Solitary extramedullary plasmacytoma (EMP) of the spleen is a rare condition. The present study describes the case of a 23-year-old female with an extremely rare solitary EMP of the spleen. Upon examination, the tumor demonstrated unusual and notable multiple-phase spiral computed tomography (CT) findings. The lesion was a solitary, well-defined mass, with areas of variable splenic necrosis and cystic degeneration. Contrast-enhanced CT revealed progressive enhancement of the lesion in the cystic wall, internal septa and solid portion, a finding that has not previously been described. The patient underwent a splenectomy and recovered without complications. No evidence of tumor recurrence has occurred during the past two years of follow-up. To the best of our knowledge, this is the first study to examine the CT findings of a solitary EMP of the spleen. The study aimed to investigate the imaging features of solitary EMP, in particular the multiple-phase spiral CT findings, and raise awareness of the disease to reduce misdiagnoses.