Imaging Psoas Sign in Lumbar Spinal Infections: Evaluation of Diagnostic Accuracy and Comparison with Established Imaging Characteristics

Imaging assessment of spine infection

This article comprehensively reviews current imaging concepts in spinal infection with primary focus on infectious spondylodiscitis (IS) as well as the less common entity of facet joint septic arthritis (FSA). This review encompasses the multimodality imaging appearances (radiographs, CT, MRI, and nuclear imaging) of spinal infection-both at initial presentation and during treatment-to aid the radiologist in guiding diagnosis and successful management. We discuss the pathophysiology of spinal infection in various patient populations (including the non-instrumented and postoperative spine) as well as the role of imaging-guided biopsy. We also highlight several non-infectious entities that can mimic IS (both clinically and radiologically) that should be considered during image interpretation to avoid misdiagnosis. These potential mimics include the following: Modic type 1 degenerative changes, acute Schmorl's node, neuropathic spondyloarthropathy, radiation osteitis, and inflammatory spondyloarthropathy (SAPHO syndrome).

Value of [18F]FDG PET/CT in Diagnosis and Management of Spondylodiscitis

Vertebral osteomyelitis is the third most common form of osteomyelitis in patients over 50 years of age.Whereas prompt (pathogen-directed) therapy is crucially associated with better outcomes, the heterogeneous clinical presentation of disease with unspecific symptoms often delays adequate treatment initiation. Diagnosis requires a careful investigation of medical history, clinical findings and diagnostic imaging, including magnetic resonance imaging and nuclear medicine techniques.Due to its high sensitivity, [18F]FDG PET/CT is becoming increasingly important in diagnosis and management of spondylodiscitis, especially in the postoperative setting with presence of spinal hardware or other implantable devices in which MRI is limited.

Understanding a mass in the paraspinal region: an anatomical approach

The paraspinal region encompasses all tissues around the spine. The regional anatomy is complex and includes the paraspinal muscles, spinal nerves, sympathetic chains, Batson's venous plexus and a rich arterial network. A wide variety of pathologies can occur in the paraspinal region, originating either from paraspinal soft tissues or the vertebral column. The most common paraspinal benign neoplasms include lipomas, fibroblastic tumours and benign peripheral nerve sheath tumours. Tumour-like masses such as haematomas, extramedullary haematopoiesis or abscesses should be considered in patients with suggestive medical histories. Malignant neoplasms are less frequent than benign processes and include liposarcomas and undifferentiated sarcomas. Secondary and primary spinal tumours may present as midline expansile soft tissue masses invading the adjacent paraspinal region. Knowledge of the anatomy of the paraspinal region is of major importance since it allows understanding of the complex locoregional tumour spread that can occur via many adipose corridors, haematogenous pathways and direct contact. Paraspinal tumours can extend into other anatomical regions, such as the retroperitoneum, pleura, posterior mediastinum, intercostal space or extradural neural axis compartment. Imaging plays a crucial role in formulating a hypothesis regarding the aetiology of the mass and tumour staging, which informs preoperative planning. Understanding the complex relationship between the different elements and the imaging features of common paraspinal masses is fundamental to achieving a correct diagnosis and adequate patient management. This review gives an overview of the anatomy of the paraspinal region and describes imaging features of the main tumours and tumour-like lesions that occur in the region.

Value of [18F]FDG PET/CT in diagnosis and management of spondylodiscitis

Vertebral osteomyelitis is the third most common form of osteomyelitis in patients over 50 years of age.Whereas prompt (pathogen-directed) therapy is crucially associated with better outcomes, the heterogeneous clinical presentation of disease with unspecific symptoms often delays adequate treatment initiation. Diagnosis requires a careful investigation of medical history, clinical findings and diagnostic imaging, including magnetic resonance imaging and nuclear medicine techniques.Due to its high sensitivity, [¹⁸F]FDG PET/CT is becoming increasingly important in diagnosis and management of spondylodiscitis, especially in the postoperative setting with presence of spinal hardware or other implantable devices in which MRI is limited.

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.

The value of magnetic resonance imaging and computed tomography in the study of spinal disorders

Computed tomography (CT) and magnetic resonance imaging (MRI) have replaced conventional radiography in the study of many spinal conditions, it is essential to know when these techniques are indicated instead of or as complementary tests to radiography, which findings can be expected in different clinical settings, and their significance in the diagnosis of different spinal conditions. Proper use of CT and MRI in spinal disorders may facilitate diagnosis and management of spinal conditions. An adequate clinical approach, a good understanding of the pathological manifestations demonstrated by these imaging techniques and a comprehensive report based on a universally accepted nomenclature represent the indispensable tools to improve the diagnostic approach and the decision-making process in patients with spinal pain. Several guidelines are available to assist clinicians in ordering appropriate imaging techniques to achieve an accurate diagnosis and to ensure appropriate medical care that meets the efficacy and safety needs of patients. This article reviews the clinical indications of CT and MRI in different pathologic conditions affecting the spine, including congenital, traumatic, degenerative, inflammatory, infectious and tumor disorders, as well as their main imaging features. It is intended to be a pictorial guide to clinicians involved in the diagnosis and treatment of spinal disorders.

ACR Appropriateness Criteria® Suspected Spine Infection

Spine infection is both a clinical and diagnostic imaging challenge due to its relatively indolent and nonspecific clinical presentation. The diagnosis of spine infection is based upon a combination of clinical suspicion, imaging evaluation and, when possible, microbiologic confirmation performed from blood cultures or image-guided percutaneous or open spine biopsy. With respect to the imaging evaluation of suspected spine infection, MRI without and with contrast of the affected spine segment is the initial diagnostic test of choice. As noncontrast MRI of the spine is often used in the evaluation of back or neck pain not responding to conservative medical management, it may show findings that are suggestive of infection, hence this procedure may also be considered in the evaluation of suspected spine infection. Nuclear medicine studies, including skeletal scintigraphy, gallium scan, and FDG-PET/CT, may be helpful in equivocal or select cases. Similarly, radiography and CT may be appropriate for assessing overall spinal stability, spine alignment, osseous integrity and, when present, the status of spine instrumentation or spine implants. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Clinicoradiographic predictors of percutaneous bone biopsy results among patients with suspected thoracolumbar spine infection

BACKGROUND

Image-guided percutaneous thoracolumbar spine biopsy is frequently performed in the setting of suspected septic facet arthritis or discitis osteomyelitis (DOM). There are limited data regarding factors associated with a positive biopsy result among these patients.

MATERIALS AND METHODS

Patients with suspected DOM who underwent spine biopsy were identified. Samples yielding a positive culture and/or histopathology suggestive of acute osteomyelitis were considered positive. The associations between selected medical comorbidities, laboratory values, pre-biopsy antibiotic administration, imaging findings and biopsy results were investigated.

RESULTS

121 patients underwent percutaneous biopsy with 35.5% yielding positive results. Biopsy results showed no correlation with comorbidities. The only laboratory value that correlated with a positive biopsy yield was blood culture positivity (p = 0.03). The imaging findings that correlated with a positive biopsy yield were the presence of a paraspinal fluid collection or epidural abscess (p = 0.003 and 0.018, respectively). Sampling paraspinal fluid collections, when present, resulted in a higher rate of a positive biopsy yield compared to sampling of bone or disc (p = 0.006). Patients who received antibiotics had a higher rate of a positive biopsy yield (p = 0.014). In those with positive blood cultures, biopsy yielded the same antimicrobial susceptibility profile in 13/14 cases.

CONCLUSION

The presence of a paraspinal fluid collection or epidural abscess is correlated with positive biopsy yield, and paraspinal fluid collections should be targeted for biopsy. Other imaging findings did not correlate with biopsy yield. Biopsy may not offer additional information for patients with positive blood cultures.

A Clinical Prediction Tool for MRI in Emergency Department Patients with Spinal Infection

Introduction

Patients with pyogenic spinal Infection (PSI) are often not diagnosed at their initial presentation, and diagnostic delay is associated with increased morbidity and medical-legal risk. We derived a decision tool to estimate the risk of spinal infection and inform magnetic resonance imaging (MRI) decisions.

Methods

We conducted a two-part prospective observational cohort study that collected variables from spine pain patients over a six-year derivation phase. We fit a multivariable regression model with logistic coefficients rounded to the nearest integer and used them for variable weighting in the final risk score. This score, SIRCH (spine infection risk calculation heuristic), uses four clinical variables to predict PSI. We calculated the statistical performance, MRI utilization, and model fit in the derivation phase. In the second phase we used the same protocol but enrolled only confirmed cases of spinal infection to assess the sensitivity of our prediction tool.

Results

In the derivation phase, we evaluated 134 non-PSI and 40 PSI patients; median age in years was 55.5 (interquartile range [IQR] 38–70 and 51.5 (42–59), respectively. We identified four predictors for our risk score: historical risk factors; fever; progressive neurological deficit; and C-reactive protein (CRP) ≥ 50 milligrams per liter (mg/L). At a threshold SIRCH score of ≥ 3, the predictive model’s sensitivity, specificity, and positive predictive value were, respectively, as follows: 100% (95% confidence interval [CI], 100–100%); 56% (95% CI, 48–64%), and 40% (95% CI, 36–46%). The area under the receiver operator curve was 0.877 (95% CI, 0.829–0.925). The SIRCH score at a threshold of ≥ 3 would prompt significantly fewer MRIs compared to using an elevated CRP (only 99/174 MRIs compared to 144/174 MRIs, P <0.001). In the second phase (49 patient disease-only cohort), the sensitivities of the SIRCH score and CRP use (laboratory standard cut-off 3.5 mg/L) were 92% (95% CI, 84–98%), and 98% (95% CI, 94–100%), respectively.

Conclusion

The SIRCH score provides a sensitive estimate of spinal infection risk and prompts fewer MRIs than elevated CRP (cut-off 3.5 mg/L) or clinician suspicion.

Spine MRI: A Review of Commonly Encountered Emergent Conditions

Over the last 2 decades, the proliferation of magnetic resonance imaging (MRI) availability and continuous improvements in acquisition speeds have led to significantly increased MRI utilization across the health care system, and MRI studies are increasingly ordered in the emergent setting. Depending on the clinical presentation, MRI can yield vital diagnostic information not detectable with other imaging modalities. The aim of this text is to report on the up-to-date indications for MRI of the spine in the ED, and review the various MRI appearances of commonly encountered acute spine pathology, including traumatic injuries, acute non traumatic myelopathy, infection, neoplasia, degenerative disc disease, and postoperative complications. Imaging review will focus on the aspects of the disease process that are not readily resolved with other modalities.

The needle and the damage done: musculoskeletal and vascular complications associated with injected drug use

Injected drug use is associated with a wide range of medical complications which are predominantly musculoskeletal and vascular in nature. Illicit drug use is increasing worldwide. Patients with complications of injected drug use often present in a non-specific manner without a reliable clinical history. Musculoskeletal complications are typically infective in aetiology and may vary widely in severity from mild to life-threatening. A multimodal imaging approach is often required for both diagnostic imaging and image-guided sampling. Plain radiographs are often an important initial test, for example in identifying retained needles from injection. Ultrasound and CT play important roles in the assessment of complex soft tissue complications and MRI is the imaging modality of choice for bone and joint disorders. Vascular complications may be venous or arterial in nature and usually occur locally at the injection site. These complications may be related to direct injury to the vessel wall by a needle, or secondary to local infection and inflammation. A multimodal imaging strategy is also often required in the assessment of these vascular complications, typically involving a combination of ultrasound and CT. Familiarity with the multimodal imaging features of the complications related to injected drug use is crucially important as they may be rapidly progressive and life-threatening and require timely diagnosis.

Diagnostic and interventional management of infective spine diseases

Spondylodiscitis (SD) is one of the main causes of back pain. Although the low mortality, high morbidity is related to spondilodiscitys, leading spine instability, chronic pain or neurological deficit. Diagnostic imaging plays a primary role in diagnosing spondylodiscitis. However different accuracy is highlighted by different diagnostic tool, depending also on timing of disease which represents a cardinal element for the phenotypic manifestation of the disease, beyond spatial resolution and tissue characterization proper of specific modality imaging. Conventional Radiology (CR), Computed Tomography (CT) and MRI (Magnetic Resonance Imaging) all have proven to be of primary importance in the approach to spondylodiscitis, although magnetic resonance imaging has demonstrated the greatest advantage in identifying the disease from its earliest stages, demonstrating high sensitivity and specificity (92% and 96%, respectively). This review focus on the role of different imaging modality in the approach to the spondylodiscitis, also addressing the role of interventional radiology that is pivotal not only for a diagnosis of certainty through biopsy, but also for a minimally-invasive treatment of paravertebral abscesses spondylodiscitis-related. (www.actabiomedica.it)

Vertebral Bone Marrow and Endplate Assessment on MR Imaging for the Differentiation of Modic Type 1 Endplate Changes and Infectious Spondylodiscitis

On magnetic resonance (MR) imaging, Modic type 1 (MT1) endplate changes and infectious spondylodiscitis share similar findings. Therefore, this study investigated vertebral bone marrow and endplate changes to enable their differentiation. The lumbar spine MR examinations of 91 adult patients were retrospectively included: 39 with MT1; 19 with early spondylodiscitis without abscess; and 33 with advanced spondylodiscitis with abscess. The assessment included percentage of bone marrow edema on sagittal short tau inversion recovery images, and the signal ratio of edema to unaffected bone and endplate contour (normal; irregular, yet intact; blurred; destructive) on sagittal unenhanced T1-weighted images. Differences were tested for statistical significance by Chi-square test and mixed model analysis of variance. The MR diagnostic accuracy in differentiating MT1 and spondylodiscitis was assessed by cross-tabulation and receiver-operating characteristic analysis. The endplate contours, edema extents, and T1-signal ratios of MT1 (extent, 31.96%; ratio, 0.83) were significantly different (p < 0.001) from early spondylodiscitis (56.42%; 0.60), and advanced spondylodiscitis (91.84%; 0.61). The highest diagnostic accuracy (sensitivity, 94.87%; specificity, 94.23%; accuracy, 94.51%) in identifying MT1 was provided by an irregular, yet intact endplate contour. This may be a useful MR feature for the differentiation between MT1 and spondylodiscitis, particularly in its early stage.

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.

Imaging of Acute Low Back Pain

Acute low back pain, defined as less than 6 weeks in duration, does not require imaging in the absence of "red flags" that may indicate a cause, such as fracture, infection, or malignancy. When imaging is indicated, it is important to rule out a host of abnormalities that may be responsible for the pain and any associated symptoms. A common mnemonic VINDICATE can help ensure a thorough consideration of the possible causes.

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.

Magnetic resonance imaging of bacterial and tuberculous spondylodiscitis with associated complications and non-infectious spinal pathology mimicking infections: a pictorial review

Magnetic resonance (MR) imaging plays an important role in the evaluation of bacterial and tuberculous spondylodiscitis and associated complications. Owing to its high sensitivity and specificity, it is a powerful diagnostic tool in the early diagnosis of ongoing infections, and thus provides help in prompt initiation of appropriate, therapy which may be medical or surgical, by defining the extent of involvement and detection of complications such as epidural and paraspinal abscesses. More specifically, MR imaging helps in differentiating bacterial from tuberculous infections and enables follow up of progression or resolution after appropriate treatment. However, other non-infectious pathology can demonstrate similar MR imaging appearances and one should be aware of these potential mimickers when interpreting MR images. Radiologists and other clinicians need to be aware of these potential mimics, which include such pathologies as Modic type I degenerative changes, trauma, metastatic disease and amyloidosis. In this pictorial review, we will describe and illustrate imaging findings of bacterial and tuberculous spondylodiscitis, their complications and non-infectious pathologies that mimic these spinal infections.

Infections of the Spine

Pyogenic infections of the bony spinal column and the intervertebral discs are on a steady rise in an aging western population. Despite advanced medical imaging, this clinical entity of devastating consequences if missed, still presents a diagnostic conundrum and is plagued by an unacceptably long diagnostic delay. The aim of this article is to raise awareness of the heterogeneity of spinal infections paralleling the complex structure of the spinal column and neighboring soft tissues. Emphasis is placed on the clinical presentation and management of septic facet joints and psoas muscle abscesses associated with lumbar spondylodiscitis.