Surgical anatomy of the frontal sinus outflow pathway: a cadaveric study

Detailed anatomical knowledge of the variability in the drainage pathway in relation to the frontal sinus is a prerequisite for successful sinus surgery. We studied 32 mid-sagittal cadaveric heads and recorded the following parameters: drainage site of the sinus in relation to the uncinate process, attachment of the uncinate process, pneumatization of the agger nasi, and morphometric measurements for the localization of the frontal ostium during endoscopic surgery. Frontal sinus drainage was anterior to the uncinate process in 59.4% and posterior to it in 40.6%. In the majority of cases (59.4%), the uncinate process was found attached to the lamina papyracea. The mean diameter of the frontal ostium was 4.6 ± 1.6 mm. The angle formed by the plane of the frontal ostium to the floor of the nose was 26o ± 5.9o; the distance of the frontal beak to the anterior nasal spine was 46.50 ± 5.7 mm, while the distance of the frontal beak from the columella was 48.7 ± 4.8 mm. The corresponding angle between the frontal beak to the nasal floor (at the anterior nasal spine) was 70o ± 5o, while this decreased t o 56.6o ± 7.5o when the columella was the reference point. Pneumatization of the agger nasi was seen in 90% of specimens. The mean distance of the anterior ethmoidal artery was 9.0 ± 1.2 mm from the frontal beak, and 8.4 ± 1.8 mm from the posterior rim of the frontal ostium. These morphometric data should be of help in endoscopic surgery for accurate and safe negotiation of the frontal sinus drainage tract and for avoiding vascular injury.