An anatomic classification of the ethmoidal bulla.

OBJECTIVE The ethmoid bone is arguably the most complex and varied osseous structure in the human body. The partitions within form a unique labyrinth of lamellae and spaces from specimen to specimen or, as in this study, from patient to patient. The surgical anatomy of the ethmoid bone, and the ethmoidal bulla in particular, is ill-defined and heretofore largely unclassified. In an attempt to better understand the ethmoid labyrinth, a prospective anatomic study of 107 patients undergoing primary intranasal endoscopic ethmoidectomy was undertaken. STUDY DESIGN Two hundred fourteen ethmoidal bullae were dissected intraoperatively with video-documentation obtained in over 90% of cases. Based on these dissections, the compartments or cells formed by the partitioning within the ethmoidal bulla and the respective communication with adjacent spaces were the parameters used to develop the classification system. SETTING Private midwestern rhinologic referral practice. RESULTS Three main categories of ethmoidal development were identified: simple, compound, and complex. Forty-seven percent of bullae were of the simple type, 26% were compound, and 27% complex. Sixty-eight percent of ethmoidal bullae had a single opening into the hiatus semilunaris superior; 6 (2.8%) ethmoidal bullae had a single anterior opening to the ethmoidal infundibulum. The remaining 28.7% had multiple cells with multiple openings, at least 1 of which opened into the hiatus semilunaris superior 98.4% of the time. There was a cell in the complex bulla opening anteriorly to the ethmoidal infundibulum in 46.5%. In 58% of cases, there was symmetry from side to side. CONCLUSION A novel anatomic classification for the ethmoidal bulla is presented, with examples of the 3 types of sinus development encountered. We believe that understanding ethmoid sinus anatomy and potential drainage pathways is a core principle to functional sinus surgery.