A computer-assisted anatomical study of the nasofrontal region.

OBJECTIVES/HYPOTHESIS Objectives were as follows: 1) to define the variations of the uncinate process' superior attachment, 2) to study the diameter of the frontal sinus ostium, 3) to study the prevalence of the agger nasi cells, and 4) to evaluate the side-to-side variability of these structures. STUDY DESIGN A retrospective clinical study at a tertiary care center. METHODS One hundred forty-four consecutive computed tomography scans were studied with image-guided surgery software (InstaTrak, Visualization Technology, Inc., Wilmington, MA) that provides continuous coronal, sagittal, and axial sections. We reported the superior attachment sites of the uncinate process, the diameter of the frontal sinus ostium, and prevalence of the agger nasi cells. RESULTS The uncinate process' main superior attachment into the surrounding structures was found to have the following distribution: 52% to the lamina papyracea, 18.5% to the posteromedial wall of the agger nasi cell, 17.5% to the lamina papyracea and the junction of the middle turbinate with the cribriform plate, 7% to the junction of the middle turbinate with the cribriform plate, 3.6% to the ethmoid roof, and 1.4% to the middle turbinate. The frontal ostium anterior-posterior diameter (mean +/- SD) was 7.22 +/- 2.78 mm and its transverse diameter (mean +/- SD) was 8.92 +/- 2.95 mm. Agger nasi cells were found in 78% of the scans. CONCLUSIONS The frontal sinus opens into the middle meatus medial to the uncinate process in 88% of the patients and lateral to the uncinate process in 12% of the patients. The naturally wide dimensions of the frontal ostium help to explain why postoperative patency can be achieved merely by exposing the ostium without the need to enlarge it. The frontal ostium dimensions in one side may differ considerably from the contralateral side. An agger nasi cell or a terminal recess, or both, are found in most cases. Image-guided surgery software is a helpful new tool for anatomical studies and for preoperative evaluation.