Contributors: Roger E. McLendon and David S. Enterline
Neurofibromatosis was recognized as a familial entity by Akenside in 1768, but the classic description of the condition was provided by von Recklinghausen in 1882. Neurofibromatosis type I is inherited as an autosomal dominant disorder and its cardinal manifestations are multiple plexiform neurofibromas, numerous café au lait spots, and Lisch nodules. Asymptomatic Lisch nodules are present in more than 90% of patients who are older than 6 years. Other manifestations include thickened nerves.The disease is caused by mutations of the NF1 gene which encodes for a poorly understood protein (neurofibromin).
Patients develop neurofibromas in many tissues (including eyelid, conjunctiva, cornea orbit) and have an increased risk of some other tumors (including pilocytic astrocytomas of the optic nerve and other parts of the central nervous system, malignant primary nerve sheath sarcomas that typically arise within preexistent plexiform neurofibromas, pheochromocytomas; multiple mature peripheral ganglioneuromas [particularly of the gastrointestinal tract]; and duodenal carcinoid tumors) as well as dysplastic lesions of the central nervous system.
Patients with neurofibromatosis type 1 are prone to juvenile pilocytic astrocytoma of the optic nerve, meningioma, as well as neurofibroma, schwannoma and malignant peripheral nerve sheath tumor in the orbit and in other sites.
Figure 1. Optic glioma in neurofibromatosis type I. There is a homogenously enhancing oval intraconal mass of the left orbit. This is an optic nerve mass and involves the optic nerve head through the region of the orbital apex. This is a typical appearance for optic glioma. Note also the relatively hypoplastic left sphenoid wing. The combination of these two factors is diagnostic of neurofibromatosis type I. Notice the compression of the globe and proptosis on this side.
Imaging Discussion: Optic gliomas occur along the optic tract but are commonly seen in the intraorbital segment of the optic nerve. Enlargement of the nerve is the principal imaging finding. A variable number of these tumours will enhance, usually homogenously. Dural ectasia of the optic nerve sheath is frequently seen in patients with NF 1. Other findings of neurofibromatosis including hypoplasia of the sphenoid wing, as seen in this patient, need to be considered. Mild cases of optic glioma are often followed clinically and by imaging. MRI is preferred over CT for evaluation of the optic nerves due to its superior soft tissue detail.