Anatomy of the ethmoid: CT, endoscopic, and macroscopic.

Many operations have been devised and are performed for the surgical treatment of severe chronic inflammatory disease and polYPosis of the ethmoid . Although internal transnasal ethmoidectomy was discredited for many years because of possibly severe complications, it is now regaining in popularity and is preferred over external transmaxillary and transfacial procedures [1-3) . This is the result of recent more conservative operative techniques based on endoscopic control and the use of angle optics allowing enhanced visualization of the surgical field . However, transnasal ethmoidectomy is still difficult and dangerous. The ethmoidal labyrinth has great anatomic variability and few landmarks. Furthermore, the upper paranasal sinuses are close to important organs and structures. Penetration beyond one of the walls into the eye laterally or the brain superiorly may entail very serious complications (4) . A detailed radiologic preoperative evaluation of the topographic relations is therefore essential for planning and executing this procedure. High-resolution thin-section computed tomography (CT), capable of accurately depicting the thin bony septa of the ethmoid bone and the superior paranasal sinuses, even in the presence of severe inflammatory softtissue changes, may provide a method for precise preoperative surgical mapping. We illustrate the normal CT anatomy of the ethmoid region and correlate it with the endoscopic and macroscopic anatomy to define landmarks that can be recognized on CT and during endoscopically controlled transnasal ethmoidectomy.