Gastrointestinal Imaging

Familial adenomatous polyposis

(also called familial multiple polyposis), hereditary disorder with dominant autosomal inheritance, characterized by the presence of multiple (more than a hundred) adenomatous colorectal polyps and the inevitable development of carcinoma. Familial adenomatous polyposis (FAP) is part of the adenomatous polyposis syndromes including the Gardners syndrome and Turcots syndrome and an attenuated form of FAP. The disorder is due to a severe mutation in the APC gene with a high penetrance (80 100%). Two-thirds of the affected individuals have a familial history of polyposis.

The polyps can involve the whole colon but with a predilection for the left colon. Their size is variable: from pin point to more than 1 cm or larger. Most are sessile but they may also be pedunculated. They present in two patterns: in the first instance, called the "carpet pattern" instance, innumerable very tiny polyps cover the entire surface of the mucosa; in the second fewer, unevenly distributed and somewhat larger polyps are observed. From a histopathological point of view the polyps have a tubular structure which is similar to the common sporadic adenomas. In the larger polyps a villous or a tubular-villous composition is seen. Although these lesions develop during the first and second decade, clinical symptoms will be present only at a later age, mostly during the third and fourth decade and they are frequently related to the development of carcinoma. Clinical symptomatology consists of abdominal pain, blood loss, diarrhoea with electrolyte depletion and weight loss.

Double contrast barium study plays a major role in displaying the exact extent and distribution of the colon polyps. In accordance with the above mentioned gross morphology classification, radiological examination will reveal either innumerable small filling defects carpeting the whole colon mucosal surface (Fig.1) or more widely scattered, larger filling defects as seen in the common adenomas of the colon. If carcinoma has developed it will generally display the same features as the common carcinoma and may appear as polypoid or infiltrating and stenosing lesions. Double contrast barium enema is also a major tool in the preventive screening of individuals for earlier detection of FAP.

It is assumed that polyp formation may be present in the stomach in 30100% of patients with FAP. In most instances non-neoplastic fundus polyps are seen. These fundic gland polyps are usually not associated with chronic non specific gastritis nor with an increased risk of carcinoma. Polyps in the antrum of the stomach in patients with FAP are of the adenomatous type. In FAP patients adenomatous polyps occur with increased frequency in the duodenum, particularly in the peripapillary region. According to reports jejunal polyps occur in 40% and ileal polyps in 20% of FAP patients, although malignant degeneration seems to be unusual. Finally, it is reported that adenomatous polyps occur with increased frequency in the distal ileum of patients with FAP treated with total colectomy.

ALB

Fig.1

Barium enema. Innumerable, round, tiny filling defects are visible in the transverse and descending colon, as well as in the sigmoid colon.

Familial adenomatous polyposis, Fig.1