Several proposed methods include the greatest dimension of the invasive tumor, the aggregate linear length, the depth of invasion (by millimeter measurements or using high-power fields), the anatomic level of involvement (based on its relation to the muscularis mucosa and the vascular plexus), and the percentage of invasive tumor.
The method of pT1 substaging has not been optimized, but microinvasive disease has been defined by different groups as invasive tumor of <1 high power field, greatest invasive tumor diameter of 1 mm, or invasive tumor above the muscularis mucosa extending to a depth of 2 mm or less.
The typical magnetic resonance imaging findings of the disease include a hypointense mass on T2-weighted images due to induced fibrosis and hypertrophy of the muscularis mucosa with or without hyperintense hemorrhagic foci on T1-weighted images with fat suppression, abutting the bowel wall (Fig.).
The severity of colonic injury was evaluated by the following parameters : epithelial damage (0, normal; 1, minimal loss of goblet cells; 2, extensive loss of goblet cells; 3, minimal loss of crypts and extensive loss of goblet cells; and 4, extensive loss of crypts); and infiltration (0, normal; 1, infiltrate around crypt bases; 2, infiltrate in muscularis mucosa; 3, extensive infiltrate in muscularis mucosa with edema; and 4, infiltration of submucosa).