Fig. 3. Axial T1-weighted gadolinium-enhanced magnetic resonance image of the lumbar spinal cord before and after initiation of morphine (12.5 mg/ml at 40 μl/h) infusion for 31 days. Small masses (  arrows ) were reliably observed by 3 days and were substantial at 10 days. At 31 days, the pump was refilled with saline, and infusion continued for 14 more days. By day 7–8 of saline, the masses were reduced in size and continued to decrease in size but were still visible by day 14.