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Figure 3a.   Recurrent large cell lymphoma in the right kidney in a 28-year-old man. The patient had undergone successful treatment of a large anterior mediastinal mass 7 months earlier. (a) Contrast material-enhanced helical CT scan obtained at the time of recurrence illustrates the sensitivity of this modality for the detection of very small lesions (arrowheads). (b) Contrast-enhanced CT scan obtained 6 weeks later shows that one of the lesions has increased markedly in size (arrow).