[Drainage pathways of the frontal sinus on oblique multi-planar reconstruction CT scans].

Oblique reconstruction CT images of frontal sinus drainage pathways were created with ONIS which is free DICOM viewer software. By placing the slice line of the cross sectional image on the drainage pathway of the frontal sinus in the sagittal view, the key oblique CT image could be generated in 96.9% of 65 normal paranasal sinuses that showed the frontal sinus and its drainage pathway simultaneously in one slice. The route of the drainage pathway was divided by the line of the uncinate process, and three variations were defined as follows: (1) inside, (2) outside to inside, and (3) outside. Additionally, three variations of the upper attachment site of the uncinate process were defined as follows: (1) outside: orbital wall, (2) upside: skull base or intersinus septum of the frontal sinus, and (3) inside: middle turbinate. The uncinate process was attached to the "outside" in 66.7%, and all of them had the "inside" pathway of drainage. The rest of them in whom the uncinate process was attached to the "upside" or "inside" had a drainage pathway of "outside to inside" or "outside." The anatomical relations between the frontal sinus and the anterior ethmoid cells such as agger nasi cell, frontal ethmoidal cell and intersinus septal cell were reasonably explained with these variations in the drainage pathway. The key oblique CT image showing the frontal sinus drainage pathway is the imaginary plane of the surgical pathway of instruments while they are inserted into the frontal sinus. Therefore, using the oblique CT image together with the sagittal CT image, we can get valuable information about the three dimensional anatomy of the frontal sinus before and during frontal sinusotomy.