Anatomical Changes of the Ethmoid Cavity After Endoscopic Sinus Surgery

OBJECTIVE: 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. STUDY DESIGN: Retrospective review performed at an academic medical center. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.