What is a Tubular Adenoma?
A tubular adenoma is a benign neoplastic polyp of the colon and rectum characterized by glandular structures with a tubular (round, test-tube-like) architecture and dysplastic epithelium, representing the most common type of colorectal adenoma and a precursor lesion to colorectal cancer. 1
Histologic Characteristics
Tubular adenomas are composed of elongated, crowded epithelial cells forming tubular glands that resemble test tubes, with hyperchromatic nuclei that maintain polarity with respect to the basement membrane. 1
By definition, all adenomas including tubular adenomas contain some degree of dysplasia, which is classified as either low-grade (mild to moderate dysplasia) or high-grade (severe dysplasia or carcinoma in situ). 1
The neoplastic cells are elongated and crowded with hyperchromatic nuclei, distinguishing them from normal colonic epithelium. 1
Epidemiology and Distribution
Tubular adenomas represent approximately 66-83% of all neoplastic colorectal polyps, making them the most frequently encountered adenomatous polyp type. 2, 3, 4
The sigmoid colon is the most common location for tubular adenomas, followed by the descending colon. 2
These lesions can occur throughout the entire colon and rectum, though distribution varies by anatomic segment. 2
Malignant Potential
Tubular adenomas have malignant potential and are considered precursor lesions in the adenoma-carcinoma sequence, though their risk of malignant transformation is lower compared to villous or tubulovillous adenomas. 5, 6, 2
The risk of malignancy increases with larger polyp size, with invasive cancer found even in tubular adenomas less than 1 cm in diameter, though less frequently. 2, 3
Malignant transformation occurs when cancerous changes penetrate through the muscularis mucosae. 2
The presence of high-grade dysplasia in tubular adenomas significantly increases the risk of subsequent advanced neoplasia. 1
Clinical Significance and Management
All tubular adenomas should be completely removed during colonoscopy, preferably en bloc, for proper histological examination. 5, 7
Risk stratification is based on size, number, and degree of dysplasia: low-risk features include 1-2 tubular adenomas <10 mm with low-grade dysplasia and no villous components. 5, 6
High-risk features include tubular adenomas ≥10 mm, presence of high-grade dysplasia, or 3 or more adenomas. 1, 5, 6
Surveillance colonoscopy intervals range from 7-10 years for low-risk tubular adenomas to 3 years for high-risk features. 5, 6, 7