title: Accuracy of FDG-PET/CT for Detection of Incidental Pre-Malignant and Malignant Colonic Lesions - Correlation with Colonoscopic and Histopathologic Findings.
abstract: OBJECTIVE
  We evaluated all PET/CTs acquired for patients without a primary diagnosis of colorectal cancer, and compared results for those who had subsequent colonoscopy within 6 months, to assess the accuracy of FDG PET/CT for detection of incidental pre-malignant polyps and malignant colon cancers.
  
  
  METHODS
  Medical records of 9,545 patients who underwent F-18 FDG PET/CT studies over 3.5 years were retrospectively reviewed. Due to pre-existing diagnosis of colorectal cancer, 818 patients were excluded. Of the remainder, 157 patients had colonoscopy within 6 months (79 males; mean age 61). We divided the colon into 4 regions and compared PET/CT results for each region with colonoscopy and histopathologic findings. True positive lesions included colorectal cancer, villous adenoma, tubulovillous adenoma, tubular adenoma and serrated hyperplastic polyp/hyperplastic polyposis.
  
  
  RESULTS
  Of 157 patients, 44 had incidental colonic uptake on PET/CT (28%). Of those, 25 had true positive (TP) uptake, yielding a 48% positive predictive value (PPV); 9% (4/44) were adenocarcinoma. There were 23 false positive (FP) lesions of which 4 were hyperplastic polyps, one was a juvenile polyp and 7 were explained by diverticulitis. Fifty eight patients had false negative PET scans but colonoscopy revealed true pre-malignant and malignant pathology, yielding 23% sensitivity. The specificity, negative predictive value (NPV) and accuracy were 96%, 90% and 87%, respectively. The average SUVmax values of TP, FP and FN lesions were 7.25, 6.11 and 2.76, respectively. There were no significant difference between SUVmax of TP lesions and FP lesions (p>0.95) but significantly higher than in FN lesions (p<0.001). The average size (by histopathology and colonoscopy) of TP lesions was 18.1 mm, statistically different from that of FN lesions which was 5.9 mm (p<0.001). Fifty-one percent of FN lesions were smaller than 5 mm (29/57) and 88% smaller than 10 mm (50/57).
  
  
  CONCLUSIONS
  The high positive predictive value of incidental focal colonic FDG uptake of 48% for colonic neoplasia suggests that colonoscopy follow-up is warranted with this finding. We observed a low sensitivity of standardly acquired FDG-PET/CT for detecting small polyps, especially those less than 5 mm. Clinicians and radiologists should be aware of the high PPV of focal colonic uptake reflecting pre-malignant and malignant lesions, and the need for appropriate follow up.
authors.affiliation: Division of Precision Medicine, Athinoula A Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA E-mail : anchisa@gmail.com.
authors.forename: Anchisa
authors.initials: A
authors.lastname: Kunawudhi
authors.forename: Alexandra K
authors.initials: AK
authors.lastname: Wong
authors.forename: Tarik K
authors.initials: TK
authors.lastname: Alkasab
authors.forename: Umar
authors.initials: U
authors.lastname: Mahmood
mesh_terms: D000230:Adenocarcinoma / Q000175:diagnosis / Q000473:pathology; D000236:Adenoma / Q000175:diagnosis / Q000473:pathology; D003106:Colon / Q000473:pathology*; D003110:Colonic Neoplasms / Q000175:diagnosis* / Q000473:pathology*; D003111:Colonic Polyps / Q000175:diagnosis / Q000473:pathology; D003113:Colonoscopy / Q000379:methods*; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000008:administration & dosage; D006801:Humans; D033162:Incidental Findings; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging / Q000379:methods; D000072078:Positron Emission Tomography Computed Tomography / Q000379:methods*; D049268:Positron-Emission Tomography / Q000379:methods; D019275:Radiopharmaceuticals / Q000008:administration & dosage; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18