Multiple Colorectal Adenomas Syndrome with Malignant Degeneration in Multiple Colorectal Polyps: ¹⁸F-Fluorodeoxyglucose Positron Emission Tomography–Computed Tomography Findings

A 61-year-old male presented with 3 months history of episodes of bleeding per rectum. A colonoscopy was performed which revealed ulcerative lesion at anorectal junction. Also noted were multiple sessile and pedunculated polyps in the entire colon, but none were ulcerated or obstructive. A biopsy was performed from the anorectal lesion which showed Grade 2 adenocarcinoma. Biopsy from one other sigmoid colon polyp was negative for malignancy. Hence, a diagnosis of polyposis coli with anorectal adenocarcinoma was made. Serum carcinoembryonic antigen (CEA) level was 19.3 ng/ml (normal <5 ng/ml). A contrast enhanced ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) was performed for staging. Maximum intensity projection PET images revealed multiple ¹⁸F-FDG avid foci in the abdomen [Figure 1a, arrows]. PET-CT images reveal mildly enhancing ¹⁸F-FDG avid (maximum standardized uptake value [SUVmax]-10.3) circumferential wall thickening involving lower rectum and anorectal junction [Figure 1b and c, arrows], along with multiple ¹⁸F-FDG avid (SUVmax-4.2) mesorectal and pararectal nodes [Figure 1d and e, arrows]. Also, noted were multiple small and large ¹⁸F-FDG avid polyps in the colon [Figure 1f–i, arrows], largest in the descending colon [Figure 1i, SUVmax-6.5]. There were no distant metastases on PET-CT. The ¹⁸F-FDG avid colorectal polyps were reported as dysplastic with possible malignant transformation. A repeat colonoscopy was performed, and biopsy was performed specifically from the large hepatic flexure polyp and descending colon polyp mentioned in PET/CT report. Biopsy confirmed malignant transformation in both of them. The patient underwent total colectomy with nodal dissection and ileostomy, followed by adjuvant FOLFOX chemotherapy. The patient is doing fine at 6 months follow-up, with serum CEA of 2.1 ng/ml (normal <5 ng/ml).

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Figure 1 Maximum intensity projection positron emission tomography images revealed multiple ¹⁸F-fluorodeoxyglucose avid foci in the abdomen (a, arrows). Positron emission tomography-computed tomography images reveal mildly enhancing ¹⁸F-fluorodeoxyglucose avid circumferential wall thickening involving lower rectum and anorectal junction (b and c, arrows), along with multiple ¹⁸F-fluorodeoxyglucose avid mesorectal and pararectal nodes (d and e, arrows). Also noted were multiple small and large ¹⁸F-fluorodeoxyglucose avid polyps in the colon (f-i, arrows), largest in the descending colon (i)

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The presence of polyps is a risk factor for colorectal adenocarcinoma, and the risk is dependent on size, grade of dysplasia, and number of polyps.[12] Hence, conditions associated with multiple colorectal adenomas (MCRAs) are, therefore, the high risk for developing colorectal cancers. The most common polyposis disorders include familial adenomatous polyposis (FAP) and MCRAs syndromes.[34] In contrast to FAP who present at puberty and have positive family history, MCRAs patients usually present late in late fourth or fifth decade of life and might not have a family history, as in the present case.[5] The number of polyps is usually more than 10 but less than 100, while that in the case of FAP they are numerous (>100). Extra-colonic manifestations of FAP may be rarely present, though not seen in the present patient. Similar to FAP where it is always genetic associated with APC gene mutation, MCRA could be genetic but can be sporadic type well. Due to late presentation and lower risk of malignancy compared to FAP colon preserving surgery can be contemplated in MCRAs, while colectomy is the treatment of choice for FAP.[6] Unfortunately, in this patient, few other polyps also showed malignant degeneration and hence had to undergo total colectomy. The present case demonstrates the potential utility of ¹⁸F-FDG PET-CT for identifying malignant degeneration of polyps in patients with MCRAs[78] and thus accurately guiding the biopsy.