A 17-year-old girl presented with headache, and right third and left sixth nerve palsies. MRI was performed. Coronal T1-W image after gadolinium administration (Fig. 1) demonstrated enlargement and pathological enhancement of the left cavernous sinus (arrow) with narrowing of the left internal carotid artery (arrowhead). Axial T2-W image (Fig. 2) showed opacification with high signal intensity in the ethmoid air cells. There was sphenoid sinus signal abnormality within an enlarged left cavernous sinus (arrow) involving a narrowed carotid artery (arrowhead).

Fig. 1
figure 1

Coronal T1-W image after gadolinium administration

Fig. 2
figure 2

Axial T2-W image

Cavernous sinus thrombosis/thrombophlebitis (CST) is a rare, albeit potentially life-threatening, complication of paranasal sinusitis [1]. CST is most often associated with sphenoid or ethmoid disease and is spread through afferent and efferent venous extension via a network of valveless veins and also direct extension [2]. Signs and symptoms include fever, headache, ptosis, proptosis, chemosis, external ophthalmoplegia and decreased corneal reflex [1]. A high index of suspicion and emergent imaging are crucial to making an early and accurate diagnosis.