A channel for venous blood placed either side of the sphenoid bone at the base of the SKULL behind the eye sockets. Blood drains into it from the eye, the nose, the brain and part of the cheek, and leaves via the internal jugular and facial veins. Sometimes the sinus becomes blocked by a blood clot (thrombus), usually a complication of a nearby bacterial infection. A potentially serious condition, it should be treated with thrombolysis and antibiotics.
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