Endonasal Management of Optic Canal Stenosis Due to Fibrous Dysplasia

Background: Fibrous dysplasia (FD) is a bone growth abnormality where normal bone is replaced by fibrous, often expansile, bone tissue. Skull base involvement with FD can impinge neurovascular structures leading to neuropathy and functional loss.

Clinical Case: A 9-year-old previously healthy boy was referred for further management of a new diagnosis of severe left visual loss associated with mild left proptosis. Examination showed normal right-eye vision but minimal light perception in the left eye associated with an afferent pupillary defect (AFD) and optic nerve atrophy. The child had not noted a change in vision and was unsure how long the loss was present. Three years prior, he had documented normal vision in both eyes. Computed tomography (CT) scan and magnetic resonance imaging (MRI) showed findings consistent with extensive FD of the skull base with severe narrowing of the left orbital apex and optic canal. Mild to moderate narrowing of the intracanalicular right optic canal was also noted. The child was admitted to the hospital for IV Decadron and a left optic canal decompression. The surgery was accomplished by a left pterional craniotomy and microscopic dissection. Postoperatively, the child did not recover any vision in the left eye. After recovery, he was discharged home with close follow-up to monitor vision in the right eye.

Five months later, the child presented to the emergency department with right eye blurry vision, pressure, and swelling. Examination showed mild right optic nerve edema with normal visual acuity. CT scan and MRI were stable compared with previous studies with moderate right intracanalicular segment optic canal stenosis. Symptoms resolved overnight with IV Decadron, and he was discharged home on a Decadron taper. Over the next 2 months the child had increasingly frequent episodes (eventually 1-2 per day) of transient (1-2 minutes per episode) blurry vision on the right.

The decision was made to proceed with right optic canal decompression. This surgery was performed endonasally with a four-hand technique similar to the description by Kassam et al (Kassam 2005). Extensive bone removal was required to access the intracanalicular segment of the right optic canal as the entire sphenoid sinus was replaced with dysplastic bone. Postoperatively, the patient has done well. For 2 months, he has not had any blurry vision and has complete resolution of the right optic nerve edema.

Conclusion: FD of the skull base is a challenging problem that can lead to cranial neuropathies and functional loss; in this case optic neuropathy and visual impairment occurred. Endonasal surgery can be useful for optic nerve decompression in the skull base.