Purpose: To present the clinical, radiologic, and histopathologic features of orbital primitive neuroectodermal tumor (PNET) in 5 adult patients. Methods: Retrospective case series of 5 adult patients with orbital PNET. Orbitotomy was performed in all cases. The authors report clinical findings, radiologic features, histopathology, immunohistochemical analysis, management, and outcomes for 5 patients with orbital PNET. Results: Five adult patients presented with progressive unilateral proptosis and visual impairment. Common radiographic findings included a heterogeneous mass without associated destructive features, located in the superior and/or lateral orbit. Four cases demonstrated strong immunohistochemical staining for CD99 in a membranous pattern. One case required chromosomal analysis with fluorescence in situ hybridization to confirm the diagnosis. All patients received chemotherapy and/or orbital radiation with resolution of proptosis but no improvement of vision. One patient died of disease. Conclusions: To the authors' knowledge, this is the largest series of orbital PNET in adults. This tumor has an age demographic wider than previously believed and should be considered in the differential diagnosis of a hypercellular small round cell orbital tumor in both children and adults. Current treatment regimens are not standardized but typically use a similar approach to the treatment of Ewing sarcoma. Orbital PNET appears to have less propensity for metastasis compared with PNET in other locations. However, long-term aggressiveness remains to be proven.
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