Anatomical Changes of the Ethmoid Cavity After Endoscopic Sinus Surgery

Abstract

Alteration of the bony architecture of the sinus cavities has been observed in chronic sinusitis. Plasticity of the ethmoid sinus framework after endoscopic surgery, however, is a newly described entity. The objective of this study was to determine the incidence and extent of changes in ethmoid size after ethmoidectomy. Retrospective review performed at an academic medical center. Computed tomography scans performed from 2006 through 2007 at the Massachusetts Eye and Ear Infirmary (n = 5,131) were reviewed to identify 100 consecutive patients who underwent sinus surgery and met inclusion criteria. Seven dimensions were measured for each pre- and postoperative scan (n = 200) using Voxar 3D software. Computed tomography scans performed before and 2 to 37 months after ethmoidectomy demonstrated a decrease of 1.1 +/- 1.6 mm in mean ethmoid cavity width at the level of the cribriform plate and posterior globe after surgery (P < .0001). Twenty-five patients (25%) had >1 mm decrease in mean ethmoid width, and six patients (6%) had a decrease of >2 mm (mean 3.1 +/- 0.9 mm). These findings seemed to be the result of postoperative bowing of the medial ethmoid walls with a corresponding increase in orbital volume. These volumetric changes resulted in a postoperative subclinical retrodisplacement (enophthalmos) of the globes (mean 0.2 +/- 0.8 mm, P = .008). The extent of surgery, including performance of frontal recess dissection (P = .007) and total ethmoidectomy (P = .021) were found to be independent predictors of the observed changes in sinus dimensions. Postsurgical plasticity of the ethmoid cavity is a new concept supported by observed changes in sinus dimensions after ethmoidectomy. These changes may reflect a loss of internal structural support and forces of contracture during the postoperative healing period.