Focal Colonic FDG Activity with PET/CT: Guidelines for Recommendation of Colonoscopy

Abstract

Focal 18F-fluorodeoxyglucose (FDG) colonic activity can be incidentally seen in positron emission tomography/computed tomography (PET/CT) scans. Its clinical significance is still unclear. The purpose of this study was to assess the significance of focal FDG activity in PET/CT scans by correlating the imaging findings to colonoscopy results, and come up with some guidelines for recommendation of follow-up colonoscopy. A total of 133 patients who underwent both 18F-FDG PET/CT for different oncological indications and colonoscopy within 3 months were retrospectively studied. Imaging, colonoscopy and pathology results were analyzed. Of the 133 FDG-PET/CT scans, 109/133 (82%) did not show focal colonic FDG activity, and 24/133 (18%) did. Of the 109/133 PET/CTs without focal colonic FDG activity, 109/109 (100%) did not have evidence of colon cancer after colonoscopy and histology. Of the 24/133 PET/CTs with focal colonic FDG activity, 10/24 (42%) had pathologic confirmation of colon cancer and 14/24 (58%) did not have evidence of colon cancer after colonoscopy and histological analysis. Sensitivity was 10/10 (100%), specificity 109/123 (89%), positive predictive value (PPV) 10/24 (42%) and negative predictive value (NPV) 109/109 (100%). Incidental focal 18FDG activity in PET/CT imaging shows a high sensitivity, specificity and NPV for malignancy, with a not so high PPV of 42%. Although some people would argue that a 42% chance of malignancy justifies colonoscopy, this maybe is not possible in all cases. However, the high sensitivity of the test does not allow these studies to be overlooked. We provide our recommendations as per when to send patients with focal FDG colonic activity to have further characterization with colonoscopy.

Detection of incidental colorectal pathology on positron emission tomography/computed tomography

“…Our study included 148 patients with correlation of PET/CT and pathology results in a single institution, making it one of the largest studies to date to establish diagnosis and assess the significance of incidental focal colorectal 18 F‐FDG uptake on PET/CT. Previous studies have large sample sizes to look at the prevalence of incidental focal colorectal 18 F‐FDG uptake on PET/CT, but few had sufficient numbers who subsequently underwent colonoscopy . In addition, most patients in our study underwent colonoscopy within the first 2 months of PET/CT findings; hence, an accurate histological diagnosis was obtained.…”

“…Previous studies have large sample sizes to look at the prevalence of incidental focal colorectal 18 F-FDG uptake on PET/CT, but few had sufficient numbers who subsequently underwent colonoscopy. 8,10,11 In addition, most patients in our study underwent colonoscopy within the first 2 months of PET/CT findings; hence, an accurate histological diagnosis was obtained. Finally, our institution maintained a centralized electronic medical records system since the early 2000s, which allowed us to comprehensively review all patient history, imaging results, colonoscopy reports and pathology results.…”

“…A common site is the large bowel, where the prevalence of incidental focal colorectal 18 F‐FDG uptake detected by PET or PET/CT is estimated at 3.6% . While diffuse and segmental patterns of 18 F‐FDG uptake are attributed to benign or inflammatory causes, focal uptake is associated with a significant risk of neoplasia . Given that colorectal cancer may be insidious in onset and run a silent course until late, these radiological findings should not be ignored .…”

“…3 While diffuse and segmental patterns of 18 F-FDG uptake are attributed to benign or inflammatory causes, focal uptake is associated with a significant risk of neoplasia. [4][5][6][7][8][9][10][11] Given that colorectal cancer may be insidious in onset and run a silent course until late, these radiological findings should not be ignored. 12 Prompt diagnosis may have a significant impact on patient outcome, particularly in these patients who already has a pre-existing cancer, as it may necessitate a management plan that integrates treatment for both cancers within a relatively short period of time.…”

FDG PET/CT Pitfalls in Gynecologic and Genitourinary Oncologic Imaging

“…Physiologic activity within the bowel is typically diffuse and linear, whereas pathologic uptake is often focal. The pattern of focal colonic FDG uptake has a high sensitivity, specificity, and negative predictive value for colonic malignancy, but a lower positive predictive value for the same (32). Focal activity can also occur with premalignant polyps and benign inflammatory conditions such as inflamed diverticula, hemorrhoids, and focal colitis (33,34).…”