Plexiform and other unusual variants of palisaded encapsulated neuroma.

Palisaded, encapsulated neuroma (PEN) has been described as a predominantly solitary, nodular tumor; plexiform or multinodular growth patterns have not been reported in detail. We reviewed 55 PEN in order to evaluate: 1) the predominant growth patterns; 2) features that may indicate previous trauma; and 3) association with acne-like changes. Sixteen cases (29%) had growth patterns other than the solitary, nodular type. These patterns were: a) plexiform (7/16), b) multinodular (5/16), and c) fungating (4/16). Other unusual features included evidence of trauma, i.e., fibrosis, myxoid change, chronic inflammation (5/16), partially incomplete capsule (6/16), and association with acne-like features (13/16). These results suggest that: 1) plexiform or multinodular growth patterns occur relatively often in PEN; 2) some changes indicate a possible histogenetic relation to traumatic neuroma, probably via secondary traumatization; 3) a high frequency of association with acne-like changes which could imply, but does not prove, an acne-induced histogenesis; and 4) the differential diagnosis of cutaneous plexiform lesions should include PEN.