Perineuriomatous nevi: A series of eight cases highlighting unifying pathologic features to avoid misdiagnosis.
BACKGROUND
Perineuriomatous nevi are rare and diagnostically problematic. We report a series of eight perineuriomatous nevi to highlight the diagnostic features.


METHODS
Cases were retrospectively reviewed and characterized.


RESULTS
Median age was 42.5 years (range 25-64), with equal sex distribution. Lesions occurred on the arm (n = 4), trunk (n = 2), and head/neck (n = 2). Median size was 7.5 mm (range 5-12 mm). Clinical differential diagnoses included atypical nevus (3), blue nevus (1), neurofibroma (1), and dermatofibroma (1). Lesions were circumscribed, dome-shaped (5/8), and biphasic (8/8) with nested epithelioid cells and wavy spindled cells arranged in whorled fascicles in a myxocollagenous stroma. When present, junctional growth was lentiginous (4/8). No cases displayed pleomorphism or mitotic figures. The perineuriomatous component stained positively for epithelial membrane antigen (8/8 focal to diffuse) and CD34 (4/5 focal to diffuse). SOX10 and S100 protein stained all nevoid cells and in some cases a subset of intermingled spindled cells in perineuriomatous areas, where other melanocytic markers were negative. p16 protein expression was uniformly retained (3/3), and p53 negative (0/2). Nevoid cells in most lesions were positive for BRAFV600E (5/7). Ki67 was mildly elevated (~5%) in 3/3 cases.


CONCLUSIONS
Recognizing the histopathologic and immunophenotypic features in these unusual nevi helps avoid overdiagnosis.
['McAfee|John L|JL|https://orcid.org/0000-0001-7645-631X', 'Dermawan|Josephine K|JK|https://orcid.org/0000-0002-1139-2914', 'Billings|Steven D|SD|https://orcid.org/0000-0002-2278-5908', 'Ko|Jennifer S|JS|https://orcid.org/0000-0003-0629-775X']
perineuriomatous nevus melanocyte desmoplastic melanoma immunohistochemistry perineurioma