The patient was taken to the operating room for immediate drainage with an image-guidance system (Fig. 3). Wide bilateral sphenoidotomy and left posterior ethmoidectomy were done to gain access to the lesion. In the sphenoid sinus, the left opticocarotid recess was filled by a soft tissue mass covered by erythematous mucosa. The mucosa was peeled off the mass, and the mucocele capsule was cut open under image guidance, resulting in mucoid drainage. The mucocele cavity showed no connection to the intracranial cavity.
The patient's postoperative course was uneventful. Within 1 week, the pain, diplopia, and afferent pupil defect had completely resolved. After a follow-up period of 8 months, endoscopic examination showed an open mucocele cavity with no evidence of recurrent disease. Imaging was not repeated.
Mucoceles usually involve the ethmoid or frontal sinuses and rarely the sphenoid sinus (11). Complete obstruction of the normal sinus outflow tract creates a confined cavity that cannot drain natural secretions from the mucosal lining. As a result, pressure rises within the sinus, expanding the sinus walls and exerting pressure on their surroundings.
Only 7 cases of isolated CM have been described (4-10) (Table 1). Infection (9) and trauma to the sphenoid sinus have been proposed as causative mechanisms, yet none of the reported patients had a history of sinus disease or trauma. Alternative mechanisms for mucocele development are epithelial rests or hyperplasia and bony overgrowth (2).
Because the anterior CP lies between the carotid artery and optic nerve, its expansion by mucocele may cause visual loss as the presenting symptom, as described in 5 of the 7 reports (4,6-8,10). Ophthalmoplegia and diplopia occur less commonly from pressure on ocular motor nerves in the superior orbital fissure area, as reported in 2 cases (9,12). Our patient presented with ophthalmoplegia and later developed an ipsilateral afferent pupil defect, indicating probable compression of the ocular motor nerves and the optic nerve.
CT and MRI are important for accurate diagnosis and localization of the lesion and for surgical planning. These imaging studies accurately defined the CM in our patient and in all but 1 reported case,(6) in which the lesion was mistakenly thought to be a tumor.
The differential diagnosis of anterior clinoid lesions includes meningioma, aneurysmal bone cyst (ABC), meningocele, and schwannoma. Meningioma is unlikely if the lesion is cystic and there is no hyperostosis or enhancement with contrasted CT. ABC commonly presents with bleeding and air-fluid levels. Meningocele would appear as a cystic lesion. Cystic schwannoma would not be centered at the CP and would typically enhance. The high signal intensity on T1 in our patient strongly suggested the high protein content of mucosal secretions and helped to rule in a mucocele.
Although 1 report (6) showed resolution of the CM with antibiotic treatment alone, the presence of visual loss or cranial neuropathy demands swift action to avoid permanent visual impairment (13) as occurred in 2 previous reports (4,10). Drainage was done through an open surgical approach in 4 reports (4,5,9,10); endoscopic drainage was described in 2 cases (7,8). Advances in endoscopic instrumentation, navigation systems, and intraoperative imaging have reduced the operative risk and made the endoscopic approach a feasible and safer alternative to open surgery for CM.
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