PET-MRI hybrid imaging in a rare case of B cell lymphoblastic lymphoma with musculoskeletal manifestation

Abstract

Dear Editor, A 44-year-old male presented with lower back pain radiating to both legs underwent magnetic resonance imaging (MRI) and was found to have a pathologic fracture of the L4 vertebra and an osteolytic lesion of the left sacrum with adjacent soft tissue infiltration. Apart from radiating back pain, the physical examination was unremarkable, the patient denied B-symptoms, and laboratory values including blood counts were within normal limits. CT-guided biopsy of the sacral lesion showed infiltrations of small blue round cells (Fig. 1a) with positive immunohistochemistry staining for CD99 (Fig. 1b), CD34, CD10, CD79a, CD56, nuclear PAX5 (Fig. 1c), and TdT (Fig. 1d); based on which, after initial suspicion of metastatic disease or Ewing sarcoma, B cell acute lymphoblastic leukemia was diagnosed. Karyotype was normal and molecular biology analysis did not detect any common ALL-associated aberration. Importantly, upon routine bonemarrow (BM) biopsy of the iliac crest, there was no evidence of malignancy, confirming localized disease. After spondylodesis between L3 and L5 for stabilization of the spine, staging was completed by positron emission tomography (PET)-MRI hybrid imaging, which we chose to screen for possible multifocal BM involvement, as seen in previous cases [1, 2]. T1(Fig. 1e) and T2-weighted short tau inversion recovery (STIR) MRI (Fig. 1f) revealed altered BM signal in the left proximal femur, acetabulum, and the left sacrum—with adjacent soft tissue infiltration, tumorous infiltration of the compressed L4 vertebra—with extra-osseous formations extending to the retroperitoneum and the aortic bifurcation-, as well as focal lesions in the right ischium and the transverse process of the T2 vertebra. [F] Fluorodeoxyglucose (FDG)–PET showed intense FDG uptake of the described lesions (Fig. 1g), with PET-MRI fusion images giving the best illustration of extent and localization of disease (Fig. 1h). Based on the immunohistochemistry findings, the mass lesions and a BM infiltration of <25 %, B lymphoblastic lymphoma (B-LBL) was diagnosed and the patient was started on chemotherapy according to the GMALL 07/2003 protocol, comprising an intense polychemotherapy protocol over 52 weeks with intrathecal chemoprophylaxis and prophylactic whole brain radiation. Interim staging after induction II by PET-CT showed complete remission (CR). Given the absence of risk factors, the patient was not planned for allogeneic transplant and followed the GMALL protocol over the scheduled time, remaining in CR 1 year after initiation of treatment. R. Eichner : C. Peschel : F. Bassermann : I. Ringshausen (*) III. Department of Internal Medicine, Klinikum rechts der Isar, Technische Universitat Munchen, Ismaninger Strase 22, 81675 Munich, Germany e-mail: i.ringshausen@lrz.tum.de