Splenic inflammatory myofibroblastic tumor (inflammatory pseudotumor) - A clinicopathologic and immunophenotypic study of 12 cases

Context.-Inflammatory pseudotumor is an uncommon and enigmatic lesion. The spindle cells found in this tumor have features of myofibroblasts. Because of the indefinite relationship of these lesions with inflammatory fibrosarc oma and their indefinite biologic behavior, inflammatory pseudotumor is cur rently classified as inflammatory myo fibroblastic tumor (IMT). To date, on ly case reports or small series have been published on these tumors, which are primary in the spleen. Design.-In this study, we describe the clinical, morphologic, and immunophe notypic findings of 12 cases of splenic IMT and examine their relationship to Epstein-Barr virus (EBV). Results.-The patients included 8 women and 3 men, ranging from 19 to 77 yea rs of age (mean, 53 years; median, 60 years). Demographic data were unavail able for 1 patient. Patients generally presented with abdominal pain (n = 5 ) and fever (n = 4). Associated lesions included renal cell carcinoma (n = 2), colonic adenocarcinoma (n = 1), and cholecystitis (n = 1). All tumors w ere composed of a bland spindle cell proliferation in association with a va riable mixed inflammatory component. There were 2 growth patterns, namely, a cellular spindle cell pattern and a hypocellular fibrous pattern. An immu nohistochemical panel confirmed the myofibroblastic nature of the spindle c ells. The spindle cells of 2 cases were immunoreactive for EBV latent membr ane protein 1, whereas 6 of 10 cases were positive for EBV-encoded RNA usin g in situ hybridization. Follow-up was available for 8 patients; 6 were ali ve with no evidence df recurrence and 2 were dead of other causes. Conclusion.-Splenic IMTs are uncommon lesions that can be distinguished fro m other conditions using a combination of clinical, histologic, and immunop henotypic findings. Epstein-Barr virus may play a role in the pathogenesis of splenic IMT, and there may be an association of splenic IMT with concomi tant disease or malignancy. Most splenic IMTs have an excellent long-term p rognosis.