Treated plasma cell lesions of bone with MRI signs of response to treatment : unexpected pathological findings

Two cases of treated plasma cell lesions of bone are reported for which contrast-enhanced MRI had suggested necrosis, based on lack of enhancement after gadolinium injection, and in which pathologic examinations revealed the presence of extensive viable neoplastic tissue. These cases highlight the need for cautious interpretation of contrast-enhanced MRI signs of response to treatment and inactivity of lesions in the setting of plasma cell neoplasms.