A 57-year-old man had noticed a right chest wall mass lesion for 15 years, but had ignored the lesion in the 5 years before presentation. He was admitted to our hospital without significant symptoms and with no history of tuberculosis. Magnetic resonance imaging (MRI) was performed, and a 5-cm-diameter lesion was found. The signal was isointense on T1-weighted imaging (T1WI) and hyperintense on T2-weighted imaging (T2WI) (Fig. 1). Needle biopsy was performed, and histopathology showed lymphocyte infiltration with no evidence of malignancy. The patient was followed up for the next 7 years, and during that interval he had no significant symptoms.  
On MRI after 7 years of follow-up, the primary chest wall mass lesion was without any significant change, but a small subcutaneous mass lesion was found nearby. The MRI signal of this subcutaneous mass was almost identical with the original mass (Fig. 2). Diffusion-weighted imaging (DWI) was performed and both lesions exhibited high signal on DWI and a low apparent diffusion coefficient (ADC) (about 0.5) on the ADC map (Fig. 3). In light of the MRI findings, hypercellular malignant tumors (including melanoma and lymphoma), atheroma, and nodular fasciitis were suspected. Excisional biopsy was not performed since that would make definitive re-excision more extensive due to the contamination of surrounding tissue planes. Therefore an open biopsy of both lesions was performed. The mass lesions were both found to be marginal zone B-cell lymphomas (Fig. 4).    
In this case, no other tumors were found, so radiation therapy only (36 Gy/20 French) was given. The patient was discharged, and follow-up found the patient in good condition with no apparent signs of recurrence after 2 years.