Teaching Case

A 35-year-old patient with a known history of Neurofibromatosis type 1 (NF1) was referred for imaging because of a left sided strabismus and proptosis.

The patient had post intravenous contrast CT brain and orbits performed (See figures 1,2 and 3).

Neurofibromatosis type 1 (NF1) is a dysplasia of mesodermal and neuroectodermal tissue with the potential for diffuse systemic involvement. The condition is inherited in an autosomal dominant fashion with the abnormality localised to chromosome 17 and occurs in 1 in 3000 births. 50% of cases occur as the result of spontaneous mutations. The diagnosis of NF1 may be made clinically if two or more of the following 7 criteria are present: 1)>6 cafe-au-lait spots >5mm in greatest diameter, >15mm in postpubertal individuals. 2) 2 or more neurofibromas or one plexiform neurofibroma. 3) axillary/inguinal freckling. 4) Optic nerve glioma. 5) 2 or more lisch nodules. 6) Characteristic skeletal lesions. 7) First degree relative with NF1. The bony abnormalities classically associated with NF1 include sphenoid wing dysplasia, tibial pseudoarthrosis and scoliosis. (1) Sphenoid wing dysplasia is seen in approximately 7-11% of NF1 patients. It is always unilateral, and approximately 50% will have a clinically apparent plexiform neurofibroma of the temporal-orbital region. The bony defect may be associated with enlargement of the contents of the middle cranial fossa with herniation of the temporal lobe into the orbit. An arachnoid cyst is a frequent association. Exophthalmosis can occur secondary to the herniated structures at the posterior aspect of the orbit but is a rare complication that may require therapeutic management. (2, 3) Buphthalmos is also associated with NF1. It is believed to be caused by increased intraocular pressure because of obstruction to the flow of aqueous humor leading to enlargement of the globe. (4) Other authors believe that it may be a manifestation of regional gigantism. (5) The CT appearances show increased transverse and anterior to posterior diameter of the globe, thickening of the uveal/scleral layer and may be associated with anterior orbital plexiform neurofibromas.