Correlation between macroscopic morphologic features and malignant potential of colorectal sessile adenomas

To clarify malignant potential of colorectal sessile adenomas, we investigated 46 colorectal sessile adenomas surgically resected from 44 patients. Lesions were divided into three types according to their macroscopic morphologic features: nodular-type (19 adenomas), villous-type (7), and creeping-type (20). Clinicopathologic features were investigated and compared among these three types.

Frequency of focal carcinoma in the nodular-type, villous-type, and creeping-type adenoma was 37, 29, and 55 percent, respectively. Frequency of submucosal invasion in these three types were 11, 14, and 20 percent, respectively. Irrespective of the type, large lesions (> 3 cm) tended to have a higher frequency of submucosal invasion than did smaller ones (60 vs. 20 percent; P = 0.063). Large creeping-type adenomas (> 3 cm) had a definitely higher frequency of submucosal invasion than smaller ones (36 vs. 0 percent; P < 0.05). Lymphatic or vascular invasion of carcinoma was present only in the lesion with submucosal invasion: 5 percent in the nodular-type; 14 percent in the villous-type; 20 percent in the creeping-type. Lymph node metastasis was present only in the creeping-type lesion.

The large creeping-type adenomas (> 3 cm) have a definitely high frequency of submucosal invasive carcinoma. Endoscopic polypectomy or local resection may be adequate for most sessile adenomas. However, we recommend segmental resection of the colon with regional lymph node dissection for a creeping-type adenoma that is larger than 3 cm because of increased risk of submucosal carcinomatous invasion and lymph node involvement.