INTRODUCTION Plexiform neurofibromas are the most common benign peripheral nerve tumor occurring in the eyelid and are considered pathognomonic for type 1 neurofibromatosis (NF-1). The lesion arises from and grows along any peripheral nerve. Plexiform neurofibromas typically present in children during the first decade of life. Mechanical ptosis can be profound, and in younger children may cause deprivation amblyopia. Associated systemic and ocular findings in patients with neurofibromas are related to underlying neurofibromatosis. Systemic findings may include hamartomas of the CNS, and cranial and peripheral nerves. Patients are at increased risk of developing pheochromocytoma, breast carcinoma, medulllary thyroid carcinoma, and gastrointestinal tumors. Ocular findings may include iris nodules (Lisch nodules), glaucoma, retinal astrocytic hamartoma, optic nerve glioma or meningioma, pulsating exophthalmos due to defects of the sphenoid wing, and orbital schwannoma. Rarely an eyelid neurofibroma may be seen in segmental neurofibromatosis without systemic manifestations of NF-1.
CLINICAL PRESENTATION The plexiform neurofibroma often presents as a diffuse infiltration of the eyelid and orbit. The upper eyelid is involved in almost all cases and the lower lid in more than half. Brow infiltration is seen in about 20% of cases. The upper eyelid is usually ptotic and often develops an S-shaped curvature due to thickening and horizontal redundancy. On palpation the individual thickened nerves have the feel of a "bag of worms." Congenital glaucoma has been reported in some children with NF-1 and plexiform neurofibromas.
HISTOPATHOLOGY Plexiform neurofibromas are the most common form of eyelid neurofibroma. In plexi-form neurofibromas large segments of peripheral nerve become convoluted and appear like a "bag of worms" macroscopically. Microscopically there is a tortuous mass of expanded nerve branches, each surrounded by a perineurium. In early lesions, the nerve is swollen by endoneurial accumulation of myxoid (glycosaminoglycan-rich) matrix. As the lesions age, Schwann cells proliferate and collagen accumulates within the nerves.
TREATMENT Because of the infiltrative nature and vascularity of this tumor, therapeutic management is usually frustrating and disappointing. Recurrences are typical. Repeated surgical debulking may be necessary to maintain visual function and to offer some cosmetic improvement.
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