Hereditary polyposis syndromes are inherited conditions characterized by development of numerous polyps in the colon and rectum. The most common form is familial adenomatous polyposis (FAP — APC gene mutation, autosomal dominant) with 100-1000+ adenomatous polyps. Carries 100% cancer risk if untreated. Other forms: attenuated FAP (AFAP, 10-100 polyps), MUTYH-associated polyposis (MAP, autosomal recessive), Peutz-Jeghers syndrome (hamartomatous polyps), juvenile polyposis, and Cowden syndrome.
Age Range
10-40
Peak Age
25
Gender
Equal
Prevalence
Rare
FAP has a germline mutation in the APC (adenomatous polyposis coli) tumor suppressor gene (chromosome 5q21). APC protein regulates beta-catenin degradation — mutation leads to beta-catenin accumulation constitutively activating the Wnt signaling pathway, causing uncontrolled cell proliferation. Since every colonic epithelial cell already carries one mutant APC allele, loss of the second allele (LOH — loss of heterozygosity) occurs easily and numerous independent adenomas develop. This perfectly exemplifies the 'two-hit' hypothesis. Polyps begin in adolescence and become widespread by the 20s. Cancer develops at an average age of 39 without treatment. Gardner syndrome is a variant of FAP with extra-colonic findings (desmoid tumor, osteoma, epidermoid cyst). CT colonography shows hundreds of polyps throughout the colon — 'carpet of polyps' appearance is characteristic.
More than 100 adenomatous polyps throughout the colon on CT colonography — 'carpet of polyps' appearance completely covering the mucosal surface. This finding is the signature of familial adenomatous polyposis and confirms genetic testing indication.
Hundreds to thousands of polypoid lesions throughout the colon — 'carpet of polyps' appearance. Mucosal surface irregular and lobulated. Polyps of varying sizes (few mm to >20 mm).
Report Sentence
Innumerable polypoid lesions are seen throughout the colon with a 'carpet of polyps' appearance, consistent with familial adenomatous polyposis.
Abdominal desmoid tumor in Gardner syndrome — low to moderate density, slowly enhancing mass in mesentery or abdominal wall. Develops in 10-20% of FAP patients. Frequency increases after surgery.
Report Sentence
A soft tissue mass measuring approximately ___ cm consistent with desmoid tumor is seen in the mesentery/abdominal wall.
Multiple polyps in the duodenum, especially periampullary region. Duodenal polyps develop in 80-90% of FAP patients. Ampullary adenomas increase pancreaticobiliary carcinoma risk.
Report Sentence
Multiple polypoid lesions are seen in the duodenum, consistent with duodenal adenomas in the setting of FAP.
Osteomas in mandible or maxilla in Gardner syndrome — dense sclerotic bone lesions on CT. Dental anomalies (supernumerary teeth, odontomas) may accompany.
Report Sentence
A sclerotic osteoma is seen in the mandible and should be evaluated in the context of Gardner syndrome.
Focal mass/wall thickening on polyposis background — suggests malignant transformation focus. Asymmetric thickening, luminal narrowing, pericolic fat stranding, and lymphadenopathy increase suspicion.
Report Sentence
A focal mass formation in the ___ segment on a polyposis background is seen and should be evaluated for malignant transformation.
Mesenteric desmoid tumor shows variable signal on T2W MRI — hyperintense in active/cellular phase, hypointense in mature/fibrotic phase. Intermediate-low signal on T1W.
Report Sentence
T2W signal in the mesenteric desmoid tumor is evaluated as ___ and should be compared with prior study for disease activity.
Criteria
APC mutation, >100 adenomatous polyps. Usually begins in adolescence.
Distinct Features
100% cancer risk without treatment. Prophylactic colectomy recommended in 20s. Extra-colonic screening mandatory.
Criteria
APC mutation (5' or 3' end), 10-100 polyps. Late onset, right colon predominance.
Distinct Features
Cancer risk 70% (lifetime). Close colonoscopic follow-up or colectomy. Distinguished from sporadic multiple polyps by genetic testing.
Criteria
FAP + extra-colonic findings: desmoid tumors, osteomas, epidermoid cysts, supernumerary teeth.
Distinct Features
Desmoid tumors may be the main cause of morbidity and mortality. Mesenteric desmoid frequently develops post-surgery. Abdominal CT follow-up critical.
Distinguishing Feature
Sporadic adenomatous polyps are usually <3 and focal. FAP shows >100 polyps with widespread distribution throughout colon. Genetic testing is definitive differentiator.
Distinguishing Feature
Pseudopolyps (inflammatory) may be seen in ulcerative colitis but are not true adenomatous polyps. Continuous mucosal inflammation, wall thickening, and haustral loss are characteristic. FAP has true adenomatous polyps.
Distinguishing Feature
Lymphomatous polyposis (mantle cell lymphoma) may show multiple polypoid lesions but accompanied by homogeneous low enhancement, lymphadenopathy, and splenomegaly. FAP has true adenomatous histology and APC mutation is diagnostic.
Distinguishing Feature
Adenocarcinoma may develop on FAP background but shows focal mass/invasion findings. Asymmetric thickening and pericolic invasion on polyposis background suggests malignant transformation.
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
6-monthFAP diagnosis confirmed by genetic testing (APC mutation). Prophylactic colectomy is mandatory to prevent cancer development — total colectomy + ileal pouch-anal anastomosis (IPAA) or total proctocolectomy + permanent ileostomy options available. Surgical timing: age 20-25 if asymptomatic, earlier if dysplasia present. Post-colectomy follow-up: upper GI endoscopy (duodenal polyps) every 1-3 years, thyroid US annually, desmoid screening (abdominal CT/MR) every 1-3 years. Genetic counseling and APC testing mandatory for first-degree relatives. Close colonoscopic follow-up (annual) may be alternative in AFAP.
Prophylactic colectomy (typically in 20s) is life-saving. Family screening is done with APC gene testing. Gardner syndrome (desmoid, osteoma, epidermoid cyst) and Turcot syndrome (brain tumors) may accompany.