Ethmoid skull-base height: a clinically relevant method of evaluation.

BACKGROUND

The Keros classification scheme has been used to describe the ethmoid skull-base configuration; however, this scheme only partially addresses key anatomic issues in ethmoid skull-base injury avoidance during surgery.

METHODS

Coronal computed tomography (CT) scans were reviewed for 200 patients undergoing sinus evaluation at a tertiary care institution. Keros classification, maxillary sinus:ethmoid height ratio, and the skull-base height:orbital height ratio were recorded for each patient. The Pearson correlation coefficient was used to determine if a relationship existed between the 3 sets of measurements.

RESULTS

In the Keros classification scheme, 42% of patients were in class I, 50% class II, and 8% class III. In maxillary sinus to ethmoid height ratio, 58% were 1:1, 37% were 2:1, and 5% were >2:1. In the skull-base height to total orbital height ratio, 65% were in class I, 18% class II, and 17% in class III. There was no correlation between the classification schemes.

CONCLUSION

The importance of the Keros classification lies primarily in the avoidance of iatrogenic injury to the cribriform region and medial ethmoid roof. To avoid penetration of the ethmoidal roof, the ethmoid skull-base height must be separately examined in relation to the orbit and total vertical dimension of the sinuses.