Immunohistochemical Study of Inflammatory Pseudotumors of the Orbit at Farabi Hospital, Tehran, Iran

To verify the myofibroblastic origin of spindle cells by immunohistochemistry in idiopathic inflammatory pseudotumor (IPT) of the orbit. We reviewed a series of 32 orbital IPTs for expression smooth muscle actin (SMA), Vimentin, Desmin and anaplastic lymphokinase (ALK). The study was performed on histologic samples of 33 patients with a diagnosis of orbital IPT. The lesions expressed SMA in 51.7%, Vimentin in 72.0% and Desmin in 17.2%. All lesions were negative for ALK. Reactivity for SMA in spindle cells may indicate their myofibroblastic origin. The absence of ALK expression in all cases strongly suggests that these lesions, although histologically similar, are biologically distinct from their soft tissue counterparts. IPTs which are negative for ALK may be characterized by one or more chromosomal aberration involving regions other than 2p23