Polyps are abnormal tissue growths that can form on the lining of various organs. While many types exist, a specific kind, known as a flat polyp, distinguishes itself through its unique morphology. These flat growths present a particular challenge in medical examination due to their subtle nature.
Defining Flat Polyps
Flat polyps possess a distinctive appearance, lying nearly flush with the surrounding tissue or exhibiting only a slight elevation. This characteristic sets them apart from more commonly recognized polyp shapes. In contrast, pedunculated polyps resemble mushrooms, connected to the organ lining by a thin stalk, while sessile polyps are broad-based but still visibly raised. Flat polyps, sometimes referred to as sessile serrated lesions or sessile serrated adenomas, grow by spreading laterally along the organ wall rather than growing outward.
These polyps can develop in various parts of the gastrointestinal tract, though they are frequently encountered in the colon. Flat polyps represent the least common type of colon polyp, accounting for approximately 2% to 10% of discovered lesions.
The Significance of Flat Polyps
Flat polyps present a particular concern in medical practice due to their potential to develop into advanced precancerous lesions or even cancer, specifically adenocarcinoma. Despite their subtle, flat appearance, these polyps can harbor aggressive cellular changes.
A significant challenge associated with flat polyps is their difficulty in detection during routine screenings. Their subtle morphology, which allows them to blend in with the surrounding tissue, makes them easily missed during visual inspection. This subtle nature can render them more problematic than other types of polyps, as a missed flat polyp may contribute to the development of interval cancers, which are cancers detected between scheduled screenings.
Identification and Removal
Colonoscopy remains the primary method for identifying flat polyps. During this procedure, healthcare providers employ various advanced techniques to enhance visibility and improve detection rates. Chromoendoscopy, for instance, involves spraying dyes onto the mucosal surface to highlight architectural details, making flat and depressed lesions more discernible. Narrow-band imaging (NBI) is another technique that modifies white light into specific wavelengths absorbed by hemoglobin, thereby enhancing the visualization of vessels and surface patterns of lesions.
Once identified, flat polyps are typically removed using endoscopic techniques. Polypectomy is the general term for polyp removal, but for flat polyps, specialized methods are often necessary. Endoscopic mucosal resection (EMR) is a common technique where a solution, often saline, is injected beneath the polyp to lift it from the deeper muscle layers, creating a cushion that facilitates safe removal with a snare. This method is particularly suitable for large and flat lesions, and it helps to avoid the need for more invasive surgery.
For larger or more complex flat polyps, endoscopic submucosal dissection (ESD) may be employed. ESD involves injecting fluid into the submucosa and then using specialized knives to precisely dissect the lesion from the underlying layers, allowing for en bloc (in one piece) removal. While more technically demanding and potentially associated with a higher perforation rate than EMR, ESD offers the advantage of complete, single-piece removal, which is important for accurate pathological evaluation and reducing recurrence. Following removal, follow-up surveillance is important to monitor for any recurrence based on the polyp’s characteristics.