Inflammatory Pseudotumor-like Follicular Dendritic Cell Tumor of the Spleen: Case Report and Review of the Literature.

A 74-year-old woman underwent contrast-enhanced (CE) computed tomography (CT) that revealed an enlarging splenic lesion. This splenic tumor was suspected as metastasis because the patient had been diagnosed with right breast cancer with lung and right axillary lymph node metastases 4 years earlier and had undergone surgery and hormone therapy at another hospital. T2-weighted imaging of magnetic resonance (MR) imaging demonstrated the tumor with slightly high intensity with a rim of low intensity at the margin. On dynamic contrast-enhanced (DCE)-MR imaging after intravenous administration of gadolinium diethylenetriamine pentaacetic acid, delayed enhancement was observed in the center and margin of the tumor. On positron emission tomography with 2-deoxy-2-[18F] fluoro-D-glucose (FDG) integrated with CT, the tumor showed high FDG uptake. Splenic metastasis was considered based on the imaging findings, lack of inflammation on laboratory data, and clinical course, so she underwent splenectomy. Histopathologically, the tumor was encapsulated by a fibrous structure, which was depicted as the rim at the tumor margin on T2-weighted imaging and DCE-MR imaging. Immunohistochemical study allowed the diagnosis of inflammatory pseudotumor (IPT)-like follicular dendritic cell tumor (FDCT). FDCT is a primary neoplasm of lymph nodes that shows features of follicular dendritic cell differentiation, and it is rare at the spleen. Differential diagnosis is difficult between IPT-like FDCT and similar splenic tumors, such as IPT, splenic metastases, hamartoma and hemangioma. However, in addition to the enhancement pattern within a tumor on DCE-MR imaging, detection of the capsular-like rim on MR imaging might aid the diagnosis of splenic IPT-like FDCT.