Colorectal villous polyps refer to villous adenomas of the large intestine. They are most commonly found in the rectum and are the least common of all types of colon polyps.
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Epidemiology
The prevalence of advanced polyps including villous polyps on screening colonography is ~5% (range 3-7%) 3,4.
Clinical presentation
Patients with villous polyps are commonly asymptomatic but may have a range of possible signs and symptoms depending on the size, number and location of the polyps, including 3:
- hypersecretory polyps can lead to diarrhoea, fluid, protein and electrolyte disturbances (seen in McKittrick-Wheelock syndrome)
- obstructive symptoms like constipation or bowel obstruction
- acute lower gastrointestinal bleeding
- chronic bleeding causing anaemia
Pathology
Villous adenomas are an advanced form of adenoma and a precursor to cancer. Compared to tubular adenomas they are larger with 75% being over 2 cm in size and carry a higher chance of malignant transformation. Villous adenomas represent less than 5% of all adenomas. The risk of malignant transformation of the polyp increases with the presence of villous components, cellular dysplasia and the overall size 3.
Radiographic features
Fluoroscopy
On barium examinations, villous adenomas have been described as having broad bases as well as a polypoid surface that projects into the lumen with barium that travels between the clefts of the projections. When they are "carpet" lesions they may present as flat, spreading, lobulated lesions which produce subtle filling defects in the column 1.
CT and CT colonography
CT and CT colonography may reveal the following features 3:
- large lesions 2-3 cm or larger in size
- cerebriform or frondlike appearance, less commonly as "carpet" lesions which are relatively flat and lobulated in their appearance
- presence of surrounding fluid
- luminal expansion
- occasionally associated intussusception or obstruction
Evaluation of the images in both 2D and 3D formats in both the polyp and soft tissue windows is important. One view should also be obtained with the rectal balloon deflated so as to not disguise "carpet" lesions in the rectum.
In a properly prepared bowel along with CO2 distension, the detection of villous adenomas is similar to that of optical colonoscopy 2. However, undistended or unprepared bowel may only show large adenomas and cancers, with smaller lesions being more likely to be missed 3.
MRI
On MR imaging villous adenomas have the following appearances 3:
-
T1:
- low signal intensity
- vegetating shape
- polycyclic margins
- may appear less commonly as flat
-
T2:
- thick hyperintense layer along the surface of the lesion
- heterogenous intermediate to high signal intensity inside the lesion
- may have a thin central area of enhancement representing a central vascular stalk
Treatment and prognosis
Due to the risk of malignancy associated with villous adenomas the lesion is usually excised endoscopically or even surgically 3. Recurrence is a potential complication 3.
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