SOLITARY PLEXIFORM NEUROFIBROMA IS NOT PATHOGNOMONIC OF VON-RECKLINGHAUSENS-NEUROFIBROMATOSIS - A REPORT OF A CASE

A 42-year-old Caucasian man presented with a 1.8-cm nodule in the prox imal thigh (Fig. 1) that had been slowly enlarging for approximately 5 years. The patient had no family history of neurofibromatosis Physica l examination revealed none of the other stigmata oi this neurocutaneo us disorder. D.A.F. performed an elliptical excision as an out-patient procedure. Grossly, the lesion was homogeneously opalescent and gelat inous, The tissue was fixed in 10% formalin and embedded in paraffin. Routine hematoxylin and eosin stained sections were prepared. The most notable feature on low power magnification was a large, circumscribed , lobular proliferation of spindle cells in a loose fibrillar backgrou nd that distorted much of the dermis and subcutaneous fat (Fig. 2). On high power magnification, a population of cells with ovoid and S-shap ed nuclei admired within densely packed eosinophilic collagenous mater ial was seen at the center of the lobule (Fig. 3A). A small amount of mucin was also present. Within this cellular area, a dense population of S-shaped spindle cells with eosinophilic cytoplasm was arranged in a parallel array forming microfascicles. At the periphery of this cell ular component, a similar population of cells was arranged against a l oose fibrillar background of abundant mucin (confirmed by colloidal ir on stain) and scattered mast cells (Fig. 4). Lining the lobule was a c ompressed rim of thin, delicate collagen bundles and perineurial cells . Pleomorphic nuclei and mitotic figures were not observed. The surrou nding dermis and subcutaneous tissue were unremarkable. Thickened coll agen bundles at the center of the lobule could be seen with a trichrom e stain. An S-100 protein immunoperoxidase stain highlighted scattered Schwann cells within the lobule (Fig. 3B), and nerve bundles adjacent to the neurofibroma served as internal positive controls.