The term polyp is a misnomer, but time and universal usage have endowed it with a permanence in the field which is probably unwise and undoubtedly futile to challenge. The more precise and correct word is adenoma, and there are literally dozens of synonyms for this term. When the unmodified word polyp is used in this chapter, reference is made to the benign adenomatous variety, far and away the most common type found in man.

Countless classifications have been proposed. Some are of amazing complexity and usually constitute a plea for one or more theories of the etiology, pathology, or pathogenesis of polyps.

A simple and unpretentious classification which has the additional virtue of clinical usefulness is as follows:

1. Simple polyp

2. Villous or papillary adenoma

3. Congenital polyposis

4. Juvenile polyps

5. Pseudopolyps

Simple

Villous or papillary

Juvenile

Pseudopolyp

Fig. 67. Classification of polyps.

Simple polyp (Fig. 67). This is by far the most common type, being detectable sigmoidoscopically in from about 2 to 10% of adults, depending on age and sex. Such polyps are more common in males than in females, and the incidence increases with advancing years.

The most important facts to know about the pathology of simple polyps are as follows:

1. Usually single but may be multiple

2. May be sessile or pedunculated

3. Color ranges from pink to deep red

4. Size ranges from a few millimeters to several centimeters (majority less than 2 cm.)

5. May arise from an area of mucosal hyperplasia

6. Have great significance as a premalignant lesion (see below)

7. May actually be malignant when first seen

Villous or papillary adenoma (Fig. 67). Some feel that the villous or papillary adenoma is merely a variant of the simple polyp. However, it appears to have enough distinctive features to warrant its separation from the benign adenomatous variety:

1. Most often single

2. Less than 15% of all polyps are of this type

3. Usually sessile and soft

4. Characterized by presence of innumerable soft, branching villi or projections on surface

5. May be vascular and may secrete large amounts of mucus

6. Usually located in the rectum

7. Occasionally prolapse

8. 20 to 30% are malignant when first seen

9. Marked tendency for recurrence after local removal, even when benign 10. High incidence of subsequent carcinoma in or at site of these lesions Congenital polyposis. It is possible that this is merely an extreme variety of multiple simple polyps, but its clear-cut familial background plus the widespread distribution of an enormous number of lesions serve to set it apart for separate consideration. Its chief features are as follows:

1. Definite hereditary setting, transmitted genetically as dominant by males and females to offspring of both sexes.

2. Usually diagnosed in second to fourth decade of life (most often when patient is in his 20's)

3. Bowel may be studded from cecum to anus with innumerable polypoid lesions

4. At time of diagnosis the majority (possibly 50 to 80%) of patients will have cancer in one or more polyps

5. Generally conceded that 100% of these individuals will develop cancer if lesions left in place

Juvenile polyp (Fig. 67). Juvenile polyps also are called cystic or retention polyps. Their main features are as follows:

1. Most commonly occur in first decade of life

2. Usually single

3. Honeycomb or lattice-work appearance on gross section

4. Evidence of retention cysts containing mucin on microscopic examination

5. Tendency to recurrence not noted

6. No precancerous significance or potential

Pseudopolyp (Fig. 67). Pseudopolyps are not true adenomas at all but are included because the distinction of one from the other may be difficult clinically. Their main distinguishing characteristics are as follows:

1. Usually result from inflammatory disease of bowel, most notably ulcerative colitis.

2. Number and distribution depend on extent and type of preceding inflammation but may be widespread and multiple.

3. Not premalignant in themselves but the bowel which harbors them may have a very high cancer potential.