Avidin and 111In-labelled biotin scan: a new radioisotopic method for localising vascular graft infection

Tubercular pseudoaneurysm of the axillary artery

Tuberculous (TB) involvement of the vascular system has been reported in the preantibiotic era. We, hereby, report a case involving a teenage boy who presented to us with left upper limb pain followed by gradually progressive motor and sensory deficit over 1 month with preceding history of tuberculosis. Examination revealed a palpable, noncompressible, nonpulsatile swelling superior to the lateral third of the clavicle. Imaging through ultrasonography, computed tomography, and magnetic resonance imaging confirmed the presence of a pseudoaneurysm with compression of the underlying nerves. The child underwent surgical thrombectomy with pseudoaneurysm repair and arteriorrhaphy along with antitubercular medications with complete recovery at 6 months. The tissue staining, nucleic acid amplification tests, and histopathology confirmed TB etiology. Tuberculosis continues to remain a major health concern, especially in the developing world. High index of suspicion is necessary to diagnose such manifestations to avoid catastrophic sequelae.

Prosthetic vascular graft infection imaging

PURPOSE

We are reporting our experience with imaging of vascular graft infections using computed tomography angiography (CTA), white blood cell (WBC) scintigraphy and software-based fusion imaging.

MATERIAL AND METHODS

Institutional review board approval was obtained. We performed a retrospective review of patients who had clinical signs and symptoms of vascular graft infection in whom both WBC single photon emission computed tomography (SPECT) and CTA was performed between 2005 and 2010. We performed fusion imaging with available data using software coregistration technique and analyzed outcome of the patients.

RESULTS

We had 20 patients; 11 had grafts of the aorta, five had peripheral vascular grafts, three had aortic and peripheral vascular grafts, and one had a thoracic aortic graft. WBC imaging was positive in 10 patients, negative in six patients and indeterminate in 4 patients. CTA was positive in six patients, negative in four patients and indeterminate in 10 patients. Sensitivity, specificity, accuracy, positive predictive value and negative predictive value (NPV) for WBC, CTA and WBC SPECT/CTA fusion were 75/100/80/100/50%, 88/50/80/88/50% and 94/50/85/88/67% respectively.

CONCLUSION

The use of CTA, WBC scintigraphy, and image co-registration influenced the diagnostic confidence of graft infection and the outcome of the patients. Software-based fusion imaging of both modalities resulted in improved sensitivity, accuracy, and NPV.

111In-DTPA-Biotin uptake by Staphylococcus aureus

The potential of indium-111 labelled diethylenetriaminepentaacetic acid α,ω-bis(biocytinamide) (In-DTPA-Biotin) as a specific tracer in nuclear medicine imaging of vertebral osteomyelitis has been shown in a large series of consecutive patients. Biocytin is known to serve as a biotin source for a number of different microorganisms and quantitative studies on staphylococci indicated that on a molar basis biocytin seemed to have an activity equal to that of biotin. In this study, we evaluated the possibility of an illicit transport of In-DTPA-Biotin in cultures of Staphylococcus aureus on continued incubation for 24 h. Radiolabelled biocytin was prepared as described earlier and the stability and radiochemical purity was assessed in vitro for 24 h after labelling. Our data seem to demonstrate a passive transport of In-DTPA-Biotin into the cells of the microorganisms.

Diagnostics of "non-acute" vascular prosthesis infection using 18F-FDG PET/CT: our experience with 96 prostheses

INTRODUCTION

Vascular prosthesis infection (VPI) is a life-threatening complication that occurs in 0.5-5% of prostheses. Low-grade infections in non-acute patients are a diagnostic challenge requiring a new method with good diagnostic accuracy. The aim of this work was to define the accuracy of (18)F-FDG PET/CT in these settings and to identify essential parameters of the evaluation.

MATERIAL AND METHODS

PET/CT was performed prospectively in 76 consecutive patients with a total of 96 vascular prosthetic grafts in which infection was suspected. PET/CT scans were analysed in terms of the presence and intensity of focal and diffuse FDG uptake, the presence of an anastomotic pseudoaneurysm, the presence of an irregular boundary of infiltration, a combination of these, and the uptake ratio between the graft and blood background. The gold standard was based on operative/histopathological finding or a clinical follow up of >6 months.

RESULTS

Among the various assessed parameters only focal FDG uptake and an irregular graft boundary were significant predictors of VPI. Focal intense FDG uptake together with an irregular boundary of the lesion on CT scan predicted VPI with 97% probability, while smooth lesion boundaries and no focal FDG uptake predicted a probability of VPI of less than 5%. Even in lesions with nondiagnostic inhomogeneous focal FDG uptake (18/96) an irregular boundary effectively helped in decision-making with a probability of 28% (smooth) or 77% (irregular) for VPI.

CONCLUSION

PET/CT gave reliable results with an accuracy >95% in 75% of prostheses. PET/CT can identify those prostheses (25% of prosthesis) for which its diagnostic accuracy is diminished to 70-75%. In our series PET/CT was an excellent diagnostic modality for suspected VPI.

Endovascular treatment of a tuberculous infected aneurysm of the descending thoracic aorta: A word of caution

An infected aneurysm of the thoracic aorta due to mycobacterium tuberculosis is an unusual entity for which the classical treatment is antituberculosis chemotherapy and open-chest surgery. Recent improvements in endovascular treatments have led to their proposed use for infected aneurysms in patients for whom open surgery poses too high a risk. We report on a 68-year-old man with a tuberculous aortic aneurysm who had been treated with an endoprosthesis and antituberculosis chemotherapy. His clinical and radiological follow-up was uneventful and led to the discontinuation of pharmacological treatment after 16 months. However, a recurrence of the infection led to a fatal aortic rupture 4 months after discontinuation of therapy.

Clinical feasibility of two-step streptavidin/111In-biotin scintigraphy in patients with suspected vertebral osteomyelitis

PURPOSE

Streptavidin accumulates at sites of inflammation and infection as a result of increased capillary permeability. In addition to being utilised by bacteria for their own growth, biotin forms a stable, high-affinity non-covalent complex with avidin. The objective of this investigation was to determine the diagnostic performance of two-step streptavidin/111In-biotin imaging for evaluating patients with suspected vertebral osteomyelitis.

METHODS

We evaluated 55 consecutive patients with suspected vertebral osteomyelitis (34 women and 21 men aged 27-86 years), within 2 weeks after the onset of clinical symptoms. Thirty-two of the patients underwent magnetic resonance imaging (MRI) and 24, computed tomography (CT). DTPA-conjugated biotin was radiolabelled by incubating 500 microg of DTPA-biotin with 111 MBq of 111In-chloride. Two-step scintigraphy was performed by first infusing 3 mg streptavidin intravenously, followed 4 h later by 111In-biotin. Imaging was begun 60 min later.

RESULTS

Streptavidin/111In-biotin scintigraphy was positive in 32/34 patients with spinal infection (94.12% sensitivity). The study was negative in 19/21 patients without infection (95.24% specificity). The corresponding results for MRI and CT were 54.17% and 35.29% (sensitivity), and 75% and 57.14% (specificity), respectively. All statistical parameters of diagnostic performance (Youden's J index, kappa measure of agreement with correct classification, accuracy, sensitivity, specificity, positive likelihood and negative likelihood) were clearly better for streptavidin/111In-biotin scintigraphy than for either MRI or CT.

CONCLUSION

Streptavidin/111In-biotin scintigraphy is highly sensitive and specific for detecting vertebral osteomyelitis in the first 2 weeks after the onset of clinical symptoms, and is potentially very useful for guiding clinical decisions on instituting appropriate therapy.