Retrospective Study
Copyright ©The Author(s) 2022. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Clin Cases. Dec 6, 2022; 10(34): 12532-12542
Published online Dec 6, 2022. doi: 10.12998/wjcc.v10.i34.12532
Significance of incidental focal fluorine-18 fluorodeoxyglucose uptake in colon/rectum, thyroid, and prostate: With a brief literature review
Haejun Lee, Kyung-Hoon Hwang
Haejun Lee, Kyung-Hoon Hwang, Department of Nuclear Medicine, Gachon University College of Medicine, Gil Medical Center, Incheon 21565, South Korea
Author contributions: Lee H and Hwang KH contributed to this work, designed the research study, performed the research, analyzed the data, and wrote the manuscript; Lee H contributed analytic tools; All authors have read and approved the final manuscript.
Institutional review board statement: The study was reviewed and approved by the Institutional Review Board at our institution.
Informed consent statement: The requirement for informed consent was waived by the Institutional Review Board at our institution.
Conflict-of-interest statement: The authors declare that they have no conflicting interests.
Data sharing statement: The data that support the findings of this study are available from the corresponding author, [Hwang KH], upon reasonable request.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: https://creativecommons.org/Licenses/by-nc/4.0/
Corresponding author: Kyung-Hoon Hwang, MD, PhD, Professor, Nuclear Medicine, Gachon University College of Medicine, Gil Medical Center, Namdong-daero 774beon-gil, Namdong-gu, Incheon 21565, South Korea. forrest88@hanmail.net
Received: June 17, 2022
Peer-review started: June 17, 2022
First decision: July 29, 2022
Revised: August 10, 2022
Accepted: November 8, 2022
Article in press: November 8, 2022
Published online: December 6, 2022
Abstract
BACKGROUND

Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (F-18 FDG PET/CT), a functional imaging method, is usually performed on the entire torso, and regions of unexpected suspicious focal hypermetabolism are not infrequently observed. Among the regions, colon, thyroid, and prostate were found to be the common organs in a recent umbrella review. Some studies reported that a high rate of malignancy was shown in incidentally identified focal hypermetabolic regions and suggested that further examinations should not be ignored.

AIM

To investigate the malignancy rate of incidental focal FDG uptake, useful PET parameters and their cutoffs in discrimination between malignant and benign lesions.

METHODS

Retrospectively, the final reports of 16510 F-18 FDG PET/CT scans performed at our hospital between January 2016 and March 2022 were reviewed to identify incidentally observed FDG uptake in the colon/rectum, thyroid, and prostate. The scans of patients with current or prior malignancies at each corresponding location, without the final reports of histopathology or colonoscopy (for colon and rectum) for the corresponding hypermetabolic regions, or with diffuse (not focal) hypermetabolism were excluded. Finally, 88 regions of focal colorectal hypermetabolism in 85 patients (48 men and 37 women with mean age 67.0 ± 13.4 years and 63.4 ± 15.8 years, respectively), 48 focal thyroid uptakes in 48 patients (12 men and 36 women with mean age 62.2 ± 13.1 years and 60.8 ± 12.4 years, respectively), and 39 focal prostate uptakes in 39 patients (mean age 71.8 ± 7.5 years) were eligible for this study. For those unexpected focal hypermetabolic regions, rates of malignancy were calculated, PET parameters, such as standardized uptake value (SUV), capable of distinguishing between malignant and benign lesions were investigated, and the cutoffs of those PET parameters were determined by plotting receiver operating characteristic curves.

RESULTS

In the colon and rectum, 29.5% (26/88) were malignant and 33.0% (29/88) were premalignant lesions. Both SUVmax and SUVpeak differentiated malignant/premalignant from benign lesions, however, no parameters could distinguish malignant from premalignant lesions. Higher area under the curve was shown with SUVmax (0.752, 95%CI: 0.649-0.856, P < 0.001) and the cutoff was 7.6. In the thyroid, 60.4% (29/48) were malignant. The majority were well-differentiated thyroid cancers (89.7%, 26/29). The results of BRAF mutation tests were available for 20 of the 26 well-differentiated thyroid cancers and all 20 had the mutation. Solely SUVmax differentiated malignant from benign lesions and the cutoff was 6.9. In the prostate, 56.4% (22/39) were malignant. Only SUVmax differentiated malignant from benign lesions and the cutoff was 3.8. Overall, among the 175 focal hypermetabolic regions, 60.6% (106/175) were proven to be malignant and premalignant (in colon and rectum) lesions.

CONCLUSION

Approximately 60% of the incidentally observed focal F-18 FDG uptake in the colon/rectum, thyroid, and prostate were found to be malignant. Of the several PET parameters, SUVmax was superior to others in distinguishing between malignant/premalignant and benign lesions. Based on these findings, incidental focal hypermetabolism should not be ignored and lead physicians to conduct further investigations with greater confidence.

Keywords: Incidental, Focal, Uptake, Fluorine-18 fluorodeoxyglucose, Positron emission tomography/ computed tomography, Standardized uptake value

Core Tip: Unexpectedly identified uptake on fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (F-18 FDG PET/CT) is not a rare finding. Among the uptakes, focal uptake may have clinical implications by harboring malignant lesions. In this study, the clinical significance of the incidentally identified focal FDG uptake in the colon/rectum, thyroid, and prostate was investigated with the malignancy rate, comparison of PET parameters, and receiver operating characteristic curve. Overall, approximately up to 60% were malignancies (including premalignancy) for the regions and SUVmax was a superior PET parameter in discrimination between malignant/premalignant and benign lesions. The findings should lead physicians to conduct further investigations more confidently without ignoring the focal uptake.