Follicular Dendritic Cell Sarcomas: CT and MRI Findings in 20 Patients.

Abstract

<b>OBJECTIVE.</b> The objective of this study was to assess the imaging features of follicular dendritic cell sarcoma (FDCS) on CT and MRI. <b>MATERIALS AND METHODS.</b> The clinical data and pretreatment findings of 20 patients with pathologically proven FDCS on CT (<i>n</i> = 15), MRI (<i>n</i> = 7), or both (<i>n</i> = 2) were analyzed retrospectively. Tumor location, number, size, morphology, attenuation or signal intensity, margin, presence of metastases, and contrast enhancement were evaluated. <b>RESULTS.</b> FDCS originated from lymph nodes (<i>n</i> = 6) or a variety of extranodal sites (<i>n</i> = 14). The tumors were typically solitary and well-circumscribed. Extranodal lesions (mostly in the abdomen or mediastinum with mean diameter, 11.8 cm) were larger than nodal lesions (mean diameter, 6.5 cm). Nodal-type cases presented with homogeneous masses on CT and MRI. However, on CT, all extranodal tumors (<i>n</i> = 12) showed heterogeneous attenuation, of which 91.7% (11/12) contained areas of lower attenuation because of internal necrosis and 50.0% (6/12) showed calcifications. On MRI, primary hepatic or splenic tumors (<i>n</i> = 3) also appeared as large heterogeneous masses. Seven patients (35.0%) had advanced-stage disease, and intraabdominal extranodal cases were more likely to have regional lymphadenopathy (<i>n</i> = 4) and distant metastases (<i>n</i> = 5). Hypervascularity was seen in 90.0% (18/20) of patients and progressive enhancement was seen in 11 (78.6%) of 14 tumors with multiphase imaging. <b>CONCLUSION.</b> FDCS is a rare, mostly solitary, well-delineated malignancy. A nodal-type FDCS typically presents as a small homogeneous mass, whereas an extranodal FDCS in the mediastinum or abdomen manifests as a large heterogeneous mass with internal necrosis and calcifications accompanied by regional lymphadenopathy. Hypervascularity and progressive enhancement can be seen in the majority of tumors.