Figures 18, 19. (18) CT scan obtained in a 37-year-old man with acquired immunodeficiency syndrome who developed PMC following antibiotic therapy demonstrates thickening of the ascending and proximal transverse colon with an irregular luminal surface. The distal transverse colon and the descending colon have been spared. (19) CT scan obtained in a 63-year-old man who presented with signs and symptoms of colon obstruction and had a history of sigmoid colon diverticulitis that had been treated with antibiotics shows a well-defined focal thickening of the sigmoid colon simulating colon cancer (arrows). Sigmoidectomy was performed, and pathologic findings were consistent with PMC. After sigmoid colon resection, PMC progressed to involve the entire colon, and the patient underwent partial colectomy.