Resolution of Uptake on PET Scan after Removal of Large Colonic Polyps by Colonoscopy with EMR

Abstract

Purpose: Background: Colonic polyps are infrequently identified as an incidental finding on F-18 fluorodeoxyglucose positron emission tomography (PET) scan. We present 2 patients with large colonic polyps detected during whole-body PET for evaluation of lung nodules. Cases: An 82 year old female had a PET scan revealing focal uptake which correlated with a thickened loop of bowel. The standardized uptake value (SUV) in this area was as high as 6.5g/mL. Her previous colonoscopy 5 years prior was normal. Colonoscopy 3 months after the scan revealed a 40 mm sessile, carpet-like polyp in the transverse colon. Pathology reported a tubular adenoma with high grade dysplasia without invasion. During three sessions over 9 months, endoscopic mucosal resection (EMR) was performed using saline and epinephrine (1:10,000 mixture) for a lift-technique with piecemeal resection and argon plasma coagulation to treat the remaining tissue. Follow-up PET scan after 12 months revealed no metabolic activity in the colon. Repeat colonoscopy 5 months after the third resection demonstrated no lesions at the previous site, and multiple biopsies showed normal colonic mucosa. A 79 year old male had a PET scan showing focal uptake seen in the distal transverse colon with an SUV of 12.6 g/mL. Colonoscopy one month later revealed a 30 mm sessile, carpet-like polyp. Pathology reported a tubulovillous adenoma. EMR was performed with a combination of saline, epinephrine (1:10,000 mixture) and methylene blue for a lift-technique using a hot snare. The lesion was removed using a piecemeal resection. Argon plasma coagulation was used on the remaining tissue. PET scan for lung cancer 4 months later reported no metabolic activity in the colon. The patient declined colonoscopy after the normal PET. Discussion: PET is being increasingly used for surveillance after cancer treatment. This modality can incidentally detect pre-malignant lesions in the colon as well, with a sensitivity and specificity of nearly 75% and 80%, respectively. Accuracy is improved with larger size and higher grade of dysplasia of the lesion. It is a poor colorectal cancer screening tool, however, due to its limitations such as high cost and radiation exposure. EMR during colonoscopy can remove large, sessile polyps, preventing progression to malignancy. It is a desirable modality in patients with multiple comorbidities who are poor surgical candidates. These cases demonstrate the ability of colonoscopy with EMR to eradicate lesions identified by focal colonic uptake on PET.