Hereditary Mixed Polyposis Syndrome
Differential Diagnosis
The gastrointestinal polyps in some cases are indistinguishable
| Hereditary Mixed Polyposis |
Familial Adenomatous Polyposis |
| Mixtures of adenomatous and juvenile type polyps |
Colorectal polyps are all adenomatous |
| Polyps may have mixed adenomatous and juvenile features |
Colorectal polyps lack juvenile features |
| No extra-colorectal associated lesions |
May be associated with duodenal adenomas, gastric fundic gland polyps, desmoid tumors and other extra-gi disorders |
| No APC mutation |
Mutation in APC gene |
| Cowden Disease |
Hereditary Mixed Polyposis Syndrome |
| Most cases present in childhood |
Mean age at presentation 41 years |
| Usually 50-200 polyps |
Usually 1-15 polyps, rarely >50 |
| Adenomas infrequent |
Adenomas common |
| Most have facial mucocutaneous lesions, see description |
No associated mucocutaneous lesions |
| Frequent breast hamartomas and carcinomas |
No association with breast hamartomas or carcinomas |
| Frequent thyroid carcinomas |
No association with thyroid carcinomas |
The polyps in some cases are indistinguishable
The polyps in some cases are indistinguishable
| Serrated Polyposis (Hyperplastic Polyposis) |
Hereditary Mixed Polyposis |
| Adenomatous cytologic features infrequent, focal at most |
Most polyps are adenomatous, either pure or mixed |
| Most polyps are sessile |
Most are polypoid, regardless of histology |
| Glands are vertically arranged and not complex |
Frequently shows features of juvenile polyps: prominent stroma, cystic dilation |
