Elsevier

Oral Oncology

Volume 40, Issue 9, October 2004, Pages 948-953
Oral Oncology

Comparative ultrastructural and immunohistochemical study of perineurioma and neurofibroma of the oral mucosa

https://doi.org/10.1016/j.oraloncology.2004.04.015Get rights and content

Summary

In the course of assessing the cellular composition of intraoral neurofibroma (NF), we encountered a unique gingival tumor of putative perineurial (PN) origin. The lesion showed the ordinary light microscopic NF pattern, but the ultrastructural features of well-differentiated PN cells as well as an epithelial membrane antigen (EMA)-positive, S-100 protein-negative immunoprofile confirmed the diagnosis of soft tissue perineurioma (STP). In our small series of NF, there were three ultrastructural subtypes: Type I (common Schwann cell type), Type II (NF with a high content of PN cells) and Type III (predominantly fibroblastic NF), although inhomogeneous and overlapping assembly of cellular elements. A significant number of tumor cells in Type II showed the substantial reactivity for EMA, whereas many CD34-positive cells were noted in Type III. The present results confirm previous findings that PN lineage is an important constituent in the formation of NF and reinforce the value of electron microscopy in the diagnosis of peripheral nerve sheath tumors.

Introduction

Peripheral nerves consist of axons and ensheathments. Nerve sheath compartment is organized into three layers: endoneurium, perineurium and epineurium. They contain an assorted number and forms of supportive cells, including Schwann, perineurial (PN) and fibroblastic cells. A functionally specialized perineurium lies at the interface between the axon-Schwann cell units-investing endoneurium and a fibrovascular epineurium.1 PN cells differ from the inner most Schwann cells at the ultrastructural level by virtue of their long thin, bipolar cytoplasmic processes, numerous pinocytotic vesicles, discontinuous basal lamina, subplasmalemmal electron-dense plaques and well-developed tight junctions.[2], [3], [4] An epithelial membrane antigen (EMA)-positive immunophenotype is also accepted as additional evidence of PN differentiation in the setting of S-100 protein negativity.[1], [4], [5] These unique characteristics are never associated with endoneurial fibroblasts.1

Theoretically, neoplastic proliferation may occur independently from Schwann, PN or endoneurial fibroblastic cells; however, most peripheral nerve sheath tumors are undoubtedly schwannian in nature.1 Besides the two main forms, schwannoma and neurofibroma (NF), the term perineurioma, a third category of nerve sheath tumor entity, was advanced recently.[1], [5], [6] Because of the genuine rarity and considerable difficulty in the diagnosis, the existence of intraoral lesions does not appear to be widely appreciated.[7], [8], [9], [10], [11], [12] The purpose of the present study is to review the ultrastructure of gingival soft tissue perineurioma (STP) in some detail and to compare its cellular characteristics with classical NF which show a substantial participation of PN cells.[2], [3], [4], [5], [13], [14], [15], [16], [17], [18]

Section snippets

Materials and methods

STP case was a 59-year-old woman with a 2-month history of a painless, polypoid, soft nodule, 1.5 cm in greatest diameter, located on the palatal gingiva of the right upper first molar. Seven cases of intraoral solitary NF were available for comparative study. Formalin-fixed and paraffin-embedded sections were submitted for immunohistochemical analysis, including EMA (E29, 1:100; Dako, Glostrup, Denmark), S-100 protein (1:2000; Dako) and CD34 (My10, 1:100; Becton Dickinson, San Jose, CA).

Results

Submucosal STP presented with sharp circumscription but was not encapsulated on any side (Fig. 1(A)). The myxocollagenous tumor was composed of hypocellular interlacing fascicles of spindle to oval cells with wavy, wrinkled nuclei (Fig. 1(B)). There was no associated nerve within the lesion. Lesional cells showed diffuse membrane immunoreactivity for EMA (Fig. 1(C)), but were completely negative for S-100 protein and CD34. As shown in Fig. 2, tumor cells were spindle or stellate with irregular

Discussion

NF is formed by a complex proliferation of Schwann, PN, endoneurial fibroblastic and intermediate cells.[1], [4], [13], [14], [15], [16], [17], [18] With an average of about 36%,18 up to 87% of lesional cells were schwannian in nature.13 Although controversy exist regarding to what degree PN cells contribute to the formation of NF, they are an important neoplastic component.[2], [3], [4], [15] It is estimated that from 0.7% to 31% of the constituent cells were PN lineage.[13], [18] In a

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