CT appearance of a prosthetic methyl methacrylate mass mistaken for abscess

A nonopaque methyl methacrylate mass that had the appearance of an abscess in a postoperative CT scan of the spine is described. Contained gas produced an attentuation range of +20 to -300 HU, with an average of -80 to -250 HU. This finding was confirmed by CT examination of a separate cement mass removed from a similar patient.