Pneumatosis coli consists of gas-filled cysts within the bowel wall. Pneumatosis is asymptomatic or accompanied by constipation or diarrhea. The lesion may also be detected endoscopically or radiographically. Most often colonic disease follows mucosal ulceration due to ischemia, necrotizing enterocolitis, infection, and other causes. In the colon it may present endoscopically as a small mucosal elevation or polyp. It may also present as an intussusception (547). The cysts are found in all bowel layers. They are lined by epithelioid macrophages, multinucleated giant cells, and a variable chronic inflammatory cell infiltrate. An exceptional example of cysts containing spirochetes in a patient with coexisting spirochetosis was recently reported.