Perineurioma versus meningioma. A multi-institutional immunohistochemical and ultrastructural studY

The differential diagnosis between perineurioma (PN) and meningioma (MEN) can be difficult by histology and immunohistochemistry (IHC) because the perineurium and arachnoid have the same embryological origin. However, there are no comparative studies determining conclusive parameters for the differential diagnosis. The aim of this study is to compare IHC of PN and MEN and their ultra-structural characteristics to elucidate which are the useful data that allow differentiate both entities. Thirty-five MEN were analyzed, and 15 PN, (11 skin and soft tissues and four oral cavity). IHC for epithelial membrane antigen (EMA), Claudin-1, GLUT-1, somatostatin-2 receptor (SSTR-2), and progesterone receptor (RP) was performed. Ultrastructural studies were performed on 8 MEN and 15 PN. Only in PN Claudin-1 was positive in 9/11 (90%) cases and GLUT-1 in 7/11 (63%) cases. In MEN, the progesterone receptor was expressed in 21/35 (60%) cases and no case expressed Claudin-1 and GLUT-1; EMA was expressed in all MEN cases and 93% of PN. SSTR-2 was expressed weakly in six cases of MEN (17%), and it was not considered useful for differential diagnosis. On ultrastructure, PN showed thin and parallel processes, some caveolae, and lacked cell junctions. The cellular processes were surrounded by a collagenous stroma in 94% of the cases. MEN were characterized by curved cytoplasmic cell processes showing desmosomes in 75% of cases. Ultrastructural findings aid in the differential diagnosis between PN and MEN, especially if molecular studies are not available.