&p.1:Abstract Objective. To evaluate the signal characteristics of primary non-Hodgkin’s lymphoma of bone on MRI. Designs and patients. Ten patients with primary non-Hodgkin’s lym- phoma of bone were included in the study. T1- and T2-weighted imaging was performed. The signal intensity of the lesions was compared with that of the surrounding muscle. Results. The results of the MRI were compared with the histological find- ings. In the majority of cases (5/10) the lesion involved the femur. In one case each the tibia, humerus, ileum, sacrum, and skull, respectively, were affected. A soft tissue mass was present in four cases. In nine of ten cases on T1-weighted imaging the lesion was hypointense. On T2- weighted imaging seven of ten le- sions were hypointense compared with muscle, one isointense and, in two cases, part of the lesion showed slightly hyperintense signal. In all ten cases the signal pattern appeared inhomogeneous. Pathological exami- nation showed extensive fibrosis in the majority of cases. Conclusion. According to our results there is decreased signal intensity of bone marrow on both T1- and T2- weighted imaging, unlike other pri- mary round cell tumors of bone. Be- cause the diagnoses were established with small tissue biopsies, the reason for these findings is speculative. &kwd:Key words Lymphoma · MRI in non-Hodgkin’s lymphoma · Signal characteristics in non-Hodgkin’s lymphoma&bdy: Skeletal Radiol (1997) 26:629–632 © International Skeletal Society 1997 ARTICLE MRI appearance of primary non-Hodgkin’s lymphoma of bone &roles:George Hermann Michael J. Klein Ibrahim Fikry Abdelwahab Samuel Kenan Introduction Primary bone lymphoma is a rare tumor, accounting for approximately 3% of primary malignant bone tumors and for 5% of extranodal lymphomas [1]. In the majority of cases the tumor involves the extremities and less fre- quently the axial skeleton. The patients usually present with localized mild pain, occasionally with soft tissue swelling that may have lasted for a year or longer. The differentiation from other primary round cell tumors of bone is sometimes clinically difficult. The radiological findings are nonspecific. A lytic lesion is generally pres- ent with a permeative pattern and occasionally with a soft tissue mass. Primary lymphoma of bone has a better prognosis than other round cell tumors of bone or dis- seminated non-Hodgkin’s lymphoma with skeletal in- volvement. In order to evaluate the specificity of MRI in differentiating primary lymphoma from other tumorous lesions we reviewed the MR appearance and correlated the image pattern with the histopathological findings. Materials and methods We retrospectively reviewed ten patients with primary non-Hodg- kin’s lymphoma who were referred to our institution for diagnosis and/or therapy. Seven of the patients were male, three female. The patients ranged in age from 17 to 75 years, with a mean age of 45 years. Patients with primary round cell tumor of bone were used as control. The images of all the cases were reviewed by two of the authors independently (G.H., I.F.A). In all cases the patients complained of local pain and discom- fort that had lasted from several months to 1 or 2 years. In every instance a single lesion was demonstrated, and neither regional G. Hermann, M.D. ( ✉ ) I.F. Abdelwahab, M.D. Department of Radiology, Box 1234, Mount Sinai Medical Center, One Gustave L. Levy Place, New York, NY 10029–6574, USA M.J. Klein, M.D. Department of Pathology, Mount Sinai Medical Center, New York, NY 10029–6574, USA S. Kenan, M.D. Hospital for Joint Diseases, 301 East 17 th Street, New York, NY 10003, USA&/fn-block: