Isolated sphenoid sinus diseases are generally asymptomatic and relatively uncommon with the potential for serious complications. Patients with this condition should be monitored closely and treated aggressively and either diagnostic or therapeutic intent is often indicated. In the management of a complex, life-threatening condition that involves many different fields of expertise, the otolaryngologist plays a key role in orchestrating different specialists and gaining direct access to the affected area, thus taking the first and essential step towards diagnosis and therapy. Because of the superiority of computed tomography in defining the bony margins and the superior soft tissue resolution of magnetic resonance imaging, these two techniques should be used in a complementary manner in the evaluation of isolated sphenoid sinus disease in addition to mapping the lesion better and identifying intracranial and intraorbital extent. We report an unusual case of isolated rhinosinusitis of the sphenoid sinus involving the cavernous sinus, pterygoid fossae and masticatory space in an immunocompetent patient.