Serrated polyposis syndrome (SPS) is the most common colorectal polyposis syndrome and is characterized by the combination of large and/or numerous serrated lesions (SLs) throughout the colorectum. SLs are classified into sessile serrated polyps (SSP) with or without dysplasia, hyperplastic polyps (HP) and traditional serrated adenomas (TSA). In 2010 the World Health Organization (WHO) defined this syndrome by any one of the following conditions: criterion I, at least 5 SLs proximal to the sigmoid colon with 2 or more of these being >10mm in size; criterion II, any SLs proximal to the sigmoid colon in a first-degree relative with SPS; criterion III, more than 20 SLs of any size distributed throughout the colon. It has been demonstrated that 11.8-28.5% of patients with SPS present with colorectal cancer (CRC) at diagnosis. Tandem colonoscopy studies have demonstrated that a significant number of lesions are missed during conventional colonoscopy. This finding is even more evident when focusing SLs where a 31% miss rate has been reported. SLs are often overlooked due to their typical appearance: flat morphology, similar colour to the surrounding mucosa, subtle and indistinctive borders. Chromoendoscopy (dye spraying onto the surface of the colon) enhances the detection of subtle and flat polyps in the colon. Until the date no studies have assessed the use of dye-based chromoendoscopy in SPS patients.

The aim of this trial was to evaluate the usefulness of panchromoendoscopy with indigo carmine for the detection of polyps in the colon in patients with SPS. Secondary aims were to estimate the SLs and adenoma miss rates in these patients.

Patients were randomized in a 1:1 distribution to one of the two arms of the study by a list of random numbers distributed by the coordinator center. After randomization, patients were submitted to tandem colonoscopies by the same endoscopist:

• In group A (HR-WLE) the first inspection was on high-resolution white-light endoscopy from the cecum/ileo-colonic anastomosis to the rectum, followed by a second inspection also on HR-WLE.
• In group B (HR-CE) the first inspection was on HR-WLE from the cecum/ileo-colonic anastomosis to the rectum, followed by a second inspection with panchromoendoscopy. For this, the lumen was sprayed in a segmental fashion using 0.4% indigo carmine delivered via a specially designed dye spray catheter (Olympus PW-5V1) or via the accessory channel with a 50cc syringe filled with indigo carmine and air. After allowing a few seconds for the dye to settle onto the mucosal surface, excess pools of indigo carmine were suctioned and the mucosa was then scrutinised.

Time to withdrawal from the cecum was measured using a stopwatch excluding time needed for polypectomy and biopsies.

Lesions detected during each inspection were described and then removed. Size (measured in comparison with an open biopsy forceps), morphology (using the Paris classification), location and polypectomy technique were recorded before removal. Histology was used as gold standard.

Serrated polyposis syndrome (SPS) is the most common colorectal polyposis syndrome and is characterized by the combination of large and/or numerous serrated lesions (SLs) throughout the colorectum. SLs are classified into sessile serrated polyps (SSP) with or without dysplasia, hyperplastic polyps (HP) and traditional serrated adenomas (TSA). In 2010 the World Health Organization (WHO) defined this syndrome by any one of the following conditions: criterion I, at least 5 SLs proximal to the sigmoid colon with 2 or more of these being >10mm in size; criterion II, any SLs proximal to the sigmoid colon in a first-degree relative with SPS; criterion III, more than 20 SLs of any size distributed throughout the colon. It has been demonstrated that 11.8-28.5% of patients with SPS present with colorectal cancer (CRC) at diagnosis. Tandem colonoscopy studies have demonstrated that a significant number of lesions are missed during conventional colonoscopy. This finding is even more evident when focusing SLs where a 31% miss rate has been reported. SLs are often overlooked due to their typical appearance: flat morphology, similar colour to the surrounding mucosa, subtle and indistinctive borders. Chromoendoscopy (dye spraying onto the surface of the colon) enhances the detection of subtle and flat polyps in the colon. Until the date no studies have assessed the use of dye-based chromoendoscopy in SPS patients.

The aim of this trial was to evaluate the usefulness of panchromoendoscopy with indigo carmine for the detection of polyps in the colon in patients with SPS. Secondary aims were to estimate the SLs and adenoma miss rates in these patients.

Patients were randomized in a 1:1 distribution to one of the two arms of the study by a list of random numbers distributed by the coordinator center. After randomization, patients were submitted to tandem colonoscopies by the same endoscopist:

• In group A (HR-WLE) the first inspection was on high-resolution white-light endoscopy from the cecum/ileo-colonic anastomosis to the rectum, followed by a second inspection also on HR-WLE.
• In group B (HR-CE) the first inspection was on HR-WLE from the cecum/ileo-colonic anastomosis to the rectum, followed by a second inspection with panchromoendoscopy. For this, the lumen was sprayed in a segmental fashion using 0.4% indigo carmine delivered via a specially designed dye spray catheter (Olympus PW-5V1) or via the accessory channel with a 50cc syringe filled with indigo carmine and air. After allowing a few seconds for the dye to settle onto the mucosal surface, excess pools of indigo carmine were suctioned and the mucosa was then scrutinised.

Time to withdrawal from the cecum was measured using a stopwatch excluding time needed for polypectomy and biopsies.

Lesions detected during each inspection were described and then removed. Size (measured in comparison with an open biopsy forceps), morphology (using the Paris classification), location and polypectomy technique were recorded before removal. Histology was used as gold standard. Biopsies were processed and stained using standard methods, and were subsequently evaluated by experienced gastrointestinal pathologists in each center according to Vienna criteria of gastrointestinal epithelial neoplasia. Serrated lesions were classified according to the WHO 2010 classification into hyperplastic polyps, sessile serrated polyps, and traditional serrated adenomas. Cytological dysplasia among serrated polyps was analyzed both as presence/absence of dysplasia, as well as the presence of low-grade and high-grade dysplasia. Neoplastic extension vertically into the submucosal layer or beyond was classified as invasive cancer.All the procedures were done under superficial sedation (midazolam and/or fentanyl or pethidine) or under deep sedation with propofol at the discretion of the endoscopist. Procedures were performed with high definition systems [i.e: 180/190 series in combination with EVIS EXERA II-III processors (Olympus, Tokyo, Japan), EC 390 LI scope in combination with Pentax processor (Pentax, Tokyo, Japan) or 590 WL and 580 ZW endoscopes in combination with Fujinon 4400/4450 processors (Fujifilm medical systems, USA)].

Quality of bowel cleansing was graded by each endoscopist following the Boston Bowel Preparation Scale. Adequate preparation was defined as a total score ≥6 with no segments <2. Procedures in which the quality of preparation was inadequate were excluded.

Sample size calculation: a polyp miss rate of 29% with HR-WLE was described previously in a Dutch multicenter study with SPS patients. Estimating a power of 80% and a significance level of 0.05, the investigators calculated 516 lesions would be required to measure a difference of 15% on HR-CE. In a previous study a median of 6 polyps was found on annual surveillance4. The investigators calculated a simple size of 86 patients for the study, 43 on each group.

Statistical analysis was performed with SPSS version 15.0 for windows. Numeric variables are presented as mean and standard deviation in case of a normal distribution and compared with a Student´s t test. Categorical variables are presented as frequencies and compared with the Chi Square test. Polyp miss rates were compared with chi square test. Logistic regression analysis was used to compare polyp characteristics and miss rates and was expressed as Odds ratio with the confidence intervals (95% CIs) to quantify the magnitude of the associations.

Inclusion Criteria:

• Patients with Serrated Polyposis Syndrome aged 18 years or older, fulfilling WHO criteria I or III.
• Clearing of all polyps previously achieved. Polyp "clearing" considered when all polyps >3 mm were removed during previous colonoscopies and/or partial colonic surgery when needed.
• Surveillance colonoscopy.

Exclusion Criteria:

• Inflammatory bowel disease.
• Hereditary CRC syndromes (i.e, APC, MUTYH - biallelic - and MMR genes germline mutations).
• Total colectomy.
• Decline for participation.