The Diagnostic Value of Fluorine-18 Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography for the Detection of Surgical Site Infection After Spine Surgery

Tomohide Segawa, MD; Hisashi Koga, MD, PhD; Masahito Oshina, MD; Masayoshi Fukushima, MD; Hirohiko Inanami, MD

Disclosures

Spine. 2021;46(10):E602-E610. 

In This Article

Results

Patient Background Characteristics

Background characteristics for the 52 study subjects are shown in Table 1. The study subjects included more males than females. Majority of the patients (78.8%) received implant surgery. More than 60% of patients underwent F-18 FDG PET/CT during the early phase (within 12 weeks after the spine surgery). Among 52 patients who underwent F-18 FDG PET/CT based on suspected spinal infection, 29 and 21 patients were positive and negative for SSIs based on the final diagnosis, respectively (Supplemental Table 1, http://links.lww.com/BRS/B688). In addition to the method of pathogen detection in 29 SSI patients, diagnostic parameters such as fever, local swelling and redness, and purulent drainage are shown in Table 2.

Of the 29 SSI patients, 19 patients (65.5%) had fever, five patients (17.2%) had swelling and redness, and two patients (6.9%) had purulent drainage. There were no applicable diagnostic parameters in nine patients (31.0%). The pathogen test was performed in 21 patients (72.4%), and pathogens were identified in 13 patients (61.9%).

Diagnostic Performance of F-18 FDG PET/CT

Based on SUVmax data obtained from F-18 FDG PET/CT and final diagnosis for SSI, ROC analysis determined a cut off value of 5.0 for SUVmax (Figure 1). Both pattern-based diagnosis by nuclear medical physicians (Figure 2A and BB and 3A and B) and SUVmax-based diagnosis with cutoff value of 5.0 demonstrated excellent diagnostic yields with high sensitivity, specificity, and accuracy (pattern and SUVmax-based diagnoses: 97%, 100%, 98%, and 90%, 100%, 94%, respectively) (Table 3 and Supplemental Table 1, http://links.lww.com/BRS/B688). 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. SUVmax-based diagnosis tended to show lower sensitivity with three false-negative cases compared to the pattern-based diagnosis (one false-negative case), although there were no statistically significant differences in any parameters between the two diagnoses (sensitivity: P = 0.16, specificity: P = 1.00, positive predictive value [PPV]: P = 1.00, and negative predictive value [NPV]: P = 0.16).

Figure 1.

Receiver-operating characteristic (ROC) curve for the cut-off value of SUVmax.. ROC curve was generated based on the SUVmax data of 50 study subjects who underwent F-18 FDG PET/CT based on suspected SSIs. F-18 FDG PET/CT indicates fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography; FPF, false positive fraction; SSI, surgical site infection; SUVmax, maximal standardized uptake values; TPF, true positive fraction.

Figure 2.

Positive Case for Surgical Site Infection Based on Pattern-Based Diagnosis. Patient ID 18. F 18 FDG PET/CT and MRI were performed 4 weeks after the implant surgery. (A) Axial PET/CT scans at L4/5 and L5 levels. PET/CT showed FDG uptake around the intervertebral Peek cage and the left pedicle screw. (B) Axial T2-weighted magnetic resonance images at L4/5 and L5 levels. Artifacts of spinal implants rendered the magnetic resonance imaging unclear. F-18 FDG PET/CT indicates fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography.

Figure 3.

Negative case for surgical site infection based on pattern-based diagnosis. Patient ID 50. F-18 FDG PET/CT was performed 4 weeks after the implant surgery. (A) Coronal and sagittal PET/CT scans at L4, L4/5, and L5 levels. (B) Axial PET/CT scans at L4, L4/5, and L5 levels. None of PET/CT images reveal FDG uptake. F-18 FDG PET/CT indicates fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography.

SUVmax values were significantly higher in the patients with infection than those in the patients with no infection (7.5 ± 2.5 vs. 3.2 ± 0.7, respectively; P = 3.46 × 10−10, Figure 4). SUVmax values (patient IDs 2 and 3, SUVmax = 4.3 and 4.4, respectively) in two false-negative cases based on SUVmax-based diagnosis were relatively closed to the cutoff value of 5.0 (two red triangles in Figure 4). In contrast, SUVmax values in the single false negative cases based on both pattern- and SUVmax-based diagnoses was very low (Patient ID 1, SUVmax = 1.9, an orange square in Figure 4). Detailed observation in this false-negative case, this patient had received antibiotic treatment for 10 days before F-18 FDG PET/CT. Furthermore, she has medical history of central venous hyperalimentation after total gastric resection, suggesting increased susceptibility to infection.

Figure 4.

Individual SUVmax values in patients with/without infection. Patients are classified based on the final diagnosis into two groups: no infection and infection groups. Black circles indicate individual SUVmax values in patients accurately determined as either positive or negative based on F18-FDG PET/CT. An orange square indicates a false negative case based on both pattern- and SUVmax-based diagnoses. Two red triangles indicate false negative cases based on SUVmax-based diagnosis. Horizontal black bars indicate mean values. A light blue horizontal line indicates SUVmax cutoff value of 5.0. F-18 FDG PET/CT indicates fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography; SUVmax, maximal standardized uptake values.

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