The relationship between palisaded encapsulated neuroma and the mucocutaneous neuroma seen in multiple endocrine neoplasia 2b syndrome: a histopathologic and immunohistochemical study.

A relationship between the palisaded encapsulated neuroma (PEN) and the mucocutaneous neuroma seen in multiple endocrine neoplasia (MEN) 2b syndrome has been noted. We experienced a case of multiple mucocutaneous neuromas including both MEN 2b type neuromas and PENs. We evaluated the histopathologic and immunohistochemical features of 48 lesions in this patient. The lesions were histopathologically classified into 3 groups: (1) MEN 2b type neuroma (18 lesions), (2) PEN (22 lesions), and (3) an intermediate form of the 2 conditions (8 lesions). The intermediate form was classified into 2 subtypes: 1 type characterized by PEN nodules made up of assembled neuroma fascicles neighboring MEN 2b type neuroma fascicles and the other type characterized by more broad nerve fascicles than those seen in typical MEN 2b type neuroma. The idea that PEN is a progressive form of MEN 2b type neuroma may be speculative. Instead, the present study suggests that the observation of hybrid MEN 2b type neuroma/PEN in association with MEN 2b type neuroma and PEN may be a characteristic finding in cases of multiple mucocutaneous neuromas. The view that MEN 2b type neuroma and PEN lie within a spectrum of the same disease entity may be an overstatement; however, the present study suggests that PEN is basically a neural hamartoma/benign neoplasm, like MEN 2b type neuroma, and that there is a close relationship between the 2 conditions in terms of their histogenesis.