A polyp is an abnormal growth of tissue projecting from a mucous membrane and maybe pedunculated (with a stalk) or sessile (flat). Polyp is a morphological description. Polyps in the colon and rectum are most frequently adenomas histologically.
Pedunculated polyp in sigmoid colon:
Sessile polyp in caecum:
Most are asymptomatic and found on investigation for symptoms caused by other pathology or at bowel cancer screening (cause occult bleeding picked up by Haemoccult test- see podcast on screening). Can cause pr bleeding (small amounts) if in the rectum or left colon and occasionally increased awareness of flatus (flatus builds up behind larger polyps to be released more obviously in one go!) or loose stool as the polyps get larger.
They are common and increase with age, especially over 50 years.
Polyps can be removed at colonoscopy using a diathermy snare passed down the scope. Large polyps may need to be removed surgically with the part the of the bowel in which they lie.
Snaring of pedunculated polyp:
Histologically into :
A. neoplastic (which can be benign or malignant)
A.Benign Neoplastic Polyps (Adenomas)
Arise from the glandular epithelium of the large bowel. As such they are ADENOMAS.
Benign neoplasms but considered to be precursor to colorectal cancer (see adenoma-carcinoma sequence).
Histologically divided into tubular, villous and tubulovillous.
Rare neoplastic polyps include lymphoma, lipoma and haemangioma.
Convincing circumstantial evidence but no conclusive evidence.
Both conditions more prevalent in western societies in which diet is low in fibre and high in red meat.
Similar topographic distribution of adenomas and carcinomas in the GI tract.
Synchronous existence of adenomas and carcinomas.
Adenomas > 1cm exhibit signs of dysplasia and malignant transformation. Vice versa, histological studies of carcinomas reveal adenomatous elements within tumour. Thought to be about a 10% chance of a 1cm adenoma becoming a cancer within 10 years.
Average age of patients with adenoma is 7-8 years younger than patients with carcinomas.
Removing polyps endoscopically has been shown to decrease the incidence of colorectal cancer.
Familial Adenomatous Polyposis (FAP) where hundreds of adenomatous polyps are seen, all patients eventually develop cancer by the age of 40.
Usually small and incidental findings.
Hamartoma - a benign focal malformation composed of tissue elements normally found at that site, but which are growing in a disorganized mass at the same rate as the surrounding tissues.
Hyperplastic polyp - Increase in the number of cells leading to enlargement of the tissue (and formation of a polyp). Histologically looks the same as normal cells. these too can lead to malignancy via a hyperplastic polyp - serrated adenoma - adenocarcinoma pathway. Increased risk in patients with acromegaly. (NB hyperplasia increased number of normal cells, hypertrophy increased size of normal cells).
MALIGNANT POLYPS - EARLY ADENOCARCINOMAS (pT1)
The diagnosis of malignant change within an adenoma (adenocarcinoma) requires invasion of neoplastic cells through muscularis mucosa into the submucosa. Hence, malignant cells limited to the mucosa should be described as high grade dysplasia rather than intramucosal carcinoma.
5% of colonoscopically removed polyps, increases with polyp size.
Staging of pedunculated polyps- Haggitt Levels
The red colour indicates level of cancer within polyp. The chance of lymph node metastasis increases with Haggitt level.
Dr Haggitt was an American Pathologist at the University of Washington who developed the above staging system. He was shot dead in his office by one of his trainees in 2000.
Staging of sessile polyps-Kikuchi Levels
The frequency of lymph node metastasis in sessile tumours correlates to the depth of invasion of the submucosa (i.e, sm1: 2%, sm2: 8% and sm3: 23%).
It should be noted that both staging systems have advantages and disadvantages and can be problematic to use in practice, particularly if there is fragmentation or not accurate orientation of the tissue following polypectomy. More recently, new staging systems have been introduced that involve measuring the depth of invasion in microns from the muscularis mucosa into the submucosa.
Management of malignant adenomas
Controversial but should be based on histological staging. The risk of death from surgery should be less than the risk of death from spread of the cancer.
Haggitt level 1 malignant adenomas can probably be treated by polypectomy alone.
The presence of lymphatic invasion, neoplastic cells at the resection margin and poorly differentiated carcinomas within an adenoma necessitate surgical resection.
Sessile malignant adenomas also mostly require surgical resection particularly since depth of invasion increases risk of lymph node involvement.
There are several syndromes associated with multiple colonic polyps and include:
Familial adenomatous polyposis
Juvenile polyposis syndrome
The New Aird's companion in surgical studies. 3rd Edition, 2005.
Classification of colorectal cancer based on correlation of clinical, morphological and molecular features
Colorectal cancer: genetics of development and metastasis
Surveillance guidelines after removal of colorectal adenomatous polyps - British Society of Gastroenterology