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Editor,—We describe a 68 year old man who suffered from progressive visual loss in his left eye to no light perception within 10 days and subtle involvement of ipsilateral cranial nerves V(1) and VI. Both computed tomography (CT) and magnetic resonance imaging (MRI) showed a left optic canal lesion with expansion to the superior lateral (anterior clinoid) and inferior walls of the optic canal. Left supraorbital craniotomy was performed by a neurosurgeon. A mucocoele containing turbid fluid in the left strut with compression to the optic nerve was found during the operation. After removal of the lesion, the patient’s best corrective visual acuity was improved to hand movements.
Though visual loss related to mucocoeles of the paranasal sinuses is not rare the frontal, ethmoid, and sphenoid sinuses are most often implicated. Only rarely has a pneumatised anterior clinoid been reported as a primary location for a mucocoele associated with visual loss.1 2 We report a case of anterior clinoid mucocoele producing optic neuropathy and other subtle cranial neuropathies. We emphasise the relation of the optic strut to the optic canal and the superior orbital fissure in producing a symptom complex distinct from optic neuritis and orbital apex syndrome.
A 68 year old healthy man noticed progressive loss of vision in the left eye 2 weeks before admission. He had had frequent attacks of headache in the temporoparietal region for 2 months, but denied orbital pain or double vision. He had a history of hypertension for about 10 years with good medical control. Non-insulin dependent diabetes mellitus was noted recently. On admission his blood pressure was 140/70 mm Hg. General neurological examination was normal. Visual acuity of the left eye was no light perception (NLP). There was an amaurotic pupil on the left. There was mild limitation of abduction of the left eye. Corneal sensation was mildly impaired in the left eye, and there was no epiphora. No proptosis was present. Ophthalmoscopy revealed normal optic disc, retina, and vessels in both eyes. CT and MRI showed a minimally enhancing lesion of the left anterior clinoid, which encroached upon the superior, lateral, and inferior walls of the optic canal (Fig 1). The optic nerve appeared to be compressed medially. The right anterior clinoid process was pneumatised, suggesting a possible mucocoele of left anterior clinoid process.
Under general anaesthesia, the left optic canal was exposed extradurally via a supraorbital craniotomy. Mucoid fluid leaked out as soon as the roof of the optic canal was opened. The postoperative CT scan showed complete removal of the lesion and decompression of the lateral wall of the canal (Fig 2). The patient was discharged 2 weeks after surgery when the visual acuity improved to light perception. In spite of successful decompression, optic atrophy developed eventually. Two years later, after surgery for cataract, the visual acuity in the left eye improved to hand movements.
Mucocoeles involving the optic canal are extremely rare. Optic canal mucocoele is an ophthalmological emergency, since, without effective management, complete visual loss may develop within a few days. Two reported cases of a mucocoele originating in the anterior clinoid process can be found from the literature.1 Both cases demonstrated bilateral pneumatisation of the anterior clinoid. The first patient developed severe visual loss with minimal recovery after surgery. The second patient, who declined surgery, had a recurrence of symptoms, resulting in optic atrophy. Another case report revealed significant visual improvement from 20/400 to 20/20 after surgery.2 Again, this patient had bilateral pneumatisation of the anterior clinoid, very similar to our presented case. The cause of the mucocoele formation is uncertain, since there is no known ostium to become obstructed. Cystic degeneration or secondary inflammation is the proposed mechanism.1 Pneumatisation of the sphenoid sinus can extend into the anterior clinoid. We believe that pre-existing anterior clinoid pneumatisation with secondary inflammation or degeneration rather than osteum obstruction is the cause of anterior clinoid mucocoele.
The optic strut is a segment of bone that joins the lesser wing of the sphenoid to the body of the sphenoid bone and forms the inferior and lateral walls of the optic canal, thus separating the canal from the superior orbital fissure.3 Thus, symptoms and signs from a lesion within the strut, such as mucocoele, may affect structures of the optic canal and the superior orbital fissure, simulating an orbital apex syndrome. Our case showed severe dysfunction of the left optic nerve and signs consistent with mild compression of the left cranial nerves V(1) and VI.
The differential diagnosis includes mucocoeles of the sphenoid sinus, retrobulbar neuritis, and space occupying tumours such as craniopharyngioma, Rathke cleft cyst, pituitary adenoma, epidermoid cyst and carcinoma, cholesteatoma, meningioma, lymphoid tumour, optic glioma, and arachnoid cyst.2-4 Reports of similar lesions are initially diagnosed as acute retrobulbar neuritis.2 3However the prevalence of retrobulbar neuritis in patients older than 60 is low. Tumour is considered unlikely in these cases because radiological studies reveal a lesion originating from within the optic canal and not from the brain parenchyma or meninges.
Surgical decompression is the treatment of choice for optic canal mucocoeles. For medial compression of the canal, a variety of otolaryngological external and internal approaches may be utilised. In this case, however, with mucocoele involving the lateral wall of the optic canal principally, the transcranial approach is preferred. A delay in surgery of more than 7–10 days after the onset of visual dysfunction is often associated with poor visual prognosis.2
We emphasise the importance of imaging in the evaluation of patients with atypical “optic neuritis.” Inappropriate age for onset of demyelinating disease is a general concern that should lead to additional examination. However, the importance of other subtle cranial neuropathies may help identify a lesion not only of the orbital apex but also of the optic structure which straddles the superior orbital fissure and the optic canal. Prompt diagnosis and surgical intervention may improve the visual outcome in these patients.