A polyp is an abnormal growth of tissue that projects from a mucous membrane, the moist lining found in various hollow organs and body cavities. These growths represent a localized overgrowth of the cells that form the inner surface of an organ. Polyps are often discovered incidentally during routine examinations or screening procedures.
What Defines a Polyp
Polyps form due to the uncontrolled proliferation of cells lining an inner surface, where the normal balance between cell growth and programmed cell death is disrupted. This cellular imbalance results in an accumulation of tissue that bulges into the open space of the organ. The epithelial lining, or mucosa, is where these growths originate.
The physical structure, or morphology, of a polyp is categorized into two main types. A pedunculated polyp grows on a thin, elongated stalk, giving it a mushroom-like appearance. Conversely, a sessile polyp has a broad base and lies flat against the surface of the underlying membrane. Sessile polyps can sometimes be more difficult to detect and remove due to their flatter profile.
Most polyps are considered benign, meaning they are non-cancerous at the time of discovery. The location and microscopic composition of a polyp are factors that ultimately determine its clinical significance.
Common Types and Locations
Polyps are characterized by their location and microscopic structure, or histology, which determines their potential for progression. Non-neoplastic polyps, such as hyperplastic or inflammatory polyps, are generally not associated with a risk of turning cancerous. Hyperplastic polyps are common, especially in the lower colon, and are typically small and harmless.
Neoplastic polyps, however, are growths that have the potential to progress to malignancy, and the most common type is the adenoma. Adenomas are categorized further as tubular, villous, or tubulovillous, based on their cellular architecture. Villous adenomas, which have a more complex structure, and polyps larger than one centimeter are typically associated with a higher degree of risk.
Colorectal Polyps
Colorectal polyps are the most common and clinically significant type, originating in the lining of the colon or rectum. The majority of these growths are adenomas, which are the precursor lesions for most colorectal cancers. The removal of adenomas is a primary goal of screening colonoscopies because of this established progression pathway. Serrated polyps, including sessile serrated lesions, are a distinct group that also carries a potential for malignant transformation.
Nasal Polyps
Nasal polyps are growths lining the nasal passages and sinuses. They are almost universally benign and are often linked to chronic inflammation, allergies, or chronic rhinosinusitis. These growths can interfere with breathing and the sense of smell, but their risk for cancer is very low.
Endometrial and Cervical Polyps
These polyps develop from the tissue lining the uterus (endometrial polyps) or on the cervix (cervical polyps). Endometrial polyps are often influenced by hormonal factors, specifically an excess of estrogen. They commonly occur in women who are perimenopausal or postmenopausal. While most are benign, there is a small potential for malignancy, and removal is often recommended, especially if they cause symptoms or appear after menopause.
Recognizing Symptoms and Diagnostic Procedures
Many polyps, particularly when small, do not cause any noticeable symptoms and are discovered only during routine screenings. When symptoms do occur, they are generally related to localized irritation, obstruction, or bleeding from the surface of the growth.
Colorectal polyps may cause bright red blood in the stool, a change in the frequency or consistency of bowel movements, or abdominal pain. Endometrial polyps often manifest as irregular uterine bleeding, such as spotting between menstrual periods or heavy flow during menstruation. Nasal polyps can lead to chronic symptoms like nasal congestion, a persistent runny nose, or a diminished sense of smell.
Diagnostic procedures are tailored to the specific area of the body being examined.
Colorectal Diagnosis
The gold standard for identifying colorectal polyps is a colonoscopy, which uses a flexible tube with a camera to visualize the entire colon. If a growth is found, the procedure allows for immediate tissue sampling or removal.
Other Locations
Endometrial polyps are often detected using a transvaginal ultrasound or a hysteroscopy, where a thin scope is inserted into the uterus. In the nasal cavity, a nasal endoscopy or a CT scan is used to visualize the polyps and assess the extent of the growth within the sinuses.
The Link to Cancer and Removal Options
The primary concern with certain types of polyps is their potential to progress to cancer over time. This progression is most clearly understood in the colon through the adenoma-carcinoma sequence, where a benign adenoma slowly transforms into a malignant tumor. Features such as a size exceeding one centimeter, the presence of villous components, or high-grade cellular abnormalities are associated with an increased risk of malignancy. Removing these growths interrupts this sequence, making polypectomy a key preventative measure.
The removal of a polyp, known as a polypectomy, is typically performed during the diagnostic procedure itself. For colorectal polyps, several techniques are used:
- Small growths may be removed using cold forceps or a cold snare, which excises the tissue without using heat.
- Larger or pedunculated polyps often require a hot snare, which uses an electric current (electrocautery) to cut the polyp and simultaneously seal the blood vessels at the base.
- Complex or very large flat polyps may require advanced techniques like Endoscopic Mucosal Resection (EMR).
Polyps in other locations are removed using location-specific methods, such as hysteroscopy and curettage for endometrial polyps. After removal, the polyp tissue is sent for microscopic examination to determine its exact type and confirm whether it contains any cancerous cells. The histological analysis dictates the need for post-procedure surveillance. The frequency of subsequent screening depends on the number, size, and type of polyps identified.