OMED E-Newsletter Issue 4, 2009: Brainteaser/image of the month
This lesion was found in the sigmoid colon of a 72 year-old man undergoing colonoscopy after faecal occult blood testing was positive.
What is the most likely endoscopic diagnosis?
- adenoma with low or moderate dysplasia
- hyperplastic polyp
- serrated adenoma
- adenoma with high grade dysplasia or at the most intramucosal cancer
- invasive carcinoma
Explanation
The correct answer is d). This 6-7 mm lesion appear innocent enough. However, it has a rather chunky edge for its size and the centre is somewhat depressed.
These IIc type lesions are not commonly detected and only account for a few percent of all colorectal neoplasia. However, they are significant as, in spite of their small size, they always harbour either high-grade dysplasia or invasive cancer.
A severely disrupted or completely destroyed crypt pattern within the depressed centre, would suggest that the lesion has undergone malignant change. These lesions would be difficult to elevate at EMR due to the "desmoplastic submucosal response" associated with the invading malignant cells.
Cancers invading less than 500 µm into the submucosa will only rarely be associated with regional lymph node metastases (2-3%). However, if venous or lymphatic infiltration is found, the risks increase rapidly; 75% risk of lymph node metastases for lymphatic permeation and 40% with venous infiltration.
Lesions without lymphatic or venous permeation, invading deeper than 500 µm are also associated with an increased risk of metastases. For example carcinomas infiltrating into the middle of the submucosa (1000 µm from the muscularis mucosa) are associated with an 11% risk of metastases compared with a 15% risk for lesions invading deeper than 1000 µm.