Inflammatory Pseudotumor in the Mediastinum: Imaging with 18F-Fluorodeoxyglucose PET/CT
A 25-year-old male had a chest X-ray taken as part of a routine health examination; the results showed a large mass in the right paratracheal space (). He had had acute lymphoblastic leukemia 11 years earlier but was in complete remission. He was asymptomatic, had no pain, cough, or dyspnea. His physical examination was normal, and all laboratory tests were within normal limits except mild leukocytosis (12.1 × 103/µL, normal range 3.9-9.7). Contrast-enhanced chest CT and 18F-FDG PET/CT were performed to rule out malignant lymphadenopathy (). The mass showed mild homogeneous enhancement with a longitudinal dimension of approximately 8.0 cm in the right paratracheal space in the transaxial view on contrast-enhanced chest CT (Brilliance CT 16-slice, Philips Medical Systems, Cleveland, OH, USA). No abnormality was observed in the lung parenchyma (). The patient underwent 18F-FDG PET/CT (Discovery STe scanner, GE Healthcare, Milwaukee, WI, USA) after fasting for at least 6 hours. Unenhanced CT was performed by a continuous spiral technique using a 16-slice helical CT (120 KeV, 80-200 mAs with AutomA mode, a section width of 3.75 mm) 60 minutes after injection of 370 MBq 18F-FDG. After CT scan, an emission scan was obtained from the thigh to the head for 3 minutes per frame in the 3-dimensional (3D) mode. Attenuation-corrected PET images using CT data were reconstructed by a 3D ordered-subsets expectation maximization algorithm (20 subsets, 2 iterations). A huge mass with lobulated borders was found in the right paratracheal space; the mean Hounsfield unit of the mass was 36 on unenhanced CT of 18F-FDG PET/CT. On PET images, the mass showed heterogeneous 18F-FDG uptake, with the maximum standardized uptake value (SUVmax) of 5.0 (). No 18F-FDG uptake suggesting metastases was observed on PET/CT.\nThese clinical and radiological findings suggested malignant lymphadenopathy associated with recurrent leukemia. The patient underwent mediastinoscopic biopsy. Histopathology suggested an inflammatory pseudotumor. The mass was removed via thoracotomy. The tumor was a multinodular mass, measuring about 8 × 6 × 5 cm. On the cut section, the mass was lobulated by intervening fibrous tissue, showing a yellow-brown or yellow-white color with a myxoid character. Histopathologically, the tumor contained multifocal patchy infiltration of B and T lymphoid cells, plasma cells, histiocytes, and fibroblastic cells in a fibrocollagenous stroma (). The final diagnosis was an inflammatory pseudotumor, fibrohistiocytic type.