18F-FDG-PET/CT better localizes active spinal infection than MRI for successful minimally invasive surgery

Imaging of Spondylodiscitis: An Update

Spondylodiscitis is an infection of the vertebral body and/or intervertebral disc, which can also involve the epidural space, posterior elements, and paraspinal soft tissues. Due to high morbidity and mortality, prompt diagnosis and treatment of spondylodiscitis is critical. However, diagnosis can be challenging due to nonspecific signs and symptoms. Magnetic resonance imaging with and without contrast is the imaging modality of choice due to high sensitivity and specificity. Intravenous administration of gadolinium contrast can better demonstrate the extent of soft tissue and bone abscesses. However, magnetic resonance imaging is less useful in the evaluation of treatment response. When magnetic resonance imaging cannot be performed or is not diagnostic, radionuclide imaging is a useful alternative. Although bone scintigraphy frequently is used as a screening test, false negative results can occur early in the course of the infection and in the elderly. This test is not useful for detecting the soft tissue infections that often accompany or mimic spondylodiscitis. Gallium-67 citrate improves the specificity of the bone scan, can detect infection earlier than the bone scan, may be more sensitive, especially in elderly patients, and identifies accompanying soft tissue infection. Performing SPECT and SPECT/CT improve accuracy. The 2-3 day delay between radiopharmaceutical administration, poor image quality, and relatively high patient radiation dose are significant disadvantages of gallium-67. Furthermore gallium-67 is no longer as readily available as it once was. ¹⁸F-FDG imaging is the radionuclide test of choice for spondylodiscitis. The procedure, completed in one day, is sensitive, has a high negative predictive value, and reliably differentiates degenerative from infectious vertebral body end-plate abnormalities. ¹⁸F-FDG has outperformed bone and gallium-67 imaging in comparative studies. ¹⁸F-FDG may be able to provide an objective means for monitoring response to treatment. The potential of other agents for diagnosing spondylodiscitis has been studied. Although indium-111biotin accurately diagnoses spondylodiscitis, this radiopharmaceutical has never been commercially available. Gallium-68 citrate and ^99mTc-radiolabeled antimicrobial peptides have been investigated, but their role in the diagnosis of spondylodiscitis has not been established. Labeled leukocyte scintigraphy has no role in the diagnosis of spondylodiscitis.

Imaging of Spine Infections

The incidence of spondylodiskitis has increased over the last 20 years worldwide, especially in the immunodepressed population, and it remains a complex pathology, both in terms of diagnosis and treatment. Because clinical symptoms are often nonspecific and blood culture negative, imaging plays an essential role in the diagnostic process. Magnetic resonance imaging, in particular, is the gold standard technique because it can show essential findings such as vertebral bone marrow, disk signal alteration, a paravertebral or epidural abscess, and, in the advanced stage of disease, fusion or collapse of the vertebral elements. However, many noninfectious spine diseases can simulate spinal infection. In this article, we present imaging features of specific infectious spine diseases that help radiologists make the distinction between infectious and noninfectious processes.

Positron emission tomography-magnetic resonance imaging as a research tool in musculoskeletal conditions

Compared to positron emission tomography/computed tomography (PET/CT), the uptake of PET- magnetic resonance imaging (MRI) has been slow, even more so in clinical practice compared to the (pre-)clinical research setting. However, for applications in musculoskeletal (MSK) research, the combination of PET and MRI into a single modality offers attractive advantages over other imaging modalities. Most importantly, MRI has exquisite soft-tissue detail without the use of contrast agents or ionizing radiation, superior bone marrow visualization, and an extensive spectrum of distinct multiparametric assessment methods. In the preclinical setting, the introduction of PET inserts for small-animal MRI machines has proven to be a successful concept in bringing this technology to the lab. Initial hurdles in quantification have been mainly overcome in this setting. In parallel, a promising range of radiochemistry techniques has been developed to create multimodality probes that offer the possibility of simultaneously querying different metabolic pathways. Not only will these applications help in elucidating disease mechanisms, but they can also facilitate drug development. The clinical applications of PET/MRI in MSK are still limited, but encouraging initial results with novel radiotracers suggest a high potential for use in various MSK conditions, including osteoarthritis, rheumatoid arthritis, ankylosing spondylitis and inflammation and infection. Further innovations will be required to bring down the cost of PET/MRI to justify a broader clinical implementation, and remaining issues with quality control and standardization also need to be addressed. Nevertheless, PET/MRI is a powerful platform for MSK research with distinct qualities that are not offered by other techniques.

Diagnosis of vertebral osteomyelitis

Native vertebral osteomyelitis (NVO) is a potentially fatal infection which has seen a gradual increase in its incidence over the past decades. The infection is insidious, presenting with symptoms of back pain. Fever is present in about 60 % of patients. Prompt diagnosis of NVO is important to prevent the development of complications. Numerous laboratory and imaging tools can be deployed to accurately establish the diagnosis. Imaging techniques such as magnetic resonance, nuclear imaging, and computed tomography are essential in diagnosing NVO but can also be useful in image-guided biopsies. Laboratory tools include routine blood tests, inflammatory markers, and routine culture techniques of aspirated specimens. Recent advances in molecular techniques can assist in identifying offending pathogen(s). In this review, we detail the arsenal of techniques that can be utilized to reach a diagnosis of NVO.

Lack of Clinical Utility of Labeled White Blood Cell Scintigraphy in Patients with Fever of Unknown Origin

Background

Labeled white blood cell scintigraphy (WBCS) has been used for over 40 years to localize an infection source in patients with fever of unknown origin (FUO). It continues to be in widespread use for such patients in modern times, despite the tremendous advances in modern radiological imaging and laboratory medicine.

Methods

We critically evaluated the clinical contribution of WBCS performed in 132 patients with FUO at 7 hospitals from mid-2015 to the end of 2019. For each patient, all radiographic and laboratory results and all electronic clinical notes were carefully evaluated as many days before and after the scan as necessary to arrive at a final diagnosis.

Results

Although 50 WBCS (38%) showed positive findings, the majority of these were false positive (FP). Of the 19 true-positive (TP) scans, most were already known or about to become known by tests already ordered at the time of the scan. Only 2 TP scans (1.5%) contributed to the final diagnosis, and these did so only indirectly. FP scans led to 7 unnecessary procedures.

Conclusions

In FUO patients for whom an infection source is not discovered following an appropriate radiographic and laboratory workup, WBCS is not a useful procedure.

The development of musculoskeletal radiology for 100 years as presented in the pages of Acta Radiologica

During the last 100 years, musculoskeletal radiology has developed from bone-only radiography performed by everyone to a dedicated subspecialty, still secure in its origins in radiography but having expanded into all modalities of imaging. Like other subspecialties in radiology, it has become heavily dependent on cross-sectional and functional imaging, and musculoskeletal interventions play an important role in tumor diagnosis and treatment and in joint diseases. All these developments are reflected in the pages in Acta Radiologica, as shown in this review.

Total-Body PET Imaging of Musculoskeletal Disorders

Imaging of musculoskeletal disorders, including arthritis, infection, osteoporosis, sarcopenia, and malignancies, is often limited when using conventional modalities such as radiography, computed tomography (CT), and MR imaging. As a result of recent advances in Positron Emission Tomography (PET) instrumentation, total-body PET/CT offers a longer axial field-of-view, higher geometric sensitivity, and higher spatial resolution compared with standard PET systems. This article discusses the potential applications of total-body PET/CT imaging in the assessment of musculoskeletal disorders.

Comparison of MRI, [18F]FDG PET/CT, and 99mTc-UBI 29-41 scintigraphy for postoperative spondylodiscitis-a prospective multicenter study

Purpose

Postoperative infection still constitutes an important complication of spine surgery, and the optimal imaging modality for diagnosing postoperative spine infection has not yet been established. The aim of this prospective multicenter study was to assess the diagnostic performance of three imaging modalities in patients with suspected postoperative spine infection: MRI, [¹⁸F]FDG PET/CT, and SPECT/CT with ^99mTc-UBI 29-41.

Methods

Patients had to undergo at least 2 out of the 3 imaging modalities investigated. Sixty-three patients enrolled fulfilled such criteria and were included in the final analysis: 15 patients underwent all 3 imaging modalities, while 48 patients underwent at least 2 imaging modalities (MRI + PET/CT, MRI + SPECT/CT, or PET/CT + SPECT/CT). Final diagnosis of postoperative spinal infection was based either on biopsy or on follow-up for at least 6 months. The MRI, PET/CT, and SPECT/CT scans were read blindly by experts at designated core laboratories. Spine surgery included metallic implants in 46/63 patients (73%); postoperative spine infection was diagnosed in 30/63 patients (48%).

Results

Significant discriminants between infection and no infection included fever (P = 0.041), discharge at the wound site (P < 0.0001), and elevated CRP (P = 0.042). There was no difference in the frequency of infection between patients who underwent surgery involving spinal implants versus those who did not. The diagnostic performances of MRI and [¹⁸F]FDG PET/CT analyzed as independent groups were equivalent, with values of the area under the ROC curve equal to 0.78 (95% CI: 0.64–0.92) and 0.80 (95% CI: 0.64–0.98), respectively. SPECT/CT with ^99mTc-UBI 29-41 yielded either unacceptably low sensitivity (44%) or unacceptably low specificity (41%) when adopting more or less stringent interpretation criteria. The best diagnostic performance was observed when combining the results of MRI with those of [¹⁸F]FDG PET/CT, with an area under the ROC curve equal to 0.938 (95% CI: 0.80–1.00).

Conclusion

[¹⁸F]FDG PET/CT and MRI both possess equally satisfactory diagnostic performance in patients with suspected postoperative spine infection, the best diagnostic performance being obtained by combining MRI with [¹⁸F]FDG PET/CT. The diagnostic performance of SPECT/CT with ^99mTc-UBI 29-41 was suboptimal in the postoperative clinical setting explored with the present study.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-020-05109-x.

Role of 18F-flurodeoxyglucose in orthopaedic implant-related infection: review of literature and experience

Infection and inflammation are a common occurrence with orthopaedic procedures. Anatomical modalities can show the transformation in the disease process; however, these may occur later when compared with functional imaging modalities that are more likely to identify early disease patterns. Various molecular imaging modalities such as three-phase bone scintigraphy, labelled leucocyte scintigraphy, as well as radiolabelled antibiotics and immunoglobulins have been considered and have played key roles in assisting clinical decision-making. While 18F-flurodeoxyglucose (FDG) PET/computed tomography (CT) has been relatively well established in cancer pathways, it has the potential to contribute to surgical decision making for possible osteomyelitis post-metal implant surgery. In this article, we present a review of recently used tracers, and share our experience with using 18F-FDG PET/CT studies in a few diverse clinical settings related to post-metal implant osteomyelitis.

Diagnostic performance of 18F-FDG PET/CT in patients with spinal infection: a systematic review and a bivariate meta-analysis

PURPOSE

Diagnosis of spinal infection (SI) is challenging and usually requires multiple tests. We aimed to perform a systematic review and a bivariate meta-analysis on the diagnostic role of ¹⁸F-FDG PET/CT in patients with SI.

METHODS

A comprehensive literature search of studies published through February 2019 in PubMed/MEDLINE and Cochrane library databases was carried out. Studies investigating the diagnostic performance of ¹⁸F-FDG PET/CT in patients with SI were eligible for inclusion in the qualitative analysis. For the quantitative analysis, pooled sensitivity, specificity, positive and negative likelihood ratio (LR+ and LR-) and diagnostic odds ratio (DOR) of ¹⁸F-FDG PET/CT in patients with suspected SI were calculated on a per examination-based analysis. Pooled data were presented with 95% confidence intervals (95% CI).

RESULTS

Twenty-six articles (833 patients) using ¹⁸F-FDG PET/CT were eligible for the qualitative analysis. Twelve studies (396 patients) were selected for the meta-analysis. Overall, ¹⁸F-FDG PET/CT demonstrated a very good diagnostic performance in patients with SI and several studies underlined the value of ¹⁸F-FDG PET/CT in assessing the response to treatment. The bivariate meta-analysis on ¹⁸F-FDG PET/CT in patients with suspected SI provided the following results: sensitivity 94.8% (95% CI 88.9-97.6%) and specificity 91.4% (95% CI 78.2-96.9%). The pooled LR+, LR- and DOR were 4.7 (95% CI 2.9-7.7), 0.11 (95% CI 0.07-0.16) and 63.4 (95% CI 28.9-139), respectively. No significant heterogeneity or publication bias was found.

CONCLUSION

¹⁸F-FDG PET/CT demonstrated a very good diagnostic performance in patients with SI and can be used in patients in which MRI cannot be performed or is non-diagnostic or inconclusive. Several studies underlined the value of ¹⁸F-FDG PET/CT in assessing the response to treatment in patients with SI. Overall, larger multicentre and prospective studies and cost-effectiveness analyses are warranted.

Retrospective study to evaluate the clinical significance of a second rise in C-reactive protein level following instrumented spinal fusion surgery

BACKGROUND

This study aimed to identify the incidence and causes of a second rise in C-reactive protein (CRP) levels following spinal instrumentation surgery and to help determine how an abnormal CRP response should be interpreted and managed during postoperative care.

METHODS

The medical records of 948 patients who underwent instrumented spine fusion surgery and met the inclusion criteria were retrospectively reviewed to assess the frequency and causes of a second rise (SR) of CRP. A SR of CRP was defined when the CRP level after postoperative day 7 increased by more than 0.5 mg/dl from that at the previous time-point. The diagnostic cut-off value of CRP elevation for detection of surgical site infection (SSI) was determined. Cut-off values were analyzed using receiver operating characteristic (ROC) curves. Bayes' theorem was used to determine blood test posterior probabilities for SSI-positive cases using cutoff values of re-evaluated CRP levels.

RESULTS

SR of CRP occurred in 107 of the 948 patients. Of the patients with SR of CRP, 38 (35%) patients had developed SSI, 33 (31%) patients had causes other than SSI, and the remaining 36 patients had unidentified causes. Among the patients with SR, excluding those with causes other than SSI, the best diagnostic cut-off value of SR for detection of SSI was 3.04 mg/dl (area under the curve was 0.74). The posterior test probability was 84.4%.

CONCLUSIONS

For patients with SR of CRP, who had no causes other than SSI, an SR value of 3.04 mg/dl correlated with a high probability of developing SSI.

FDG PET/CT of Infection: Should It Replace Labeled Leukocyte Scintigraphy of Inpatients?

OBJECTIVE. The purpose of this study was to compare the sensitivity, specificity, and helpfulness to referring clinicians of labeled leukocyte scintigraphy versus FDG PET/CT in inpatients with suspected infection. MATERIALS AND METHODS. In this retrospective study, labeled leukocyte scintigraphy and FDG PET/CT examinations performed from 2009 to 2017 for suspected infection in inpatients were identified. Sensitivity, specificity, and helpfulness of PET/CT versus labeled leukocyte scintigraphy were calculated by means of a mixed generalized linear model. Number of yearly tests and radiopharmaceutical costs were also assessed. RESULTS. Fifty-seven patients (30 men, 27 women; median age, 65 years; range, 21-91 years) underwent whole-body labeled leukocyte scintigraphy. Forty-two patients (30 male patients, 12 female patients; median age, 62.5 years; range, 12-91 years) underwent PET/CT for suspected infection. Labeled leukocyte scintigraphy was 66.7% sensitive, whereas the sensitivity of PET/CT was 89.7% (p = 0.0485). The higher sensitivity of PET/CT did not come at a cost to specificity, which was 73.3% as opposed to 76.9% for labeled leukocyte scintigraphy (p = 0.8050). The odds of a positive study being helpful increased 4.6-fold for PET/CT versus labeled leukocyte scintigraphy (p = 0.0412). From 2009 to 2011, 33 labeled leukocyte scintigraphic examinations were performed versus two PET/CT examinations; and from 2012 to 2014, 16 labeled leukocyte scintigraphic versus 22 PET/CT examinations; from 2015 to 2017, eight labeled leukocyte scintigraphic versus 18 PET/CT examinations. The cost of labeled leukocytes increased between 2009 and 2017, but that of FDG decreased. By 2017, a labeled leukocyte radiopharmaceutical dose was approximately 10 times the cost of an FDG dose. CONCLUSION. PET/CT was more sensitive than and as specific as labeled leukocyte scintigraphy for identifying a source of infection in inpatients, and it was more helpful to referring clinicians. Use of PET/CT increased over time and was associated with substantial savings in radiopharmaceutical cost.

Joint EANM/ESNR and ESCMID-endorsed consensus document for the diagnosis of spine infection (spondylodiscitis) in adults

PURPOSE

Diagnosis of spondylodiscitis (SD) may be challenging due to the nonspecific clinical and laboratory findings and the need to perform various diagnostic tests including serologic, imaging, and microbiological examinations. Homogeneous management of SD diagnosis through international, multidisciplinary guidance would improve the sensitivity of diagnosis and lead to better patient outcome.

METHODS

An expert specialist team, comprising nuclear medicine physicians appointed by the European Association of Nuclear Medicine (EANM), neuroradiologists appointed by the European Society of Neuroradiology (ESNR), and infectious diseases specialists appointed by the European Society of Clinical Microbiology and Infectious Diseases (ESCMID), reviewed the literature from January 2006 to December 2015 and proposed 20 consensus statements in answer to clinical questions regarding SD diagnosis. The statements were graded by level of evidence level according to the 2011 Oxford Centre for Evidence-based Medicine criteria and included in this consensus document for the diagnosis of SD in adults. The consensus statements are the result of literature review according to PICO (P:population/patients, I:intervention/indicator, C:comparator/control, O:outcome) criteria. Evidence-based recommendations on the management of adult patients with SD, with particular attention to radiologic and nuclear medicine diagnosis, were proposed after a systematic review of the literature in the areas of nuclear medicine, radiology, infectious diseases, and microbiology.

RESULTS

A diagnostic flow chart was developed based on the 20 consensus statements, scored by level of evidence according to the Oxford Centre for Evidence-based Medicine criteria.

CONCLUSIONS

This consensus document was developed with a final diagnostic flow chart for SD diagnosis as an aid for professionals in many fields, especially nuclear medicine physicians, radiologists, and orthopaedic and infectious diseases specialists.

Comparing the Diagnostic Accuracies of F-18 Fluorodeoxyglucose Positron Emission Tomography and Magnetic Resonance Imaging for the Detection of Spondylodiscitis: A Meta-analysis

STUDY DESIGN

A meta-analysis.

OBJECTIVE

The aim of this study was to compare the diagnostic accuracies of F-18 fluorodeoxyglucose (F-18 FDG) positron emission tomography (PET) and magnetic resonance imaging (MRI) for the detection of spondylodiscitis through a meta-analysis.

SUMMARY OF BACKGROUND DATA

There is no meta-analysis study that compares the diagnostic accuracies of F-18 FDG PET and MRI for the detection of spondylodiscitis.

METHODS

The MEDLINE and EMBASE databases were searched from the earliest available date of indexing to January 10, 2018 for studies comparing the diagnostic performance F-18 FDG PET with that of MRI for the detection of spondylodiscitis. We determined the sensitivities and specificities across studies, calculated the positive and negative likelihood ratios (LR+ and LR-), and constructed the summary receiver operating characteristic curves.

RESULTS

In the seven studies (212 patients) selected, the pooled sensitivity and specificity of F-18 FDG PET were 0.95 (95% confidence interval [CI]: 0.87-0.98) and 0.88 (95% CI: 0.73-0.95), respectively. The LR syntheses showed an overall LR+ of 7.6 (95% CI: 3.4-17.2) and LR- of 0.05 (95% CI: 0.02-0.14). The pooled diagnostic odds ratio was 141 (95% CI: 44-444). The pooled sensitivity and specificity of MRI were 0.85 (95% CI: 0.65-0.95) and 0.66 (95% CI: 0.48-0.80), respectively. The LR syntheses showed an overall LR+ of 2.5 (95% CI: 1.5-4.2) and LR- of 0.22 (95% CI: 0.08-0.60). The pooled diagnostic odds ratio was 11 (95% CI: 3-42). In the meta-regression analysis, no variable was identified as the source of the study heterogeneity.

CONCLUSION

The current meta-analysis shows that F-18 FDG PET has better diagnostic accuracy than MRI for the detection of spondylodiscitis. Further large multicenter studies would be necessary to substantiate the diagnostic accuracies of F-18 FDG PET and MRI for spondylodiscitis.

LEVEL OF EVIDENCE

2.

Added value of [18F]fluorodeoxyglucose positron emission tomography/computed tomography for the diagnosis of post-operative instrumented spine infection

PURPOSE

Post-operative instrumented spine infection (PISI) is an infrequent complication. Diagnosis of spinal implant infection can be difficult, especially in case of chronic infection.

METHODS

This retrospective study attempts to evaluate the diagnostic performance of [¹⁸F]fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) in PISI. Imagings were performed between April 2010 and June 2018 among patients referred for suspected chronic spinal implant infection. PET/CT were performed more than 12 weeks after surgery. PET/CT images were re-interpreted independently by two nuclear medicine physicians without knowledge of the patient's conditions. PET/CT data were analyzed both visually and semi-quantitatively (SUV_max). MRI results were collected from medical records. The final diagnosis of infection was based on bacteriological cultures or a twelve-month follow-up.

RESULTS

Forty-nine PET/CT were performed in 44 patients (22 women, median age 65.0 years). Twenty-two patients had a diagnosis of infection during follow-up. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for PET/CT were 86.4%, 81.5%, 79.2%, and 88.0%. Sensitivity, specificity, PPV and NPV were 66.7%, 75.0%, 66.0%, 75.0% respectively for MRI and 50.0%, 92.6%, 84.6% and 69.4% for serum C-reactive protein (CRP). Although these values were higher for PET/CT than for MRI or CRP, the differences were not statistically significant. In this setting, false positives with PET/CT can be observed in case of previous spine infection or adjacent segments disc disease. False negatives can result of extensive instrumented arthrodesis or infection with low virulence bacteria.

CONCLUSION

PET/CT is useful for the diagnosis of PISI. These results should be evaluated in further prospective study.

Postoperative Spine Infection: Diagnosis and Management

STUDY DESIGN

Review article.

OBJECTIVES

A review of the literature on postoperative spinal infections, their diagnosis, and management.

METHODS

A systematic computerized Medline literature search was performed using PubMed, Cochrane Database of Systematic Reviews, and EMBASE. The electronic databases were searched for publication dates from the last 10 years. The searches were performed from Medical Subject Headings (MeSH) used by the National Library of Medicine. Specifically, MeSH terms "spine," "infections," "management," and "diagnosis" were used.

RESULTS

Currently, the gold standard for diagnosis of postoperative spine infection is positive deep wound culture. Many of the current radiologic and laboratory tests can assist with the initial diagnosis and monitoring treatment response. Currently erythrocyte sedimentation rate, C-reactive protein, computed tomography scan, and magnetic resonance imaging with and without contrast are used in combination to establish diagnosis. Management of postoperative spine infection involves thorough surgical debridement and targeted antibiotic therapy.

CONCLUSIONS

Postoperative spine infection is a not uncommon complication following surgery that may have devastating consequences for a patient's short- and long-term health. A high index of suspicion is needed to make an early diagnosis.

Diagnostic value of FDG-PET versus magnetic resonance imaging for detecting spondylitis: a systematic review and meta-analysis

BACKGROUND CONTEXT

Spondylitis is a rare infection in bone requiring multiple diagnostic strategies for verification.

PURPOSE

This study aimed to compare the diagnostic values of ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) and magnetic resonance imaging (MRI) in detecting spondylitis.

METHODS

Online PubMed, Embase, and Cochrane Library databases were systematically searched through September 2017 for studies comparing the diagnostic values of ¹⁸F-FDG-PET and MRI. The summary sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR), and summary receiver operating characteristic (SROC) curve were calculated using Stata software. The ratio of these indexes between ¹⁸F-FDG-PET and MRI was also determined.

RESULTS

The summary results for ¹⁸F-FDG-PET were as follows: sensitivity=0.96 [95% confidence intervals (CI), 0.84-0.99]; specificity=0.90 (95% CI, 0.79-0.96); PLR=9.83 (95% CI, 4.39-22.03); NLR=0.05 (95% CI, 0.01-0.19); DOR=124.08 (95% CI, 39.04-394.34); and area under the SROC=0.97 (95% CI, 0.95-0.98). The summary sensitivity, specificity, PLR, NLR, DOR, and area under the SROC for MRI were 0.76 (95% CI, 0.65-0.84), 0.62 (95% CI, 0.45-0.77), 2.01 (95% CI, 1.36-2.98), 0.39 (95% CI, 0.27-0.56), 5.08 (95% CI, 2.66-9.69), and 0.77 (95% CI, 0.73-0.80), respectively. The summary results of sensitivity (p=.034), specificity (p=.006), PLR (p<.001), DOR (p<.001), and area under the SROC (p<.001) were higher in ¹⁸F-FDG-PET than in MRI. However, NLR (p=.003) was lower in ¹⁸F-FDG-PET than in MRI.

CONCLUSIONS

¹⁸F-FDG-PET had a higher diagnostic value compared with MRI in detecting spondylitis.

18F-FDG-PET/CT localizes intervertebral disc space infection following posterior lumbar interbody fusion surgery leading to successful retention of percutaneously inserted pedicle screws: a case report

Introduction

Postoperative infection is a potentially devastating complication of spine surgery and an appropriate strategy and timely decision-making are essential for successful treatment of deep surgical site infection (SSI) after spinal instrumentation surgeries. However, there is a lack of consensus on implant removal or retention. We report on a case of deep SSI after posterior lumbar interbody fusion (PLIF) surgery in which we achieved clinical cure by debridement and removal of the interbody fusion cage without removing the percutaneously inserted pedicle screws (PPS).

Case presentation

A case was a 53-year-old woman with deep SSI after PLIF surgery using the PPS system at the L4-5 level. Computed tomography (CT) showed no clear radiolucent line around the screws and 18F-fluorodeoxyglucose positron emission tomography (FDG-PET)/CT demonstrated abnormal FDG uptake around the cages and no uptake around the pedicle screws. Intervertebral cages were removed and iliac bone grafts were inserted between the vertebral bodies, without removing the pedicle screws. The infection was cleared and bone fusion was achieved after the revision surgery.

Discussion

Targeting active infection using FDG-PET/CT is considered useful in narrowing the surgical margins and determining whether to preserve instrumentation in revision surgery after SSI. PLIF using the PPS system could be useful in preventing the easy spread of infection from the intervertebral space to the insertion point of PPS through the interstitial space.

Imaging of Spondylodiscitis

Spondylodiscitis is an infection of the vertebral body or disc and may also involve the epidural space, posterior elements, and paraspinal soft tissues. It is a cause of morbidity and mortality, and warrants early diagnosis and prompt treatment. Diagnosis can be difficult because of nonspecific signs and symptoms. Magnetic resonance imaging is sensitive and specific and is the imaging modality of choice for spondylodiscitis. Gadolinium contrast can show the extent of soft tissue and bone phlegmon and abscess. The test is less useful for evaluating treatment response. When magnetic resonance imaging cannot be performed or is not diagnostic, radionuclide imaging is a useful alternative. Although bone scintigraphy frequently is used as a screening test, false-negative results can occur, especially in the elderly. This test is not useful for detecting soft tissue infections that accompany or mimic spondylodiscitis. Gallium-67 citrate improves the specificity of the bone scan, can detect infection earlier than the bone scan, may be more sensitive, especially in elderly patients, and identifies accompanying soft tissue infection. Performing SPECT and SPECT/CT improves accuracy. The 2- to 3-day delay between radiopharmaceutical administration and the relatively poor image quality are significant disadvantages of gallium-67. Indium-111 biotin, alone or in combination with streptavidin, accurately diagnoses spondylodiscitis; unfortunately, this agent is not widely available. Currently, ¹⁸F-FDG imaging is the radionuclide test of choice for spondylodiscitis. The procedure, which is completed in a single session, is sensitive, has a high negative predictive value, and reliably differentiates degenerative from infectious vertebral body end plate abnormalities. In comparative investigations, ¹⁸F-FDG has outperformed bone and gallium-67 imaging. Preliminary data suggest that ¹⁸F-FDG may be able to provide an objective means to measure response to treatment. Gallium-68 citrate and 99mTc-radiolabeled antimicrobial peptides have been investigated, but their role in spondylodiscitis has yet to be established.

Radionuclide Imaging of Musculoskeletal Infection: A Review

There are numerous imaging tests for diagnosing musculoskeletal infection. Radiographs are routinely performed, because even when not diagnostic, they provide an anatomic overview of the region of interest that could influence subsequent procedure selection and interpretation. MRI is sensitive and provides superb anatomic detail. Bone scintigraphy accurately diagnoses osteomyelitis in bones not affected by underlying conditions. (67)Ga is used primarily for spondylodiskitis. Although in vitro labeled leukocyte imaging is the radionuclide test of choice for complicating osteomyelitis such as diabetic pedal osteomyelitis and prosthetic joint infection, it is not useful for spondylodiskitis. Antigranulocyte antibodies and antibody fragments have limitations and are not widely available. (111)In-biotin is useful for spondylodiskitis. Radiolabeled synthetic fragments of the antimicrobial peptide ubiquicidin are promising infection-specific agents. (18)F-FDG is the radiopharmaceutical of choice for spondylodiskitis. Its role in diabetic pedal osteomyelitis and prosthetic joint infection is not established. Preliminary data suggest (68)Ga may be useful in musculoskeletal infection. (124)I-fialuridine initially showed promise as an infection-specific radiopharmaceutical, but subsequent investigations were disappointing. The development of PET/CT and SPECT/CT imaging systems, which combine anatomic and functional imaging, has revolutionized diagnostic imaging. These hybrid systems are redefining the diagnostic workup of patients with suspected or known infection and inflammation by improving diagnostic accuracy and influencing patient management.

Use of Simultaneous 18F-FDG PET/MRI for the Detection of Spondylodiskitis

The diagnosis of spondylodiskitis is often challenging. MRI is quite sensitive but lacks specificity, and distinction from erosive osteochondritis is often difficult. We sought to assess the diagnostic value of (18)F-FDG PET combined with MRI (combined (18)F-FDG PET/MRI) in patients with suspected spondylodiskitis and an inconclusive clinical or MRI presentation.

METHODS

In a prospective study, 30 patients with previous inconclusive MRI results and suspected spondylodiskitis underwent combined (18)F-FDG PET/MRI, including precontrast and postcontrast standard spine MRI sequences. The image datasets were evaluated on dedicated workstations by 2 radiology residents and 1 board-certified nuclear medicine physician independently and then in consensus. Because of severe susceptibility artifacts, only 28 of 30 image datasets were evaluable, with a total of 29 regions of suspected spondylodiskitis. SUV ratios (affected disk/reference disk) were determined. The imaging results were compared with histopathology or clinical follow-up as a reference standard and subjected to statistical analysis.

RESULTS

The reference standards identified spondylodiskitis in 12 disks and excluded spondylodiskitis in 17 disks. For MRI alone, the sensitivity was 50%, the specificity was 71%, the positive predictive value was 54%, and the negative predictive value was 67%. Adding the PET data resulted in sensitivity, specificity, positive predictive value, and negative predictive value of 100%, 88%, 86%, and 100%, respectively. In a receiver operating characteristic curve analysis, an SUVmax ratio threshold of 2.1 resulted in 92% sensitivity and 88% specificity (area under the receiver operating characteristic curve, 0.95). Neither the level of C-reactive protein nor the leukocyte count at the time of PET/MRI was related to the reference standard diagnosis of spondylodiskitis.

CONCLUSION

In patients with inconclusive clinical or MRI findings, the use of (18)F-FDG PET/MRI significantly increased diagnostic certainty for the detection of spondylodiskitis.

Evaluation of Avulsion-Induced Neuropathology in Rat Spinal Cords with 18F-FDG Micro-PET/CT

Brachial plexus root avulsion (BPRA) leads to dramatic motoneuron death and glial reactions in the corresponding spinal segments at the late stage of injury. To protect spinal motoneurons, assessment of the affected spinal segments should be done at an earlier stage of the injury. In this study, we employed ¹⁸F-FDG small-animal PET/CT to assess the severity of BPRA-induced cervical spinal cord injuries. Adult Sprague-Dawley rats were randomly treated and divided into three groups: Av+NS (brachial plexus root avulsion (Av) treated with normal saline), Av+GM1 (treated with monosialoganglioside), and control. At time points of 3 day (d), 1 week (w), 2 w, 4 w and 8 w post-injury, ¹⁸F-FDG micro-PET/CT scans and neuropathology assessments of the injured spinal roots, as well as the spinal cord, were performed. The outcomes of the different treatments were compared. The results showed that BPRA induced local bleeding and typical Wallerian degeneration of the avulsed roots accompanied by ¹⁸F-FDG accumulations at the ipsilateral cervical intervertebral foramen. BPRA-induced astrocyte reactions and overexpression of neuronal nitric oxide synthase in the motoneurons correlated with higher ¹⁸F-FDG uptake in the ipsilateral cervical spinal cord during the first 2 w post-injury. The GM1 treatment reduced BPRA-induced astrocyte reactions and inhibited the de novo nNOS expressions in spinal motoneurons. The GM1 treatment also protected spinal motoneurons from avulsion within the first 4 w post-injury. The data from this study suggest that ¹⁸F-FDG PET/CT could be used to assess the severity of BPRA-induced primary and secondary injuries in the spinal cord. Furthermore, GM1 is an effective drug for reducing primary and secondary spinal cord injuries following BPRA.

NIR fluorescent small molecules for intraoperative imaging

Recent advances in bioimaging and nanomedicine have permitted the exploitation of molecular optical imaging in image-guided surgery; however, the parameters mediating optimum performance of contrast agents are not yet precisely determined. To develop ideal contrast agents for image-guided surgery, we need to consider the following criteria: (1) excitation and emission wavelengths in the near-infrared (NIR) window, (2) optimized optical characteristics for high in vivo performance, (3) overcoming or harnessing biodistribution and clearance, and (4) reducing nonspecific uptake. The design considerations should be focused on optimizing the optical and physicochemical property criteria. Biodistribution and clearance should first be considered because they mediate the fate of a contrast agent in the body such as how long after intravenous injection a contrast agent reaches the peak signal-to-background ratio (SBR) and how long the signal lasts (retention).