Neurotized nevi of the oral mucosa: an immunohistochemical and ultrastructural analysis of nevic corpuscles

Abstract

Background: Nevic corpuscle (NC), a stacked lamellar structure reminiscent of Meissner corpuscle, is frequently observed in dermal melanocytic nevi. Although the heading ‘neurotized’ is classically used for these nevi, the exact neural nature of NC has been a topic of considerable debate. Neurotized nevi have received little attention in the dental literature, and there was no information on NC in oral melanocytic nevi. Methods: Six cases of oral intramucosal nevi with a significant number of NC (two completely and four partially neurotized nevi) were examined immunohistochemically and ultrastructurally. Results: NC was composed of closely piled laminar cells devoid of visible melanin. NC and associated spindle nevus cells were immunopositive for S‐100 protein but negative for HMB‐45, myelin basic protein and epithelial membrane antigen. Within NC, no reactivity for neurofilament protein, protein gene product 9.5 or peripherin was evident. Numerous CD34‐positive dendritic cells were located between nevus cells and often encircled NC. Ultrastructurally, NC consisted of concentrically layered elongated cells with a slender lamellated cytoplasm rich in thin filaments and pinocytotic vesicles. Their cytoplasmic processes were focally covered by external basal lamina and continuous to spindle nevus cells. Occasional NC cells contained a few melanosomes. There was no interposed axon in NC. Conclusions: Despite the close resemblance to Meissner corpuscle, NC showed no axonal supply. NC cells lacked terminal Schwannian differentiation and appeared to be modified melanocytes with some perineurial ultrastructural characteristics. The presence of CD34‐positive cells, presumably corresponding to endoneurial fibroblasts, further supports an organizational relationship of NC and peripheral nerve sheath elements.

CD34‐reactive tumors of the skin. An updated review of an ever‐growing list of lesions

“…CD34/ CD31 expression closely parallels tumor progression and parameters related to aggressive behavior. 139 CD34 reactivity has also been shown in melanocytic cells of some congenital cellular blue nevi, 140 in endoneurial fibroblasts of the nevic corpuscles of neurotized nevi 141 and in stromal cells of neurocristic hamartomas. 142 Fig.…”

“…CD34 reactivity has also been shown in melanocytic cells of some congenital cellular blue nevi, 140 in endoneurial fibroblasts of the nevic corpuscles of neurotized nevi 141 and in stromal cells of neurocristic hamartomas 142 …”

Oral plexiform schwannoma with unusual epithelial induction

“…In this case, we considered the neuroma group at first; however, neuromas, whether traumatic, palisaded encapsulated or multiple mucosal, are rich in axons and perineurial cells . CD34‐positive endoneurial fibroblasts are also acknowledged to be another constituent . The absence of axonal and perineurial elements as well as reactivity for GFAP set this tumor apart from a ‘true’ neuroma .…”

Spindle cell melanocytic lesions—part I: an approach to compound naevoidal pattern lesions with spindle cell morphology and Spitzoid pattern lesions

“…Occasionally, the neurotisation may be complete or near-complete, making differentiation of the lesion from a neurofibroma difficult 30 31. Nerve fascicle-like or even Verocay body-like structures may be observed in occasional cases 58. Immunohistochemical staining for myelin basic protein, CD57 or glial fibrillary acid protein may be discriminating features in uncertain cases, with positivity favouring neurofibroma or possibly another neural lesion 21 58.…”

“…More specific melanocytic markers are generally not preserved in type C naevomelanocytes, as they typically do not exhibit melanosomes or tyrosinase activity 35. Ultrastructurally, neurotised naevic cells do not show true Schwannian differentiation because of a lack of axonal or mesaxonal structures, and may reveal the rare melanosome 34 57 58. Overall, neuroidal naevi generally are not clinically concerning, and show an overall naevoidal pattern lacking any atypical cytological or architectural features, and so are easily recognised as benign.…”