This study is designed to evaluate the diagnostic accuracy of Narrow Band Imaging (NBI) compared with High Definition White Light colonoscopy (WLE) for detection of residual neoplasia in subjects with piecemeal polypectomy scars.

Resection of large sessile polyps in the colon (usually more than 2 cm) or those nonpolypoid neoplastic lesions (also called laterally spreading tumors or LST), confers technical difficulty and often are forced to remove into fragmented resection or endoscopic piecemeal mucosal resection. This has been associated with a recurrence of 25%. For this reason, clinical guidelines recommend endoscopic follow-up at 2 to 6 months after piecemeal resection of colorectal polyps to check for residual neoplasia.

Narrow-Band Imaging (NBI, Olympus) improves visibility and identification of the surface and vascular structures of colon polyps. In contrast to conventional chromoendoscopy, it is easily activated by pressing a button on the endoscope.

Virtual or conventional chromoendoscopy are applied during resection of polyps defining the border of the lesion. However, there are few studies using Narrow Band Imaging and do not allow to know whether the use of this technique could improve the detection of residual tumor after fragmented polypectomy and avoid complications, time and costs of biopsy and histological analysis.

In this context, the European Society of Gastrointestinal Endoscopy (ESGE) has recently published the first Guideline of Advanced Endoscopic Imaging for the Detection and Differentiation of Colorectal Neoplasia and recommends conventional or virtual chromoendoscopy in patients with piecemeal polypectomy scar (strong recommendation, low quality evidence).

The investigators will perform a randomised, controlled trial of tandem colonoscopy using NBI and WLE. The main goal is to compare the rate of detected neoplasia between both techniques and evaluate the diagnostic accuracy of NBI and WLE to histology as the gold standard.

Inclusion Criteria:

• Patients over 18 years old who underwent a colonoscopy for any reason in the last 12 month
• Patients with a basal colonoscopy findings: ≥1 polyp removed in a piecemeal fashion regardless of the size

Exclusion Criteria:

• Diagnosis of a CRC in the basal colonoscopy
• Subjects who neglect to follow-up
• Subjects who do not accept informed consent
• Subjects with high risk of perforation or complications due to sedation, including patients with comorbidities (ASA IV-V)
• Inadequate bowel preparation for colonoscopy (defined by Boston Bowel Preparation Score (BBPS): ≤ 5 total points; or 0-1 points in any of the 3 segments of the colon)