: Axial Section: Asymmetry of Frontal sinus with an osteoma of frontal sinus.
Fig. 21: Sagittal reconstruction of the frontal sinus showing an osteoma.
Fig. 22: Sagittal reconstruction of frotnal sinus showing antero-posterior duplication of the frontal sinus.
Fig. 23a: Axial section: Unilateral osteoma of the frontal sinus completely opacifying the sinus.
Top
Fig. 23b : Coronal section showing absent inter frontal septa with extensive vertical pneumatization of the frontal sinus.
Fig. 23c: Coronal Section: Frontal sinus with multiple inter-sinus septi.
Fig. 23d: Axial Section showing extensive posterior pneumatization of the frontal sinus.
Fig. 23e: Coronal section showing extenisve frontal pneumatization. In this the orbital process of the frontal bone is pneumatized upto anterior clinoid process. Below the frontal sinuses are posterior ethmoidal sinuses.
Frontal sinus drainage system
The connection between the frontal sinus and the nose is like an hour glass, with the sinus representing the upper portion, the isthmus the neck, and the frontal recess the lower portion. The opening of the frontal sinus into the isthmus can usually be found in the anteromedial portion of the sinus floor. This narrowest portion of the drainage system, the nasofrontal isthmus is bounded:
Anteriorly: by the nasofrontal process or beak,
Posteriorly: by the posterior sinus wall,
Anteroinferiorly: by the agger nasi cells. Just slightly anterolateral to the agger nasi is the lacrimal sac (Fig. 24).
Secretions from the agger nasi, supraorbital ethmoid cells, frontal cells and 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.
Top
Frontal Recess
Earlier frontal recess has been called by various confusing terms like the nasal part of the frontal sinus, the frontal infundibulum, and the nasofrontal duct.
Though, Killian, first used the term "frontal recess' in 1898, this became widely accepted only when Harris P. Mosher commented in 1912, "I was surprised to find that the nasofrontal duct was not a tube like structure at all."
The frontal recess may be thought of as an inverted funnel bounded:
Superiorly: by the skull base.
Laterally: lamina papyracea (superior and medial orbital walls). If the ethmoidalinfundibulum has a terminal recess, the uncinate process forms part of the lateral wall and also contributes to the floor of the frontal recess in its most anterior aspects.
Medially: the lateral surface of the most anterior portion of the middle turbinate (In this location middle turbinate fuses directly with skull base at the j unction of the fovea ethmoidalis and the cribriform plate).
Posteriorly : the bulla lamella of the ethmoid bulla. If bulla lamella is complete and ascends to the roof of the ethmoid, it separates lateral sinus from frontal recess (if there is one). If bulla lamella is incomplete, the frontal recess may freely communicate with the lateral sinus.
Anteriorly: the anterior wall of the agger nasi cell (Fig. 24).
Top |
