Objective: To characterize the anatomy of the sinus lateralis and enable a more accurate and safe approach to endoscopic ethmoidectomy. Study Design: An anatomic study of 33 cadaver heads providing a prospective evaluation of 50 ethmoid sinuses. The sinus lateralis, in particular, was thoroughly examined and typical variations were classified into four categories. A technique using the sinus lateralis as a critical landmark is described which allows calculated removal of anterior ethmoid cells in a posterior-to- anterior direction, avoiding inadvertent entry into the posterior ethmoid. Prospective evaluation of this technique in 12 pediatric patients found it to be safe and particularly useful for neophyte endoscopic surgeons. Methods: Endoscopic examination of 50 cadaver sinuses using 0-, 30-, and 70-degree, 4- mm telescopes to dissect the anterior ethmoid. The characteristics of each sinus lateralis were documented. To confirm the endoscopic findings, we grossly examined each specimen. Results: Four different categories of sinus lateralis formation were identified: type I (n = 22), posterosuperior extension to skull base; type II (n =15), posterior extension to sphenoid face; type III (n = 8), abrupt termination posterior to ethmoid bulla; and type IV (n = 5), extension into posterior ethmoid through dehiscent basal lamella. Conclusions: The sinus lateralis is a consistent feature of the anterior ethmoid. Type I and II patterns are most conducive to the aforementioned technique. Type III is the most difficult to identify endoscopically, whereas type IV is most apt to encourage an unplanned posterior ethmoidectomy. Regardless of the chosen ethmoidectomy technique, careful assessment of the sinus lateralis should enable more accurate and safe removal of ethmoid disease with reduced complications.
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