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Washington University Experience | NEOPLASMS - CRANIAL AND PARASPINAL NERVEs | Neurofibroma | 18C Denouement Case 18
Not shown: Histochemically stained sections show relatively uniform blue staining of collagen by trichrome stain throughout the tumor parenchyma, and red staining of a large subset of tumor cell nuclei and of axons both within and adjacent to the tumor. Reticulin stained sections show a pattern of reticulin fibers throughout the tumor that roughly corresponds to the distribution of blood vessels and Schwann cells, without distinct reticulin-poor areas. Immunohistochemically stained sections show reactivity for neurofilament protein (NF) that highlights axonal processes distributed sparsely within the tumor tissue, and at high density in uninvolved or modestly-involved nerve fascicles within the pseudocapsule; this pattern is consistent with infiltrative intrafascicular growth. Reactivity for collagen IV highlights the basement membranes surrounding a subset of, but not all, tumor cells, as well as basement membranes around blood vessels. Reactivity for S-100 protein highlights peripheral nerve tissue adjacent to and entrapped by the tumor, as well as Schwann cells and a subset of ganglion cells that appear within the tumor parenchyma. Nuclear reactivity for proliferation marker Ki67 is present at a density that ranges up to 6% of tumor cells. This histological/histochemical/immunohistochemical pattern is that of a neurofibroma with atypical features. ---- Comment: As this tumor shows increased proliferative index in the absence of the other worrisome features (areas of cellular crowding, markedly enlarged nuclei, hyperchromasia, necrosis, atypia, and increased proliferative index) the diagnosis of low grade malignant peripheral nerve sheath tumor is not appropriate. Nevertheless, close monitoring of this patient for local recurrence is prudent.
