Risk Factors for Anterior Skull Base Injury in Endoscopic Sinus Surgery

Objectives This retrospective study aimed to investigate the relationships between the Keros classification, the Gera classification, the vertical height of the posterior ethmoid roof (ER), and anterior ethmoidal artery (AEA) types in Japanese patients. Methods We investigated the computed tomography (CT) slices of paranasal sinuses (120 sides) of 60 patients; measured the cribriform plate (CP) depth, lateral lamella CP angle (LLCPA), and vertical height of the lateral ER from the hard palate (LERHP) at the coronal plane of the posterior ethmoidal artery (PEA); and reviewed the AEA types, whether floating or non-floating. Results CP depth was positively correlated with LLCPA (r=0.63; p<0.01) and the height of LERHP (r=0.19; p<0.05). The height of the LERHP in females was significantly lower than that in males. With increased CP depth, floating AEAs became prevalent (p<0.001). Conclusion In females, low height of the posterior ethmoid sinus roof, where cerebrospinal fluid (CSF) leaks occurred while penetrating the basal lamella, often existed; the heights positively correlated with the Keros classification in Japanese patients. The Keros and Gera classifications, AEA type, and posterior ER height do not individually constitute a complete risk assessment but may correlate, preventing major complications, such as CSF leak and orbital hemorrhage.

An analysis of the anatomic variations of the paranasal sinuses and ethmoid roof using computed tomography

OBJECTIVE

To determine the Keros classification and asymmetrical distribution rates of the ethmoid roof and the frequency of anatomic variations of the paranasal sinuses.

MATERIALS AND METHODS

Paranasal sinus scans of 500 patients obtained using computed tomography were evaluated retrospectively. Measurements were performed using a coronal plan with right-left comparison and with distance measurement techniques. The depth of the lateral lamella was calculated by subtracting the depth of the cribriform plate from the depth of the medial ethmoid roof. The results were classified according to their Keros classification. Any asymmetries in the ethmoid roof depth and fovea ethmoidalis configuration were examined. The anatomic variations frequently encountered in paranasal sinuses (pneumatized middle concha, paradoxical middle concha, agger nasi cells, Haller cells, Onodi cells, etc.) were defined.

RESULTS

The mean height of the lateral lamella cribriform plate (LLCP) was 4.92±1.70 mm. The cases were classified as 13.4% Keros Type I, 76.1% Keros Type II, and 10.5% Keros Type III. There was asymmetry in the LLCP depths of 80% of the cases, and a configuration asymmetry in the fovea in 35% of the cases. In 32% of the cases with fovea configuration asymmetry, there was also asymmetry in the height of the right and left LLCP. The most frequent variations were nasal septum deviation (81.8%), agger nasi cells (63.8%), intralamellar air cells (45%), and concha bullosa (30%).

CONCLUSION

Using the Keros classification for LLCP height, higher rates of Keros Type I were found in other studies than in our study. The most frequent classification was Keros Type II. The paranasal sinus variations in each patient should be carefully evaluated. The data obtained from these evaluations can prevent probable complications by informing rhinologists performing endoscopic sinus surgery about preoperative and intraoperative processes.