Objective: To study the pattern of the nasofrontal drainage in relation to the neighboring anatomical structures in adult Thai cadavers.
Material and Method: The anterior aspect of the frontal bone of the embalmed half-head was drilled to identify the presence of the frontal sinus i.e. 40 from only one side of each cadaver were chosen. A silicone base and catalyst were combined then injected into the frontal sinus, which flowed into the nasal cavity through its natural ostium, thereby creating a cast of the nasofrontal connection(s). After allowing five minutes for the silicone to set, the total vertical lamella of the middle turbinate was removed, so the cast could be measured, the connections meticulously dissected and the surrounding structures observed.
Results: The investigation revealed five patterns of nasofrontal drainage. The most (60%) common pathway was directly through the frontal recess, while the other pathways 12.5, 10, 10 and 7.5 percent were drained directly into the ethmoid infundibulum, through the agger nasi cell and then into the ethmoid infundibulum, into both the agger nasi cell, the ethmoid infundibulum and the suprabullar recess, respectively. The average sizes of the anteroposterior and mediolateral diameters of the frontal sinus ostium were 6.5 and 5.5 mm, respectively. The agger nasi cell was present in every cadaver with a frontal sinus and was always superior to the ventral attachment of the middle turbinate.
Conclusion: The agger nasi cell is the key structure vis-a-vis planning and performing frontal sinus surgery. In preparation for endoscopic intranasal frontal sinus surgery, it is practical to extend the infundibulotomy superiorly into the agger nasi cell, then remove its medial, posterior and superior wall.

Keywords: Frontal sinus drainage, Nasofrontal drainage pathway, Frontal sinus surgery, Endoscopic sinus surgery, Agger
nasi cell