Bony Dehiscence in the Lateral Wall of the Sphenoid Sinus: Prevalence and Its Implication

Objective: According to the literature, bony dehiscence at the lateral wall of the sphenoid sinus is reported to be rare. However, authors have experienced frequent bony dehiscence of sphenoid sinus in patients with sphenoid fungus ball. Therefore, this study evaluated the prevalence of bony dehiscence of sphenoid sinus according to pathology.

Methods: This is a single-center study with retrospective analysis during January 2017 to January 2019. First, patients who had been treated with sphenoid fungus ball (SFB) were recruited. This was followed by recruitment of age- and sex-matched patients with bilateral chronic rhinosinusitis (CRS) or with pituitary adenoma (PA). Presence and width of the bony defect were measured in the coronal section of paranasal sinus CT scan with 2 mm thickness in the bone setting. For sphenoid fungus ball, the ipsilateral side was selected for analysis, and for others, side of analysis was selected randomly.

Results: In total, 65 patients were analyzed (27 SFB, 15 PA, 23 CRS). All bony defects were located medial to foramen rotundum and superior orbital fissure, just anterior to opticocarotid recess. In SFB, bony defects were present in 74.1% (20/27) and were significantly more frequent compared with PA (20%) and CRS (26.1%; p < 0.001). The width was highest in SFB (1.24 ± 6.96 mm) followed by CRS (0.79 ± 0.18 mm) and PA (0.72 ± 0.32 mm). However, the difference was not significant (p = 0.304). Bony ostitis was most frequently observed in SFB (88.8%) followed by CRS (56.5%) and PA (0%). Logistic regression revealed that the presence of bony defect was more dependent on the presence of ostitis rather than on sinus pathology. During the study period, three patients with SFB presented with invasive fungal sinusitis. In two patients, lateral wall defect was the route on invasion to the skull base.

Conclusion: Sphenoid sinus lateral wall defect is more frequently observed when the bony ostitis is present. In SFB in which bony ostitis is common, this bony defect could be a route of skull base invasion.