LearningRadiology - Colonic Polyps

Colonic Polyps

• The majority of colorectal polyps are inflammatory or metaplastic and usually 5mm or less in diameter and have no malignant potential; the majority of larger lesions are adenomatous polyps

• Predisposing conditions:

• Prior detection of colonic polyp

• Cancer of the colon

• Family history of polyps or colon cancer

• Inflammatory bowel disease (ulcerative colitis, Crohn’s)

• Familial polyposis

• Peutz-Jegher’s Syndrome

• Gardener’s syndrome

• Incidence rises with age

• About 3% in 3rd decade

• 10% in 7th decade

• 26% in 9th decade

• About 11% overall in all ages

• Most (60%) occur in rectum or sigmoid

• Types

Type

Incidence

Description

Malignant Potential

Tubular adenoma

75%

Cylindrical glandular structure lined by columnar epithelium

<10mm=1%;

1-2cm=10%; >2cm=35%

Least malignant

Tubulovillous adenoma

15%

Mixture between tubular and villous adenoma

<1cm=4%;

1-2cm=7%; >2cm=46%

Villous adenoma

10%

Infolding of papillary projections of glands

<1cm=10%;

1-2cm=10%; >2cm=53%

Most malignant

• Overall size versus malignancy: <1cm=1%; 1-2 cm=10%; >2cm= 46%

• Symptoms

• Most are asymptomatic

• Some may have diarrhea, especially villous tumors in rectum

• May also produce hypokalemia

• Abdominal pain (may be 2° to intussusception in a few)

• Rectal bleeding correlates with size and may be seen in as many as 67%

• X-ray

• Rate of detection of polyps less than 1 cm is higher with air contrast

• Rate of detection of polyps 1cm or greater is about equal with single vs. double contrast

• From 1/4 to 1/2 of patients with one polyp have a synchronous lesion

• May be sessile or on a stalk

• Bowler hat sign (sessile polyp viewed in profile on A/C exam)

• Target sign (polyp with stalk viewed en face)

• Stalk >2cm is almost always benign

• Differentiating Benign from Malignant polyps

• Size (see above)

• Presence of a stalk

• Lesions on a stalk have less of a chance of being malignant than a sessile lesion of the exact same size

• Even when malignant polyps have a stalk, the chance of spread to regional nodes is low

• Surface contour

• Not really reliable

• An ulceration is more consistent with ca

• Dimpling at the base suggests ca

• If greater than 3cm in size, barium trapped within interstices suggests villous tumor

• Location

• Does not help

• Growth

• Any polyp which undergoes an interval increase in size should be removed

Juvenile Polyps

• Classified as cystic hamatomas by some and inflammatory retention cysts by others

• No malignant potential

• Most occur as isolated colonic lesions in children less than 10 years

• Most are solitary

• Rectal bleeding is the most common symptom

• Most occur in the rectum or sigmoid

• Since they have a tendency to autoamputation, they are usually not removed

Hyperplastic Polyps

• No malignant potential

• Mucous glands lined by a single layer of columnar epithelium

• Usually located in rectum

• Usually less than 5mm in diameter