Hemangiopericytoma With Cartilaginous Differentiation Involving Orbit

Abstract

This rare tumor which contains a combination of mesenchymal elements is believed to be the only one of its kind appearing in the orbit. The mesenchymoma has been described in detail by Stout.^1,2 These tumors which are derived from mesenchyme appear microscopically to arise from supportive and reticuloendothelial tissues. Stout¹ believes that most of the mixed mesenchymal tumors are probably initiated as the result of a developmental fault and so are regarded as dysontogenic growths. He believes that metaplasia plays some part in their development. There has been considerable discussion regarding this tumor, for it demonstrates two tissues arising from basic mesenchyme. The principal one represents a hemangiopericytoma, in which the tumor cells are believed to arise from the pericyte of Zimmerman and lie outside the reticulum sheath of the capillary, differentiating it from the hemangioendothelioma.³ In addition, there appears in this tumor a growth of chondroblastic