What are the causes of large bowel wall thickening on MDCT?
Wall thickening is present in numerous conditions, including Crohn’s, ischemic colitis, pseudomembranous colitis, radiation colitis, neutropenic colitis, and infectious (cytomegalovirus or Campylobacter ) colitis. On CECT, wall thickening can present either as homogeneous enhancing soft-tissue density or as concentric rings of high attenuation from hyperemic enhancement of the mucosa and serosa surrounding the low attenuation of the nonenhancing submucosa, termed the halo or target sign.
The cause of wall thickening sometimes can be determined by location or associated findings. For example, wall thickening in the splenic flexure region suggests ischemic disease from hypoperfusion in the superior mesenteric artery (SMA) and inferior mesenteric artery watershed area. Inflammation from a ruptured appendix can produce wall thickening mimicking a primary cecal process, and severe pancreatitis can cause transverse colon wall thickening if inflammatory changes spread through the transverse mesocolon.
Adenocarcinoma can present with an annular narrowing, an intraluminal polypoid mass, or eccentric lobulated wall thickening. Findings of regional or retroperitoneal adenopathy or liver or lung metastases help confirm the diagnosis of carcinoma. Signs of extracolonic extension include strands of soft tissue extending into the pericolonic fat, loss of fat planes between the colon and surrounding structures, and a masslike appearance. CT is useful in evaluating anastomotic recurrence from colorectal carcinoma, which occurs in the serosa, beyond the reach of the endoscope.