Isolated neurofibroma of the orbit with extensive myxoid changes: a clinicopathologic study including MRI and...

Isolated orbital neurofibroma (INO) without systemic neurofibromatosis is rare. Previous reports including MRI with elaboration of the ultrastructural features of the cellular and extracellular components in INO do not exist. A 44-year-old male presented with painless, slowly progressive proptosis (6 mm) and downward displacement (3 mm) of the left eye of two years duration. MRI revealed a suprabulbar mass hypointense to fat, isointense to brain on T1-weighted images with small hyperintense areas following contrast enhancement. T2-weighted images showed a predominantly hyperintense mass with a few hypointense islands. The lesion was excised using an anterior superior transseptal orbitotomy. Histopathologically, large areas of a paucicellular myxoid stroma containing mucopolysaccharides made up approximately three-quarters of the mass. Focal hypercellular areas showed marked collagen deposition. Blood vessels were distributed at the periphery of the lesion and in association with nodules of nerve sheath cells. Ultrastructurally, perineural and fibroblast-like cells were loosely arranged in a myxoid stroma. Schwann cells were embedded in a dense collagenous matrix. Variable differentiation of Schwann cells, perineural cells and fibroblast-like cells associated with a more solid (collagenous) or loose (myxoid) extracellular matrix may determine the characteristic, though not specific, MRI features in isolated neurofibromas of the orbit.