Familial Adenomatous Polyposis

Familial adenomatous polyposis is an autosomal dominant colorectal polyposis syndrome caused by a pathogenic APC variant.

Classic disease produces hundreds to thousands of colorectal adenomas, usually beginning during adolescence. Untreated classic disease carries an almost inevitable lifetime colorectal cancer risk.

Extracolonic disease includes duodenal and ampullary adenomas, desmoid tumours, thyroid cancer and other APC associated manifestations.

Most affected adolescents are asymptomatic despite a large polyp burden.

Later manifestations include rectal bleeding, anaemia, altered bowel habit or cancer related symptoms.

Family history is important, but a pathogenic APC variant may arise de novo.

Confirm the diagnosis with genetic testing where possible.

Begin lower gastrointestinal surveillance during adolescence. Classic FAP generally requires colonoscopy every 1 to 2 years beginning around age 10 to 15 years.

Upper gastrointestinal surveillance with visualisation of the ampulla should begin approximately age 20 to 25 years, with subsequent intervals determined by duodenal disease burden.

Colectomy prevents colorectal cancer but timing and reconstruction depend on polyp burden, rectal disease, genotype, symptoms and ability to maintain lifelong surveillance.

Absolute indications for surgery include:

• Colorectal cancer or strong suspicion of cancer
• Significant bleeding or obstruction
• Polyp burden that cannot be controlled endoscopically
• Advanced dysplasia or other high risk pathology.

Ileorectal anastomosis

Total colectomy with ileorectal anastomosis is suitable when rectal disease is limited and can be controlled endoscopically.

It provides better bowel function and avoids pelvic pouch surgery, but the retained rectum remains at lifelong cancer risk and requires frequent surveillance.

Ileal pouch anal anastomosis

Total proctocolectomy with ileal pouch anal anastomosis is preferred with substantial rectal polyposis, rectal cancer, advanced rectal neoplasia or inability to maintain reliable rectal surveillance.

A rectal polyp burden above approximately 20 adenomas is commonly used as one factor favouring pouch surgery.

Total proctocolectomy with end ileostomy is reserved for patients in whom pouch construction is unsuitable or undesirable.

Neither colectomy nor pouch surgery ends surveillance. Residual rectal, pouch, cuff and duodenal mucosa remain at risk for neoplasia.

Desmoid risk should be considered before repeated abdominal operations, particularly in patients with strong family or genotype related risk.