Introduction

Colonoscopy is a vital diagnostic and screening tool used to examine the inner lining of the colon and rectum. This procedure plays a crucial role in detecting and preventing colorectal diseases, particularly colorectal cancer.^1,2

Colorectal cancer is one of the leading causes of cancer-related deaths worldwide, often developing from precancerous polyps known as adenomas. Among these, tubular adenomas are the most common type of adenomatous polyps. While they are generally benign, they can potentially progress into malignant tumours over time if left untreated.²

The significance of colonoscopy in early detection lies in its ability to identify and remove these precancerous lesions before they transform into cancer. Regular colonoscopy screenings reduce the incidence and mortality of colorectal cancer by detecting and removing adenomas at an early stage. With advancements in colonoscopic technology, including high-definition imaging and artificial intelligence (AI)-assisted detection, the accuracy and efficiency of detecting tubular adenomas have significantly improved.³

Understanding tubular adenomas

Definition 

Tubular adenomas are a type of adenomatous polyps found in the colon and rectum. These polyps arise from glandular cells in the mucosal lining of the colon and have a characteristic tubular architecture when examined under a microscope. They are classified as neoplastic lesions (abnormal growths or masses), meaning they have the potential to develop into cancer over time.^2,4

Classification and characteristics

Tubular adenomas vary in size and appearance. They are generally classified based on:^3,5

• Size: Small (<10 mm), medium (10–19 mm), or large (≥20 mm). The risk of malignancy increases with size
• Dysplasia: Tubular adenomas show varying degrees of dysplasia (abnormal cellular growth), ranging from low-grade (mild abnormalities) to high-grade (severe abnormalities with a higher risk of progression to cancer)
• Growth pattern: They typically exhibit a smooth, pedunculated (stalked), or sessile (flat) shape

Tubular adenomas are distinct from villous and tubulovillous adenomas, which contain more villous structures and have a higher risk of malignancy. Among all adenomatous polyps, tubular adenomas have the lowest malignant potential, however, they are the most commonly detected type.⁵

Progression to colorectal cancer

The adenoma-carcinoma sequence is a well-documented process describing how benign adenomas can evolve into colorectal cancer; this progression occurs due to accumulated genetic mutations, including alterations in the APC gene, KRAS mutations, and loss of p53 function. The likelihood of malignant transformation depends on several factors:^3,5,6

• Adenomas of sizes greater than 10 mms are more likely to develop high-grade dysplasia or carcinoma
• High-grade dysplasia indicates a more advanced precancerous stage
• Sessile growth patterns and flat polyps are harder to detect and could pose a higher risk

Since most colorectal cancers develop from adenomas, early detection and removal of tubular adenomas through colonoscopy is crucial. Identifying these polyps before they progress to cancer significantly reduces the risk of colorectal cancer and improves patient outcomes. Regular screening, particularly in high-risk individuals, plays a key role in preventing colorectal malignancies.⁶

Colonoscopy as a diagnostic tool

Mechanism and procedure of colonoscopy

Colonoscopy is a minimally invasive endoscopic procedure used to examine the colon and rectum for abnormalities, including polyps, inflammation, and cancer. It involves inserting a colonoscope, a flexible tube with a light and high-resolution camera, through the rectum to visualise the inner lining of the colon. The procedure typically requires bowel preparation, where patients take a laxative solution to clear the intestines for optimal visibility.^6,7

During the procedure, the endoscopist carefully inspects the colon and could perform:^6,7

• Biopsy: A small tissue sample is taken for histological examination
• Polypectomy: Removal of polyps, including tubular adenomas, using a snare or electrocautery

The entire process usually takes 20 to 45 minutes, and patients can receive sedation for comfort.⁷

Effectiveness in detecting adenomas

Colonoscopy is the gold standard for detecting colorectal polyps, including tubular adenomas. The effectiveness of colonoscopy is often measured by the adenoma detection rate (ADR), which reflects the percentage of screened patients in whom at least one adenoma is found. A higher ADR correlates with a lower risk of developing colorectal cancer. Despite its effectiveness, some polyps, especially flat or sessile lesions, can be missed, which can lead to interval colorectal cancers (cancers developing between screenings).^8,9

Advancements in colonoscopic technology

Recent innovations have improved the accuracy of adenoma detection:

• High-definition colonoscopy provides clearer images for better polyp visualisation
• Chromoendoscopy uses special dyes (e.g., indigo carmine, methylene blue) to enhance mucosal details
• Narrow band imaging (NBI) improves contrast and highlights abnormal tissue
• Artificial intelligence (AI)-assisted detection utilises AI-powered software to help identify subtle adenomas in real time, increasing diagnostic accuracy¹⁰

By combining traditional colonoscopy with these advancements, the detection rate of tubular adenomas has significantly improved, leading to better prevention of colorectal cancer through early intervention.

Benefits of early detection of tubular adenomas

Prevention of colorectal cancer (CRC)

The primary benefit of detecting tubular adenomas early is the prevention of colorectal cancer (CRC). Since most CRCs develop through the adenoma-carcinoma sequence, identifying and removing these precancerous polyps during a colonoscopy reduces the likelihood of malignant transformation. 

Reduction in colorectal cancer mortality

Early detection and removal of adenomas before they progress into high-grade dysplasia or invasive cancer leads to a lower mortality rate from CRC. When it is diagnosed at an early, localised stage, the 5-year survival rate exceeds 90%, compared to a much lower survival rate for advanced-stage cancers.¹¹

Less invasive and cost-effective treatment

Detecting and removing small tubular adenomas during a colonoscopy is a minimally invasive and cost-effective procedure. In contrast, treating advanced colorectal cancer could require:

• Surgery (colectomy)
• Chemotherapy or radiotherapy
• Long-term monitoring and follow-up care

Early polypectomy reduces the need for these complex and expensive interventions, lowering the overall healthcare burden.¹²

Improved public awareness and screening compliance

Promoting colonoscopy screening programs increases public awareness about the importance of early detection. Countries with organised screening programs, such as the U.S. and European nations, have observed a significant decline in CRC incidence and mortality over the years. Encouraging high-risk individuals, for example, those with a family history of CRC, to undergo routine colonoscopies helps in early intervention and disease prevention.¹³

Summary

Colonoscopy remains the gold standard for detecting and preventing colorectal cancer by identifying and removing tubular adenomas before they progress into malignancy. Since colorectal cancer follows the adenoma-carcinoma sequence, early detection through colonoscopy significantly lowers cancer incidence and improves survival rates. The integration of high-definition imaging, artificial intelligence (AI), and advanced endoscopic techniques has enhanced the accuracy of adenoma detection, reducing the risk of missed lesions. Regular colonoscopic screening plays a crucial role in colorectal cancer prevention, and its widespread implementation could lead to significant reductions in mortality and healthcare costs. Encouraging individuals, particularly those at higher risk, to undergo routine screenings is essential for improving public health outcomes.