First olfactory fiber as an anatomical landmark for frontal sinus surgery.

OBJECTIVES/HYPOTHESIS Access to the frontal sinuses is technically challenging owing to their anterosuperior location, diverse anatomy, close proximity to critical structures and the need to work in a relatively narrow space with angled-lens endoscopes and instruments. This study attempts to study the relationship of the first olfactory fiber with the frontal sinus posterior wall, assessing its fidelity as a surgical landmark during frontal sinus surgery. STUDY DESIGN Anatomic study. METHODS Fifteen cadaveric specimens were studied. Measurements were obtained bilaterally using the data from individual CT scans. Median A-P was defined as the anteroposterior (A-P) diameter measured just lateral to the intersinus septum, paramedian A-P was measured 5 mm lateral to the septum, and maximum A-P was defined as the maximum anteroposterior diameter on axial images. A surgical navigation device was used to calculate the distance between the first olfactory fiber and the posterior table of the frontal sinus. RESULTS The mean distance between the first olfactory fiber and the posterior wall of the frontal sinus was (4.03 ± 2.7) mm on the right side and (4.2 ± 2.9) mm on the left. This distance strongly correlated with the maximum A-P diameter of the sinus. CONCLUSIONS In a cadaveric model, the first olfactory fiber was found to be an average of 4.0 mm posterior to the frontal sinus. The significant variability of this distance should be considered when using the first olfactory fiber to establish the posterior boundary of a frontal sinusotomy. Drilling no further posterior than 7 mm rostral to the first olfactory fiber would be safe in 91% of patients. LEVEL OF EVIDENCE NA Laryngoscope, 126:1039-1045, 2016.