Abstract and Introduction
Abstract
Study Design: Retrospective case series.
Objective: The purpose of this study was to assess the diagnostic yield of fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (F-18 FDG PET/CT) for surgical site infection (SSI) after spine surgery.
Summary of Background Data: Diagnosis of SSI in the spine based on F-18 FDG PET/CT requires experienced nuclear medical physicians for a detailed analysis of F-18 FDG distribution pattern. It has also been reported that increases in the maximal standardized uptake values of F-18 FDG (SUVmax) closely correlated with SSI, suggesting potential of more objective and quantitative diagnosis.
Methods: We assessed the diagnostic yield of F-18 FDG PET/CT (pattern-based diagnosis by nuclear medical physicians and SUVmax-based diagnosis) for SSI in 52 subjects who underwent spine surgery. The 52 subjects included 11 nonimplant and 41 implant cases. F-18 FDG PET/CT was performed in 33 and 19 cases in early (≤12 weeks after the surgery) and late (>12 weeks) phases, respectively. The final diagnosis of SSI was based on the results of pathogen identification, plain radiography, and CT and/or magnetic resonance imaging or response to antibiotics and/or reoperation.
Results: SUVmax-based diagnosis was performed with a cut off value of 5.0 as determined by receiver operating characteristic analysis. Both pattern-based and SUVmax-based diagnoses demonstrated excellent diagnostic yields with high sensitivity (97% and 90%), specificity (100% and 100%), and accuracy (98% and 94%). High diagnostic yields (accuracy of ≥90%) were consistently observed irrespective of presence or absence of implantation or interval between surgery and F-18 FDG PET/CT.
Conclusion: F-18 FDG PET/CT can be the procedure of choice for investigation of SSI in the spine when other imaging fails to provide a definitive diagnosis.
Level of Evidence: 4
Introduction
Surgical site infection (SSI) following spine surgery is an important complication that incurs significant morbidity and economic burden.[1–3] Infection rates range from 0.7% following minor surgical procedures to as high as 10% to 15% following complex instrumented spinal fusions and revision surgery.[4,5] A high level of suspicion is crucial to attain an early definitive diagnosis and initiate appropriate management.[1] The most common presenting symptom is back pain, usually manifesting 2 to 4 weeks and up to 3 months after a spinal procedure. Scheduling a follow-up visit between weeks 2 and 4 after surgery is, therefore, necessary for early detection. However, detecting SSI early remains a clinical challenge. Mild back pain is often the only clinical sign in early stages, especially in cases of deep infections. Moreover, blood tests such as white blood cell (WBC) count, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) are neither specific or sensitive.[6] Inflammatory markers are important diagnostic tools, and a comparison of pre- and postoperative levels should be performed when suspecting SSIs following spine surgery.
Magnetic resonance imaging (MRI) remains the diagnostic modality of choice when suspecting SSI following spine surgery.[1,2] Disadvantages of MRI include metal-induced artifacts, occasional nonspecific findings of osteomyelitis, and reduced sensitivity with short-term symptoms.[7] Another imaging technique as a diagnostic tool for detecting SSI is Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (F-18 FDG PET/CT). F-18 FDG PET/CT originally emerged as a significant molecular imaging technique in clinical oncology and cancer research; however, increased F-18 FDG uptake is not only observed in tumors but also in infections and inflammatory processes. Therefore, the imaging technique has been increasingly used in diagnosing infectious diseases.[1] Compared to MRI, one of the important advantages of F-18 FDG PET/CT is in the detection of metastatic infection.[7,8] In addition, F-18 FDG is not hindered by the presence of metallic implants. Thus, F-18 FDG PET/CT is recommended for assessing pyogenic spine infection when other imaging modalities fail to provide a definitive diagnosis or when patients do not respond as expected to antibiotic therapy.[9,10] Several studies have reported the usefulness of F-18 FDG PET or PET/CT for the diagnosis of spinal infections including implant-associated infection.[11–15]
Usually, diagnosis of SSI in the spine based on F-18 FDG PET/CT requires experienced nuclear medical physicians for a detailed analysis of the F-18 FDG distribution pattern.[9,14–17] It has been reported that increases in the maximum standardized uptake values (SUVmax) of F-18 FDG closely correlated with SSI in the spine, potentially enabling a more objective and quantitative diagnosis.[14,16] There are also some reports that indicate the limitation of F-18 FDG PET/CT for the diagnosis in the early phase after surgery due to nonspecific post-surgical inflammation and granulomatous tissue formation.[18,19] We also previously reported the usefulness of F-18 FDG PET/CT in diagnosing SSI after spine surgery in addition to a quantitative assessment utilizing SUVmax.[20] Our results showed that there was a statistically significant difference in SUVmax values (mean and range) between the SSI and control groups (9.0 and 5.5–14.7 vs. 3.3 and 2.0–4.3, respectively; P = 0.003). SUVmax was >5.0 in all patients with an SSI whereas less than 5.0 in all patients in the control group.
The limited study size with eight cases of infection in 14 subjects, however, precluded a robust quantitative analysis. In this study, we increased the sample size to 52 subjects and statistically determined the cutoff value of SUVmax based on the final diagnosis of SSI. We evaluated the diagnostic yields for F-18 FDG PET/CT pattern-based diagnosis by nuclear medicine physicians and SUVmax-based diagnosis in comparison with final diagnosis. In addition, we assessed the effects of presence or absence of implants and timing of F-18 FDG PET/CT (≤12 weeks after the surgery versus >12 weeks) on diagnostic yields.
Spine. 2021;46(10):E602-E610. © 2021 Lippincott Williams & Wilkins
