A polyp in the colon is a small cluster of cells that grows on the lining of the large intestine. These growths are extremely common, affecting a significant portion of the adult population, and are typically discovered during a colonoscopy. Polyps are categorized based on their appearance and the risk they carry for developing into cancer. Hyperplastic polyps are a specific and frequently encountered type of colonic growth. Understanding their nature is important because their presence affects future surveillance planning.
What Defines a Hyperplastic Polyp
The term “hyperplastic” refers to an overgrowth of normal, mature epithelial cells lining the colon. These polyps are classified as non-neoplastic, meaning they do not follow the standard pathway to malignancy, unlike truly precancerous polyps. They are typically sessile, or flat, and are usually quite small, measuring less than five millimeters in diameter.
They are most commonly found in the distal colon, specifically the sigmoid colon and the rectum. Microscopically, the cells show features of a mature cell line, including small, regular nuclei positioned near the base of the cell. The crypts, which are the small glands of the colon lining, appear elongated and have a distinctive serrated or sawtooth-like pattern in the upper portion. The cell division is strictly limited to the base of the crypts, confirming benign cellular behavior.
The Different Subtypes of Hyperplastic Polyps
Pathologists recognize two main histological subtypes of hyperplastic polyps based on their cellular composition and structure.
Microvesicular Mucin-Rich Type
This type is characterized by abundant, small mucin droplets within the surface epithelial cells, giving the cell cytoplasm a glassy or hazy appearance. This subtype is frequently associated with the BRAF gene mutation. The serration pattern is typically prominent toward the luminal surface of the polyp.
Goblet Cell-Rich Type
This classification features elongated crypts filled with prominent, mature goblet cells extending toward the surface. This subtype often shows less pronounced serration and can sometimes be associated with a KRAS gene mutation.
Although these two subtypes have distinct molecular and microscopic signatures, the clinical implication is generally the same. Both microvesicular and goblet cell-rich hyperplastic polyps carry a very low risk of developing into cancer when found in isolation.
Distinguishing Hyperplastic Polyps from Precancerous Lesions
Hyperplastic polyps belong to the larger family of “serrated polyps.” This classification can cause confusion because the group also contains lesions with malignant potential. The distinction between a benign hyperplastic polyp and a precancerous sessile serrated lesion (SSL) is important. SSLs are recognized precursors to colorectal cancer and are considered high-risk lesions that arise via a different molecular pathway than traditional adenomas.
Endoscopically, hyperplastic polyps tend to be small, pale, smooth, and flat, most often located in the lower left side of the colon. In contrast, SSLs are typically larger, often exceeding five millimeters, and favor the proximal, or right side, of the colon. SSLs can be subtle and challenging to detect due to their flat, low-profile growth pattern and indistinct borders.
A visual differentiator for a precancerous SSL is the frequent presence of a “mucus cap,” a thin layer of mucus adhering to the surface. While hyperplastic polyps are smooth, SSLs may exhibit a cloud-like or granular surface. Microscopically, SSLs show serration that extends all the way to the base of the crypt, along with characteristic crypt dilation or a distinct boot-shape. This feature is absent in hyperplastic polyps. This microscopic confirmation is why every removed polyp must be examined by a pathologist to accurately determine the risk.
Management and Follow-up After Diagnosis
Management of a hyperplastic polyp begins with its removal during the colonoscopy procedure. Removal is necessary because it is impossible to distinguish it from a precancerous lesion by sight alone. Once the pathology report confirms the lesion is a small hyperplastic polyp, particularly one located in the distal colon, the patient is considered low-risk.
For those with one or a few small hyperplastic polyps, standard surveillance guidelines recommend returning to a routine screening interval, typically ten years after the initial procedure. This long interval reflects the extremely low malignant potential of these specific polyps.
The surveillance schedule changes significantly if the pathologist identifies other types of polyps, such as SSLs or traditional adenomas. Finding a larger hyperplastic polyp (10 millimeters or more) or multiple polyps also suggests a need for a shorter follow-up interval, typically three to five years, to monitor for higher-risk lesions.