Sessile serrated adenomas (SSAs) are a specific type of growth found in the colon. These growths are recognized as precursor lesions, meaning they have the potential to develop into colorectal cancer if left undetected and untreated.
What Makes Sessile Serrated Adenomas Unique?
Sessile serrated adenomas are distinct from other common polyps in their appearance and microscopic characteristics. The term “sessile” indicates that the polyp is flat or broad-based, growing directly against the colon wall without a stalk. This flat morphology can make them challenging to identify during endoscopic procedures.
Microscopically, SSAs are characterized by a “serrated” or saw-toothed appearance of the glandular structures. Unlike conventional adenomas, SSAs typically do not show the same nuclear changes. Instead, their unique features include dilated crypt bases, crypts that can grow horizontally, and abnormal branching patterns, sometimes described as L-shaped or boot-shaped glands. SSAs are frequently found in the right side of the colon.
Why Understanding SSA is Crucial
Sessile serrated adenomas are significant because they are considered precancerous lesions, capable of progressing into colorectal cancer. This progression occurs through a distinct molecular pathway known as the “serrated pathway,” which differs from the more commonly understood adenoma-carcinoma sequence. Approximately 15% to 30% of colorectal cancers are believed to originate from this pathway.
SSAs are also implicated in the development of “interval cancers,” which are cancers detected between recommended screening colonoscopies. This occurs because their subtle, flat nature makes them difficult to detect. Moreover, SSAs often do not cause any noticeable symptoms, underscoring the importance of regular colorectal cancer screening.
How SSAs Are Discovered
Sessile serrated adenomas are primarily identified during routine colonoscopies, a procedure where a flexible tube with a camera examines the inner lining of the colon. Detecting SSAs presents unique challenges due to their flat, subtle appearance, often blending with the surrounding mucosa, and sometimes being covered by a mucus cap.
Once a suspicious lesion is identified, a biopsy is taken for pathological examination. The definitive diagnosis of an SSA relies on microscopic analysis by a pathologist, who looks for specific architectural features to confirm its presence.
Next Steps After an SSA Diagnosis
The standard management for a sessile serrated adenoma is complete endoscopic removal, typically performed during a colonoscopy. This procedure, known as polypectomy, aims to eliminate the lesion entirely.
Due to their flat shape and indistinct borders, SSAs can be challenging to remove completely, leading to a higher risk of incomplete resection compared to other polyp types. Following removal, specific surveillance guidelines are recommended, often involving more frequent follow-up colonoscopies than for some other types of polyps.
For instance, intervals may range from 3 to 5 years for smaller SSAs without dysplasia, but can be as frequent as 1 year for larger lesions or those showing signs of dysplasia. Adherence to these schedules is important for preventing the potential development of colorectal cancer.