Pitfalls in osteoarticular imaging: How to distinguish bone infection from tumour?

Imaging the Granzyme Mediated Host Immune Response to Viral and Bacterial Pathogens In Vivo Using Positron Emission Tomography

Understanding how the host immune system engages complex pathogens is essential to developing therapeutic strategies to overcome their virulence. While granzymes are well understood to trigger apoptosis in infected host cells or bacteria, less is known about how the immune system mobilizes individual granzyme species in vivo to combat diverse pathogens. Toward the goal of studying individual granzyme function directly in vivo, we previously developed a new class of radiopharmaceuticals termed "restricted interaction peptides (RIPs)" that detect biochemically active endoproteases using positron emission tomography (PET). In this study, we showed that secreted granzyme B proteolysis in response to diverse viral and bacterial pathogens could be imaged with [64Cu]Cu-GRIP B, a RIP that specifically targets granzyme B. Wild-type or germline granzyme B knockout mice were instilled intranasally with the A/PR/8/34 H1N1 influenza A strain to generate pneumonia, and granzyme B production within the lungs was measured using [64Cu]Cu-GRIP B PET/CT. Murine myositis models of acute bacterial (E. coli, P. aeruginosa, K. pneumoniae, and L. monocytogenes) infection were also developed and imaged using [64Cu]Cu-GRIP B. In all cases, the mice were studied in vivo using mPET/CT and ex vivo via tissue-harvesting, gamma counting, and immunohistochemistry. [64Cu]Cu-GRIP B uptake was significantly higher in the lungs of wild-type mice that received A/PR/8/34 H1N1 influenza A strain compared to mice that received sham or granzyme B knockout mice that received either treatment. In wild-type mice, [64Cu]Cu-GRIP B uptake was significantly higher in the infected triceps muscle versus normal muscle and the contralateral triceps inoculated with heat killed bacteria. In granzyme B knockout mice, [64Cu]Cu-GRIP B uptake above the background was not observed in the infected triceps muscle. Interestingly, live L. monocytogenes did not induce detectable granzyme B on PET, despite prior in vitro data, suggesting a role for granzyme B in suppressing their pathogenicity. In summary, these data show that the granzyme response elicited by diverse human pathogens can be imaged using PET. These results and data generated via additional RIPs specific for other granzyme proteases will allow for a deeper mechanistic study analysis of their complex in vivo biology.

Osteofibrous dysplasia-like adamantinoma of isolated fibula in a child mimicking chronic osteomyelitis with pathological fracture

The occurrence of a pathological fracture in children requires a rigorous diagnostic approach in order to establish the etiology and to develop a precise therapeutic strategy. Several causes are associated with these fractures, the most frequent being benign tumors in children in developed countries and chronic osteomyelitis in developing countries. More rarely, malignant tumors must however always be considered. The differential diagnosis on imaging may be difficult to establish between bone tumors and chronic infection. Surgical biopsy is therefore often performed to establish the precise origin of the fracture. We report the case of an adamantinoma (osteofibrous dysplasia-like) of the fibula in a 7-year-old child, discovered during the management of a pathologic fracture. The presumed diagnosis before biopsy was chronic osteomyelitis. A 14-cm-resection of the affected fibula was performed with good functional result. Differential diagnosis between adamantinoma, osteofibrous dysplasia and osteofibrous dysplasia-like adamantinoma remains very challenging.

Radiological changes in the formation of Brodie's abscess by sequential magnetic resonance imaging: a case report

Brodie's abscess is a relatively rare subacute form of osteomyelitis. Early diagnosis is challenging because of its insidious onset and vague symptoms. Magnetic resonance imaging is helpful in the diagnosis of Brodie's abscess; however, to date, no study has described the imaging findings of this disease in the early stage. Here, we present the case of a 14 year-old boy with Brodie's abscess in the proximal tibia. The lesion initially presented as a bone marrow edema in the proximal metaphysis of the left tibia on MRI and was misinterpreted as a bone bruise. Further radiological examination was performed 1 month later; this revealed the formation of an abscess cavity, which suggested Brodie's abscess. The patient was referred to our hospital and underwent curettage and debridement, which led to the definitive diagnosis of Brodie's abscess on histopathological findings and bacterial culture. On careful retrospective evaluation, the initial radiological findings suggested a microabscess on the metaphyseal side of the growth plate and bone marrow edema spreading from the lesion to the epiphysis. These radiological changes could be reliable evidence proving that the metaphyseal side of the growth plate is the origin of Brodie's abscess. Moreover, bone marrow edema with suspected microabscess in the metaphysis of the long bones can be the initial stage of the formation of Brodie's abscess and should be carefully followed up.

Acute osteoarticular infections in children are frequently forgotten multidiscipline emergencies: beyond the technical skills

Acute osteoarticular infections (AOI) should be treated as top emergencies. The first few days following the inception of infection are ultra-critical to long-term prognosis.A comprehensive road map for management of childhood AOI is still lacking despite recent advances in microbiology and imaging (magnetic resonance imaging). The many faces of childhood AOI warrant a multidiscipline approach to management.Laboratory and imaging findings of are still debatable and should not overshadow or delay a management plan based on the experienced physician's clinical judgment.Ample evidence-based practice supports the use of a few days of intravenous antibiotic administration followed by oral therapy until correlative clinical and basic laboratory (acute phase reactants) results improve.The growing body of evidence on 'high-risk' children/neonates of AOI warrants continual clinical extra-vigilance in identifying these patient subsets.Open drainage and debridement remain the mainstay of treatment of septic hips, whereas for other joints the use of alternative surgical techniques should be individualized or on case-by-case basis.Because the consequences of misdiagnosis of AOI are usually grave and permanent, proactive treatment/overtreatment is justified in the event of unconfirmed but suspicious diagnosis. Cite this article: EFORT Open Rev 2021;6:584-592. DOI: 10.1302/2058-5241.6.200155.

Longitudinal time-lapse in vivo micro-CT reveals differential patterns of peri-implant bone changes after subclinical bacterial infection in a rat model

Subclinical infection associated with orthopedic devices can be challenging to diagnose. The goal of this study was to evaluate longitudinal, microcomputed tomography (microCT) imaging in a rat model of subclinical orthopedic device-related infection caused by Staphylococcus epidermidis and four different Cutibacterium (previously Propionibacterium) acnes strains, and compare outcomes with non-inoculated and historical S. aureus-inoculated controls. Sterile screws or screws colonized with bacteria were placed in the tibia of 38 adult Wistar rats [n = 6 sterile screws; n = 6 S. epidermidis-colonized screws; n = 26 C. acnes-colonized screws (covering all three main subspecies)]. Regular microCT scans were taken over 28 days and processed for quantitative time-lapse imaging with dynamic histomorphometry. At euthanasia, tissues were processed for semiquantitative histopathology or quantitative bacteriology. All rats receiving sterile screws were culture-negative at euthanasia and displayed progressive bony encapsulation of the screw. All rats inoculated with S. epidermidis-colonized screws were culture-positive and displayed minor changes in peri-implant bone, characteristic of subclinical infection. Five of the 17 rats in the C. acnes inoculated group were culture positive at euthanasia and displayed bone changes at the interface of the screw and bone, but not deeper in the peri-implant bone. Dynamic histomorphometry revealed significant differences in osseointegration, bone remodeling and periosteal reactions between groups that were not measurable by visual observation of still microCT images. Our study illustrates the added value of merging 3D microCT data from subsequent timepoints and producing inherently richer 4D data for the detection and characterization of subclinical orthopedic infections, whilst also reducing animal use.

A Rare Case of Brodie's Abscess in HIV Patient Caused by Mycobacterium kansasii

We report a rare case of Brodie's abscess caused by Mycobacterium kansasii (M. kansasii). Our patient is a 39-year-old male who presented with right foot pain a month after a new diagnosis of HIV infection. X-ray and MRI were done, and the diagnosis of Brodie's abscess was confirmed. Surgical debridement was done, and bone cultures grew M. kansasii after five weeks. Brodie's abscess is a subacute form of osteomyelitis usually caused by Staphylococcus. Some other bacteria have been implicated in several case reports. To best of our knowledge, this is the first case of Brodie's abscess caused by M. kansasii. M. kansasii is the atypical mycobacteria causing infections in immunocompromised hosts as in HIV patients with low CD4 count. M. kansasii is usually associated with lung infections with rare extrapulmonary manifestations as in our case.

Distinguishing bone and soft tissue infections mimicking sarcomas requires multimodal multidisciplinary team assessment

INTRODUCTION

The aims of this study were to report the presenting characteristics and identify how best to distinguish bone and soft-tissue infections that mimic sarcomas.

MATERIALS AND METHODS

A total of 238 (211 osteomyelitis and 27 soft-tissue infections) patients referred to a tertiary sarcoma multidisciplinary team with suspected sarcoma who were ultimately diagnosed with a bone or soft tissue infection were included. Data from a prospectively collated database was analysed retrospectively.

RESULTS

Of all possible bone and soft-tissue sarcoma referrals, a diagnosis of infection was made in 2.1% and 0.7%, respectively. Median age was 18 years in the osteomyelitis group and 46 years in the soft-tissue infection group. In the osteomyelitis group, the most common presenting features were pain (85.8%) and swelling (32.7%). In the soft-tissue infection group, the most common clinical features were swelling (96.3%) and pain (70.4%). Those in the soft-tissue group were more likely to have raised inflammatory markers. Radiological investigations were unable to discern between tumour or infection in 59.7% of osteomyelitis and 81.5% of soft-tissue infection cases. No organism was identified in 64.9% of those who had a percutaneous biopsy culture.

CONCLUSIONS

This study has highlighted that infection is frequently clinically indistinguishable from sarcoma and remains a principle non-neoplastic differential diagnosis. When patients are investigated for suspected sarcoma, infections can be missed due to falsely negative radiological investigations and percutaneous biopsy. As no single clinical, biochemical or radiological feature or investigation can be relied upon for diagnosis, clinicians should have a low threshold for tissue biopsy and discussion in a sarcoma multidisciplinary team meeting.

A practical guide for planning pelvic bone percutaneous interventions (biopsy, tumour ablation and cementoplasty)

Percutaneous approaches for pelvic bone procedures (bone biopsies, tumour ablation and cementoplasty) are multiple and less well systematised than for the spine or extremities. Among the different imaging techniques that can be used for guidance, computed tomography (CT) scan is the modality of choice because of the complex pelvic anatomy. In specific cases, such as cementoplasty where real-time evaluation is a determinant, a combination of CT and fluoroscopy is highly recommended. The objective of this article is to propose a systematic approach for image-guided pelvic bone procedures, as well as to provide some technical tips. We illustrate the article with multiple examples, and diagrams of the approaches and important structures to avoid to perform these procedures safely.

TEACHING POINTS

• Pelvic bone procedures are safe to perform if anatomical landmarks are recognised. • The safest approach varies depending on the pelvic level. • CT is the modality of choice for guiding pelvic percutaneous procedures. • Fluoroscopy is recommended when real-time monitoring is mandatory. • MRI can also be used for guiding pelvic percutaneous procedures.

Quantitative and qualitative analysis of bone flap resorption in patients undergoing cranioplasty after decompressive craniectomy

OBJECTIVE

Autologous bone cranioplasty after decompressive craniectomy entails a notable burden of difficult postoperative complications, such as infection and bone flap resorption (BFR), leading to mechanical failure. The prevalence and significance of asymptomatic BFR is currently unclear. The aim of this study was to radiologically monitor the long-term bone flap survival and bone quality change in patients undergoing autologous cranioplasty.

METHODS

The authors identified all 45 patients who underwent autologous cranioplasty at Oulu University Hospital, Finland, between January 2004 and December 2014. Using perioperative and follow-up CT scans, the volumes and radiodensities of the intact bone flap prior to surgery and at follow-up were calculated. Relative changes in bone flap volume and radiodensity were then determined to assess cranioplasty survival. Sufficient CT scans were obtainable from 41 (91.1%) of the 45 patients.

RESULTS

The 41 patients were followed up for a median duration of 3.79 years (25th and 75th percentiles = 1.55 and 6.66). Thirty-seven (90.2%) of the 41 patients had some degree of BFR and 13 (31.7%) had a remaining bone flap volume of less than 80%. Patients younger than 30 years of age had a mean decrease of 15.8% in bone flap volume compared with the rest of the cohort. Bone flap volume was not found to decrease linearly with the passing of time, however. The effects of lifestyle factors and comorbidities on BFR were nonsignificant.

CONCLUSIONS

In this study BFR was a very common phenomenon, occurring at least to some degree in 90% of the patients. Decreases in bone volume were especially prominent in patients younger than 30 years of age. Because the progression of resorption during follow-up was nonlinear, routine follow-up CT scans appear unnecessary in monitoring the progression of BFR; instead, clinical follow-up with mechanical stability assessment is advised. Partial resorption is most likely a normal physiological phenomenon during the bone revitalization process.

A Brodie’s abscess with soft tissue collection—complicating an already difficult diagnosis

A healthy 14-year-old boy with a 3-month history of thigh pain and swelling is referred to a specialist centre with an uncertain diagnosis. After extensive tests and imaging a Brodie’s abscess is diagnosed. The abscess is complicated by a fistula (cloaca) through the cortical bone of the femur, resulting in a large complex soft tissue collection. This is a presentation, we are unaware has been documented in any literature. After specialist multi-team combined management (Paediatric Trauma and Orthopaedic and Paediatric Infectious Diseases), the patient undergoes two surgical procedures, and extensive antibiotic cover. The patient makes a good recovery with no long lasting sequelae to date.

Diagnostic value of 99mTc-ubiquicidin scintigraphy in differentiation between osteomyelitis and bone tumors

AIM

The differentiation of osteomyelitis from bone tumors is of great importance in clinical decision-making; however, the features of both osteomyelitis and bone tumors are noncontributory. Tc-ubiquicidin scintigraphy is a new promising method with the ability to specifically localize the infection site by bacterial cell membrane binding. This study aimed to evaluate the ability of this radiopeptide for the differentiation of these two entities.

PATIENTS AND METHODS

Thirty consecutive patients (mean age=20.9 years) suspected of having either osteomyelitis or bone tumor were included in this prospective study. A Tc-UBI scan was performed in both dynamic and static phases and the images were assessed qualitatively and semiquantitatively. The final diagnosis was established for 29 patients on the basis of surgical findings and microbiological and pathology assessments as well as any other clinical, laboratory, or imaging findings during patient follow-up.

RESULTS

The final diagnosis was infectious and noninfectious processes in 19 and 10 patients, respectively. Visual assessment could not distinguish between osteomyelitis and bone tumors. However, the time-activity pattern of the images proved to be promising. The sensitivity, specificity, negative and positive predictive value, and accuracy of the time-activity curve for osteomyelitis were 73.6 (54-93), 100, 66.6 (43-91), 100, and 82%, respectively. The mean±SD tumor/nontumor (T/NT) ratios for 30 min images were 2.22±0.45 and 2.02±0.51 for infectious and noninfectious processes, respectively (P=0.29). Using a cutoff value of 0.97 for the T/NT ratio, the sensitivity and specificity were calculated to be 78.9 and 50%, respectively.

CONCLUSION

Although Tc-UBI scintigraphy in the dynamic imaging format was very useful with high accuracy in differentiating between infectious and tumoral lesions, it was not useful to distinguish these two entities on the basis of visual assessment or T/NT ratio measurement on static images. The study also showed the high accuracy of this noninvasive modality in acute osteomyelitis with low diagnostic value in chronic infectious processes.

Benign Bone Conditions That May Be FDG-avid and Mimic Malignancy

Positron emission tomography with the radiotracer ¹⁸F-fluoro-2-deoxy-d-glucose (FDG) plays an important role in the evaluation of bone pathology. However, FDG is not a cancer-specific agent, and knowledge of the differential diagnosis of benign FDG-avid bone alterations that may resemble malignancy is important for correct patient management, including the avoidance of unnecessary additional invasive tests such as bone biopsy. This review summarizes and illustrates the spectrum of benign bone conditions that may be FDG-avid and mimic malignancy, including osteomyelitis, bone lesions due to benign systemic diseases (Brown tumor, Erdheim-Chester disease, Gaucher disease, gout and other types of arthritis, Langerhans cell histiocytosis, and sarcoidosis), benign primary bone lesions (bone cysts, chondroblastoma, chondromyxoid fibroma, desmoplastic fibroma, enchondroma, giant cell tumor and granuloma, hemangioma, nonossifying fibroma, and osteoid osteoma and osteoblastoma), and a group of miscellaneous benign bone conditions (post bone marrow biopsy or harvest status, bone marrow hyperplasia, fibrous dysplasia, fractures, osteonecrosis, Paget disease of bone, particle disease, and Schmorl nodes). Several ancillary clinical and imaging findings may be helpful in discriminating benign from malignant FDG-avid bone lesions. However, this distinction is sometimes difficult or even impossible, and tissue acquisition will be required to establish the final diagnosis.

Epidemiology and Management of Acute, Uncomplicated Septic Arthritis and Osteomyelitis: Spanish Multicenter Study

BACKGROUND

Acute osteoarticular infection (OAI) is a potentially severe disease. The aim of this study was to evaluate the etiology, clinical characteristics and therapeutic approach of OAI in children in Spain.

METHODS

Medical records from children <14 years with OAI from 25 hospitals between 2008 and 2012 were reviewed. Confirmed osteomyelitis (OM) and septic arthritis (SA) required a positive bacterial isolate; otherwise, they were considered probable. Probable SA with <40,000 cells/mm in joint fluid was not included.

RESULTS

A total of 641 children were evaluated. Two hundred and ninety-nine cases (46%) were OM, 232 (36%) SA, 77 (12%) osteoarthritis and 33 (5%) spondylodiscitis. Children with OM were older (63 vs. 43 months for SA; P < 0.001). Magnetic resonance imaging and bone scintigraphy had the highest yield for OM diagnosis (94%). Arthrocentesis was performed in 96% of SA. A microorganism was isolated in 246 patients (38%: 33% OM vs. 55% SA; P < 0.001): Staphylococcus aureus was the most common (63%), followed by Kingella kingae (15%) and Streptococcus pyogenes (9%). Ninety-five percent of children initially received IV antibiotics, mostly cefotaxime + cloxacillin (60%) or cloxacillin (40%). Total treatment duration was 38 (±31) days for OM and 28 (±16) days for SA (P < 0.0001). Twenty percent of children with OM (46% because of complications) and 53% with SA (95% initial arthrotomy) underwent surgery. Patients with SA were compared according to initial arthrotomy (n = 123) versus arthrocentesis (n = 109), and no clinical differences were observed, except for higher rate of hip SA in the former (50% vs. 9%; P < 0.001). Children with arthrocentesis had less sequelae [6.6% vs. 1%; P = 0.03, odds ratio = 0.58 (95% confidence interval: 0.45-0.76)], but not in the multivariate analysis.

CONCLUSIONS

This is the largest pediatric cohort of OAI in Spain. S. aureus was the most common isolate, although K. kingae was recovered in a high proportion of cases. Conservative management was applied in half of the patients. There was a low rate of sequelae, even with nonsurgical approaches.

Intramedullary fat globules related to bone trauma: a new MR imaging finding

OBJECTIVE

The purpose of this study is to describe intraosseous fat globules related to bone trauma that are detectable with magnetic resonance imaging (MRI), to define the relationship of this finding to fracture and bone contusion, to establish the frequency and associated findings. A proposed pathogenesis is presented.

MATERIALS AND METHODS

We retrospectively reviewed 419 knee MRI examinations in patients with a history of recent injury and MRI findings of fracture or bone contusion. As a control population, 268 knee MRI examinations in patients without MRI findings of recent bone injury were also reviewed.

RESULTS

Eight of 419 (1.9%) patients with acute or subacute knee injury with positive findings of osseous trauma on MRI demonstrated intraosseous fat globules. The mean age of patients with fat globules was greater than that of those without fat globules, and the finding was more commonly seen in women. Fat globules were hyperintense to the normal fatty marrow present elsewhere in the bone on TI-weighted imaging and had a surrounding halo of high signal intensity on fluid-sensitive imaging.

CONCLUSIONS

Intramedullary fat globules related to bone injury visible on MRI are thought to be due to coalesced fat released by the necrosis of fatty marrow cells. The pathogenesis is supported by histologic studies of fat globules related to osteomyelitis, bone contusions and fractures. As the medullary cavity of long bones in older patients contains more fat than hematopoetic bone marrow, it is likely that this finding is more common with advancing age.