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

OBJECTIVE. The objective of this study was to assess the imaging features of follicular dendritic cell sarcoma (FDCS) on CT and MRI. MATERIALS AND METHODS. The clinical data and pretreatment findings of 20 patients with pathologically proven FDCS on CT (n = 15), MRI (n = 7), or both (n = 2) were analyzed retrospectively. Tumor location, number, size, morphology, attenuation or signal intensity, margin, presence of metastases, and contrast enhancement were evaluated. RESULTS. FDCS originated from lymph nodes (n = 6) or a variety of extranodal sites (n = 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 (n = 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 (n = 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 (n = 4) and distant metastases (n = 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. CONCLUSION. 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.