Skip lesion

In contrast to UC, the pattern of inflammation in CD is described as discontinuous. Areas of inflammation are intermixed with areas of normal GI mucosa, resulting in characteristic skip lesions. Superficial aphthous ulcers may also develop in the GI mucosa. These ulcers may coalesce into larger linear ulcers, resulting in fissure formation as they increase in depth, giving rise to the characteristic cobblestone pattern observed upon examination of the mucosa. 

Ulcerative colitis is confined to the rectum and colon, causes continuous lesions, and affects primarily the mucosa and the submucosa. Crohn s disease can involve any part of the Gl tract, often causes discontinuous (skip) lesions, and is a transmural process that can result in fistulas, perforations, or strictures. 

Cross-sectional imaging is able to demonstrate transmural extent, skip lesions beyond severe luminal stenoses, and intraperitoneal extraintestinal complications. However, CT and MR imaging are inferior compared to enteroclysis in the depiction of early disease manifestations and of fistulas and sinus tracts [59]. 

Fig. 13.10a-c. Crohn s disease Skip lesions (arrow) in the terminal ileum and the transverse colon (a,b). Irregular wall thickening and stenosis of the transverse colon with pericolic fat stranding and flattening and disappearance of the haustra (arrow) (b). Virtual colonoscopy shows luminal narrowing and cobblestone pattern... 

The radiological findings of Crohn s disease of the distal duodenum are similar to those of the rest of the small bowel and terminal ileum, with skip lesions, cobble stoning, asymmetry, and in the more advanced stage of the disease, strictures causing eccentric narrowing. Other features of Crohn s disease such as sinuses, fistulas, sacculations, and inflammatory pseudopolyps are uncommon in the duodenum (Fielding et al. 1970 Levine 1987 Hizawa etal. 1994). 

---