The Horizon Sign and Frontal Bar: Two Topographic Landmarks to Confirm Endoscopic Frontal Sinusotomy.

Confirming a thorough dissection of the frontal sinus during endoscopic sinus surgery can be challenging, and some surgeons would benefit from reliable topographic landmark identification to ensure completion of this sinus dissection. We defined (1) the "horizon sign" as the curvilinear shadow of the posterior table cast superiorly upon the anterior table of the frontal sinus at the acute angle of their meeting point and (2) the "frontal bar" as a sagittal septation at the union of the anterior/posterior tables. A cadaveric study, followed by an intraoperative consecutive case series, was performed to evaluate these 2 landmarks as indicators of complete dissection. The horizon sign was extremely reliable, identified in 100% of cadaveric frontal sinuses and intraoperative frontal sinuses. The frontal bar was present in only 67% of frontal sinuses by computed tomography. In live patients, the sensitivity and specificity of the frontal bar were 62% and 95%, respectively.