[Perivascular myoma: a new concept for "myofibroblastic" tumors with perivascular myoid differentiation]

The morphological spectrum of cutaneous adult myofibroma (AM) is presented which has been considered to be the adult counterpart of infantile myofibromatosis. 63 cases of AM were evaluated and various subtypes could be discerned: classical biphasic type with hyalinized basophilic spindle cell nodules and adjacent small primitive pericytic cells forming richly vascularized hemangiopericytomatous sheets; glomangiopericytoma with a predominant hemangiopericytomatous pattern and small glomoid-pericytic cells; myopericytoma with angiocentric proliferation of small pericytic cells; rare variants, e.g. solid myopericytoma, and sclerotic myofibroma. There is considerable morphological overlap, and the morphological spectrum certainly is much wider. It is suggested that these presumably myofibroblastic cutaneous tumors are derived from a pluripotent periendothelial cell capable of differentiating along smooth muscle, pericytic, and glomus cell lines. Following a recent proposal by Granter et al. (7) these tumors are re-classified as variants of perivascular myoma, a perivascular tumor with myoid differentiation. The role of the myofibroblast in these tumors is reevaluated. In order to determine whether perivascular myoma is composed of a clonal cell population as opposed to being a polyclonal reactive process, analysis of patterns of X-chromosome inactivation was performed. Clonality of the tissue was determined by analysing the methylation status of two different X-chromosome linked polymorphic markers: the phosphoglycerate kinase gene (PGK) and the human androgen receptor gene (HUMARA). Both methods are based on the amplification of differing gene loci in heterozygous women after digestion of the DNA with methylation sensitive restriction enzymes. Out of 20 investigated female tumors 10 tumors were non-informative, 7 tumors showed a uniform pattern of X-chromosome inactivation (clonal), 3 tumors remained heterozygous (polyclonal). It remains to be determined whether perivascular myoma is a true tumor or a reactive/hyperplastic process.