Objectives/hypothesis: The depth of the frontal sinus was measured using axial computed tomography (CT) images to examine the safety of frontal sinus trephination at selected distances from the midline.
Study design: Review of 200 sinus CT scans.
Methods: Two hundred sinus CT scans (400 frontal sinuses) were reviewed to measure the frontal sinus depth at 5 mm, 10 mm, and 15 mm from midline.
Results: Males had a significantly deeper frontal sinus than females at all measurements points (P < .001). The measurements revealed a considerable number of small but nonhypoplastic frontal sinuses, which were shallower than the length of standard frontal trephine instruments (7 mm) and would risk penetration of the posterior table of the sinus. Of all frontal sinuses studied, 9.54% were <7 mm deep at 5 mm from the midline, 10.12% at 10 mm, and 8.96% at 15 mm from the midline. Overall, 15.3% of all frontal sinuses studied had at least one point where the measured depth was <7 mm.
Conclusions: Although the majority of patients have frontal sinuses deep enough to accommodate standard trephine instruments, surgeons should recognize that up to 15% of nonhypoplastic frontal sinuses may not be sufficiently deep at a given point to allow safe trephination without risking unintentional transgression of the posterior table. This study suggests that trephination routinely carried out at a given predetermined distance from the midline may be an unsafe practice. Careful evaluation of the imaging is essential in every case to avoid inadvertent injury and to help select the safest distance from the midline for frontal sinus trephination.