Evaluating the Change in 18 F-Fluorodeoxyglucose Uptake in Perianal Fistulas on PET/CT over Time: A Serial Retrospective Analysis.

Rationale and Objectives: Perianal fistulas on ¹⁸ F-fluorodeoxyglucose positron emission tomography-computed tomography (FDG-PET/CT) can be an incidental site of FDG uptake in patients undergoing PET for other indications. There are no longitudinal studies describing FDG uptake patterns in perianal fistulas. Therefore, we aimed to analyze changes in FDG uptake over time in patients with incidental perianal fistulas.
Patients and Methods: Patients who underwent at least two FDG-PET/CTs between January 2011 and May 2023, with incidental perianal fistula, were retrospectively identified. We analyzed all sequential PET/CTs to determine the presence of a perianal fistula and recorded the fistula's maximum standardized uptake value (SUV _max ). Statistical analysis compared fistula FDG-avidity in the initial versus final PET/CT examinations and assessed the correlation between initial fistula SUV _max and percent change over time.
Results: The study included 15 fistulas in 14 patients, with an average of 5 PET/CT examinations per patient. The average interval between the first and last PET/CT was 24 months (range: 6-64). The average initial fistula SUV _max (11.28 ± 3.81) was significantly higher than the final fistula SUV _max (7.22 ± 3.99) (p = 0.0067). The fistula SUV _max declined by an average of 32.01 ± 35.33% with no significant correlation between initial fistula SUV _max and percent change over time (r = -0.213, p = 0.443, 95% CI -0.66-0.35).
Conclusion: FDG uptake in perianal fistulas shows temporal fluctuations but follows a decreasing SUV _max trend, possibly indicating a relationship with inflammatory activity. Further studies with larger cohorts paired with perianal fistula pelvic MR imaging are needed to validate these observations and their utility in guiding further management.
Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Dr. David H. Ballard reports a relationship with Takeda Pharmaceutical Company Limited that includes: funding grants. Dr. Parakkal Deepak reports a relationship with Janssen Pharmaceuticals Inc that includes: consulting or advisory and funding grants. Dr. Parakkal Deepak reports a relationship with Bristol Myers Squibb Co that includes: consulting or advisory and funding grants. Dr. Parakkal Deepak reports a relationship with Boehringer Ingelheim Pharmaceuticals Inc that includes: consulting or advisory and funding grants. Dr. Parakkal Deepak reports a relationship with AbbVie Inc that includes: consulting or advisory and funding grants. Dr. Parakkal Deepak reports a relationship with CorEvitas LLC that includes: consulting or advisory. Dr. Parakkal Deepak reports a relationship with Takeda Pharmaceuticals USA Inc that includes: consulting or advisory and funding grants. Dr. Parakkal Deepak reports a relationship with Sandoz Inc that includes: consulting or advisory. Dr. Parakkal Deepak reports a relationship with Landos Biopharma that includes: funding grants. Dr. Parakkal Deepak reports a relationship with Pfizer Inc that includes: consulting or advisory and funding grants. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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