Background: Arachnoid cysts of the paranasal sinus are rare. They have not been described yet in the sphenoid sinus.
Patient and method: Microscopic-endoscopic endonasal surgery of the sphenoid sinus was performed on a 34-year-old female with a history of chronic headaches and a suspected mucocele of the sphenoid sinus in computed tomography (CT) and magnetic resonance imaging (MRI) studies. An extended arachnoid cyst was found in the enlarged sphenoid sinus, which was obliterated with collagen, fibrin glue, and abdominal fat.
Results: There were no complications after the operation, and 12 months later the patient is still free of symptoms.
Conclusion: Arachnoidal cysts present in CT and MRI as fluid dense lesions that can imitate a mucocele.