Incidence, Potential Mechanisms, and Clinical Significance of Cavernous Sinus Air Sign

Background/Objectives: The cavernous sinus air sign, historically linked to trauma or venous sinus thrombosis, has recently been reported in association with retrograde venous air embolism, often without clinical significance. Despite this, its exact prevalence, etiology, and clinical relevance remain unclear. This study aims to systematically evaluate the incidence of the cavernous sinus air sign in patients undergoing CT angiography (CTA) and to assess its potential clinical implications. Methods: We retrospectively analyzed data from patients who underwent CTA between January 2021 and December 2021. The cavernous sinus air sign was defined radiologically as air-density foci within the cavernous sinus, with Hounsfield units lower than those of orbital fat. Key variables included clinical indications for CTA, evidence of venous reflux of contrast media, the laterality of contrast injection, and the presence of brachiocephalic vein stenosis. Comparative analyses were performed to identify factors associated with the occurrence of the cavernous sinus air sign. Results: Among the 2,821 patients evaluated, the cavernous sinus air sign was identified in 35 cases (1.2%). Notably, none of these patients had a history of trauma or venous sinus thrombosis. Follow-up CT imaging was available for 27 of the 35 cases (77.1%), and in all instances, the cavernous sinus air sign resolved spontaneously. A statistically significant association was found between the cavernous sinus air sign and left-sided peripheral intravenous contrast injection, observed in 8.6% of affected patients compared to 1.5% in those without the sign (p = 0.001). Venous reflux into the internal jugular vein was also more frequent in patients with the air sign (34.3% vs. 14.1%, p = 0.001). These findings suggest a mechanical component, likely related to retrograde air embolism, influenced by anatomical and procedural factors. Conclusions: The isolated presence of the cavernous sinus air sign, in the absence of relevant clinical conditions, is most likely a benign, incidental finding associated with retrograde air embolism.