Department of Otolaryngology Head and Neck Surgery, Singapore General Hospital, Singapore.
Address correspondence to Boaz Forer, MD, Department of Otolaryngology, Head and Neck Surgery, (Block 6, Level 6), Singapore General Hospital, Outram Road, Singapore; E-mail: email@example.com
A 50-year-old Chinese man presented with rapidly progressive unilateral ophthalmoplegia and then an ipsilateral afferent pupil defect. CT and MRI revealed a mass centered in the anterior clinoid process causing bone destruction and showing high T1 and T2 signal intensity indicative of mucosal protein secretion. These imaging features suggested a mucocele, which may have resulted from sequestration of a clinoidal extension of the sphenoid sinus. The sphenoid sinus was opened via an image-guided endoscopic approach, and the lesion incised. There were no complications. The ophthalmoplegia and afferent pupil defect had completely resolved within 1 week of surgery. This is the eighth reported case of anterior clinoidal mucocele, a rare cause of ophthalmoplegia or optic neuropathy. 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 this condition.
The anterior clinoid process (CP) is a bony structure on the superolateral aspect of the sphenoid sinus that lies between the internal carotid artery and the optic nerve. In some patients, the CP is pneumatized during skull base development, creating a pocket of air with a narrow opening between the optic nerve and carotid artery that communicates with the sphenoid sinus (1). Closure of this opening might create a clinoid mucocele (CM) (2), which is exceedingly rare as a localized lesion without involvement of the sphenoid sinus. Such a mucocele could gradually expand to exert pressure on the optic nerve and orbital apex (3). CT and MRI help to establish the diagnosis of CM. The treatment of CM is surgical with very few reports (4-10). We report a case of CM and discuss its diagnosis and treatment.
A 50-year-old Chinese man with no medical history presented to the emergency department with a 2-day history of left eye redness and pain. He denied headache, vomiting, fever, or nasal symptoms. Neuro-ophthalmological examination revealed mild left eye ptosis, conjunctival injection, and reduced ductions in all directions. Intraocular pressure was normal. The ductions of the right eye were normal. Pupils were equal in size and constricted normally to a light stimulus. There was no afferent pupil defect. Visual acuity and ophthalmoscopy were normal.
The next day, the patient complained of pain exacerbation. Pupil examination revealed diminished light reflex on the left eye with a relative afferent pupil defect. Visual acuity remained normal.
CT showed a soft tissue lesion causing bone destruction, which was centered at the CP with mild protrusion into the left sphenoid sinus (Fig. 1). MRI revealed a smooth dumbbell-shaped mass located between the optic nerve and carotid artery with increased signal intensity on T1 without enhancement and with increased signal intensity on T2 (Fig. 2). These imaging features were suggestive of a cystic lesion with mucoid (protein rich) content, probably a clinoidal mucocele.
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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