[504] Plexiform Spindle Cell Nevus: A Clinicopathologic Study of 122 Cases

Tawny Hung, Aparche Yang, Raymond L Barnhill. Vancouver General Hospital and University of British Columbia, Vancouver, BC, Canada; UCLA Medical Center, Los Angeles, CA

Background: Since its description, the proponents of plexiform spindle cell nevus (PlexiSCN) have emphasized its characteristic plexiform/fascicular architecture and predominant spindle cell phenotype. The authors have recently observed that angiotropism may further aid in the recognition and distinction of PlexiSCN from other melanocytic tumors.
Design: In this study, 122 PlexiSCN were evaluated for 21 clinical and histological parameters including angiotropism and/or neurotropism. Angiotropism and neurotropism were defined as melanocytes aligned along the external surfaces of blood vessels or nerves at the peripheries of the lesion. Additional tumor characteristics recorded for each lesion were: maximal diameter of the lesion (mm), symmetry, ulceration, circumscription, maturation, nodule formation, Breslow thickness (mm), Clark level, cell type, nevus/tumor components, configuration, mitotic rate (per mm2), presence of deep mitosis, significant cytologic atypia, recurrence or regrowth of tumor and positive margins.
Results: We found that the typical PlexiSCN architecture consisted of a symmetric, well-circumscribed plexiform/fascicular dermal melanocytic proliferation associated with angiotropism. PlexiSCN demonstrated a predominant spindled melanocyte phenotype. There were varying proportions of admixed epithelioid melanocytes, and the degree of melanocytic pigmentation differed slightly in each case. Melanocyte maturation was minimal; slight cytological atypia was characteristic. The mitotic rate was 0-2 per mm2 and deep dermal mitoses were rare. Angiotropism was present in 100% of cases and neurotropism was present in 46.7% (57/122). The majority of PlexiSCN were associated with a conventional nevus (55.5% (57/122)); 11.5% (14/122) occurred with a blue nevus; 4.1% (5/112) occurred with a Spitz nevus. 37.7% (46/112) of PlexiSCN were not associated with a secondary melanocytic neoplasm. Ten lesions fell outside the typical PlexiSCN morphology and were “unclassifiable.” One case was categorized as “atypical PlexiSCN.” We are not aware of any adverse outcomes from our reported cases but detailed outcome data will be reported.
Conclusions: By employing the strict criteria of plexiform/fascicular dermal configuration, angiotropism, predominant spindle cell phenotype, and absence of Spitz and blue nevi characteristics, the plexiform spindle cell nevus can be reliably recognized as a distinct entity.
Category: Dermatopathology

Monday, March 19, 2012 8:30 AM

Platform Session: Section F, Monday Morning

 

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