Nuclear Medicine Imaging of Vascular Prosthesis Infections

Abstract

Vascular prosthesis infection is a devastating complication of vascular reconstructive surgery. Although the use of antibiotics has reduced its incidence, this complication must always be taken into consideration, since infection can occur years after implantation. Infections can be divided into early onset or late onset, depending on the time they occur after vascular surgery. It is crucial to promptly identify and treat the infection, due to high morbidity and mortality associated with this condition. Several imaging modalities are currently available for the diagnosis of vascular graft infection; among these, nuclear medicine imaging offers not only early and accurate detection but also an evaluation of treatment response.

Clinical Cases

6.1.1 Case 6.1

6.1.1.1 Background

A 61-year-old patient with aorto-bisiliac prosthesis implanted 6 years before and recent development of fever. CT angiography performed 2 months previously revealed only a slight iodinated contrast endoleak without sign of infection in the prosthesis. In the same period, a blood test showed high level of ESR, C-reactive protein, and leukocytes count.

Scintigraphy with ^99mTc-HMPAO-WBC was performed 5 min (early acquisition, Fig. 6.1a) and 1 h (late acquisition, Fig. 6.1b) post-injection. The late acquisition showed abnormal WBC accumulation in the common right iliac artery (arrow). CT angiography (Fig. 6.1c) did not reveal any morphologic abnormality, while the fused SPECT/CT image (Fig. 6.1d) confirmed the localization of WBC hyperaccumulation in the distal portion of the right iliac component of the vascular prosthesis (arrow).

Fig. 6.1

See text

6.1.1.2 Suspected Site of Disease

Aorto-bisiliac vascular prosthesis.

6.1.1.3 Radiopharmaceutical Activity

^99mTc-HMPAO-WBC, 540 MBq.

6.1.1.4 Imaging

Planar acquisitions at 5 min and 1 h after administration of the radiolabeled leukocytes. SPECT/CT imaging acquired immediately after acquisition of the 1-h planar image.

6.1.1.5 Conclusion/Teaching Points

A patient with strong clinical suspicion of infection but negative CT angiography should undergo a ^99mTc-HMPAO-WBC scintigraphy to exclude or confirm with certainty infection of the vascular prosthesis.

6.1.2 Case 6.2

6.1.2.1 Background

A 69-year-old patient with endovascular aorto-bisiliac prosthesis, recent onset of fever, and increased serum levels of ESR, C-reactive protein, and leukocytes count.

Scintigraphy with ^99mTc-HMPAO-WBC was acquired 5-min (early acquisition, Fig. 6.2a) and 1 h (late acquisition, Fig. 6.2b, c). Anterior and right anterior oblique views of late acquisition (Fig. 6.2b, c) showed a focus of pathologic accumulation of WBC in the median abdominal region (arrow). CT angiography (Fig. 6.2d) revealed a peri-aortic abscess collection medially to the psoas muscle (arrowhead). The fused SPECT/CT fused image (Fig. 6.2e) localized the focus of WBC hyperaccumulation in the aortic component of the vascular prosthesis (arrow).

Fig. 6.2

See text

6.1.2.2 Suspected Site of Disease

Endovascular aorto-bisiliac prosthesis.

6.1.2.3 Radiopharmaceutical Activity

^99mTc-HMPAO-WBC, 540 MBq.

6.1.2.4 Imaging

Planar acquisitions at 5 min and 1 h after administration of the radiolabeled leukocytes. SPECT/CT imaging acquired immediately after acquisition of the 1-h planar image.

6.1.2.5 Conclusion/Teaching Points

The use of hybrid imaging SPECT/CT offers great help not only in detecting the presence of infectious foci but also in localizing precisely the anatomical site of infection.

6.1.3 Case 6.3

6.1.3.1 Background

A 59-year-old patient with endovascular aorto-bisiliac prosthesis implanted 1 year earlier. CT angiography performed 1 month previously showed confluent corpuscular fluid collections with air bubbles adjacent to the endoprosthesis throughout its entire course. The most bulky collection was located on the left side expanding in part in the psoas muscle and adjacent to L4.

Scintigraphy with ^99mTc-HMPAO-WBC was performed 5 min (early acquisition, Fig. 6.3a) and 1 h post-injection (late acquisition, Fig. 6.3b, c). The planar anterior and right anterior-oblique late views showed a focal accumulation of labeled leukocytes (arrow) in the vascular prosthesis (dashed red line) adjacent to the left edge of the lumbar column. The fused SPECT/CT image (Fig. 6.3d) localized WBC hyperaccumulation in the aortic component of the vascular prosthesis (arrow).

Fig. 6.3

See text

6.1.3.2 Suspected Site of Disease

Aorto-bisiliac vascular prosthesis.

6.1.3.3 Radiopharmaceutical Activity

^99mTc-HMPAO-WBC, 550 MBq.

6.1.3.4 Imaging

Planar acquisitions at 5 min and 1 h after administration of the radiolabeled leukocytes. SPECT/CT imaging acquired immediately after acquisition of the 1-h planar image.

6.1.3.5 Conclusion/Teaching Points

The use of hybrid SPECT/CT imaging is crucial for identifying exact anatomical location of the infection.

6.1.4 Case 6.4

6.1.4.1 Background

A 71-year-old patient with aorto-bifemoral by-pass implanted 4 years earlier. The patient was admitted to the hospital after the recent onset of fever and appearance of a lump located in the left groin. A CT angiography scan revealed a corpuscular fluid collection adjacent to the left distal vascular prosthesis. This collection reached the left iliac fossa and superficially the left groin.

Scintigraphy with ^99mTc-HMPAO-WBC was performed 5 min (early acquisition, Fig. 6.4a) and 1 h (late acquisition, Fig. 6.4b, c) post-injection. The planar anterior early acquisition showed faint accumulation of labeled leukocytes (arrowhead). The anterior and left anterior oblique late views (Fig. 6.4b, c) showed a more definite focus of abnormally increased accumulation of labeled WBC in the left iliac fossa and in the ipsilateral groin region (arrows). The fused SPECT/CT image (Fig. 6.4d) localized WBC hyperaccumulation along the left branch and the distal anastomosis of the aorto-bifemoral bypass previously implanted (arrows).

Fig. 6.4

See text

6.1.4.2 Suspected Site of Disease

Aorto-bifemoral bypass.

6.1.4.3 Radiopharmaceutical Activity

^99mTc-HMPAO-WBC, 535 MBq.

6.1.4.4 Imaging

Planar acquisitions at 5 min and 1 h after administration of the radiolabeled leukocytes. SPECT/CT imaging acquired immediately after acquisition of the 1-h planar image.

6.1.4.5 Conclusion/Teaching Points

The use of hybrid imaging CT/SPECT is crucial for identifying exact anatomical location of the infection.

6.1.5 Case 6.5

6.1.5.1 Background

A 51-year-old patient with rheumatic fever and secondary annulo-aortic ectasia treated with aortic composite valve graft about 18 months earlier. Approximately 1 year later, the patient was treated for an episode of endocarditis caused by Enterococcus faecalis, complicated with inferior limb ischemia. A few months later, the patient was admitted to the hospital after the onset of fever preceded by chills, peaks of 38 °C, dysuria, myalgia, and increased inflammation indexes. A relapsed endocarditis was suspected; this clinical suspicion was then confirmed with blood cultures and transesophageal echocardiography, which showed an iso-echogenic mass adherent to the aortic prosthetic valve.

^99mTc-HMPAO-WBC whole-body scintigraphy was performed without discontinuing high-dose antibiotic therapy and resulted in a negative scan (Fig. 6.5a). Two months later, the scintigraphy was repeated without the interference of antibiotics, with acquisitions at 3 h (Fig. 6.5b) and at 24 h (Fig. 6.5c). The scan revealed a focal area of increased accumulation of labeled leukocytes in the mediastinum (arrow). The fused SPECT/CT image confirmed localization of the focus of infection in the aortic graft (arrow).

Fig. 6.5

See text

6.1.5.2 Suspected Site of Disease

Infection of the aortic composite valve graft.

6.1.5.3 Radiopharmaceutical Activity

^99mTc-HMPAO-WBC, 530 MBq.

6.1.5.4 Imaging

Planar acquisitions at 3 and 24 h after administration of the radiolabeled leukocytes. SPECT/CT imaging acquired after acquisition of planar images.

6.1.5.5 Conclusion/Teaching Points

When planning scintigraphy with labeled autologous leukocytes, attention must be paid to the current therapy administered to the patient. Several antibiotics can alter leukocytes motility, thus increasing the risk of a false-negative result. When clinical signs strongly suggest the presence of an infectious focus, a negative ^99mTc-HMPAO-WBC scintigraphy should be repeated after withholding antibiotic therapy for an adequate period.

6.1.6 Case 6.6

6.1.6.1 Background

An 84-year-old man with aortic graft implanted 6 months earlier and recent development of fever, pre-sternal fluid collection, and high level of ESR, C-reactive protein, and leukocyte count.

[¹⁸F]FDG PET/CT was performed because of clinical suspicion of infection of the aortic graft. Tomographic sections of the chest at different levels in the transaxial (Fig. 6.6a–c), coronal (Fig. 6.6d), and sagittal (Fig. 6.6e) planes, and 3D surface volume rendering of PET/CT fused with angiography (Fig. 6.6f) show aortic valve and distal graft (white arrow in Fig. 6.6a, d, f) focal uptakes (SUV_max 5.5) associated with sternum and soft tissues fluid collection (black arrow in Fig. 6.6c–e) and mediastinum fistula (arrowhead in Fig. 6.6b, c, e) uptakes (SUV_max 4.8).

Fig. 6.6

See text

6.1.6.2 Suspected Site of Disease

Aortic graft, sternum.

6.1.6.3 Radiopharmaceutical Activity

[¹⁸F]FDG, 330 MBq.

6.1.6.4 Imaging

Unenhanced CT and PET images were acquired consecutively 60 min after injection of 330 MBq of [¹⁸F]FDG using a PET/CT system combining a multislice spiral CT scanner with a full-ring PET scanner. Arterial contrast-enhanced CT was obtained after the injection of 135 mL iodinated contrast media.

6.1.6.5 Conclusion/Teaching Points

The use of [¹⁸F]FDG PET/CT and CT angiography with fusion imaging offers great help not only for detecting the presence of infectious foci but also for localizing precisely the site(s) of infection.

6.1.7 Case 6.7

6.1.7.1 Background

A 2-year-old child affected by immune deficiency because of chromosome 22q11.2 deletion (DiGeorge syndrome) with conotruncal heart defects was treated with implantation of a BioPulmonic^® valve in the right ventricular outflow tract. Fever and increased serum levels of the inflammation indexes suggested to perform [¹⁸F]FDG PET/CT, after a CT angiography yielded inconclusive findings.

Tomographic sections in the transaxial (Fig. 6.7a, b) and coronal (Fig. 6.7c) planes, and 3D surface volume rendering of PET/CT fused with angiography (Fig. 6.7d, e) show focally increased [¹⁸F]FDG uptake in the bioconduit valve (dashed red line in a and c) (SUV_max 4, arrow), thus confirming the clinical suspicion of infection.

Fig. 6.7

See text

The BioPulmonic^® valve was replaced, and microbiology of the explanted valve confirmed infection due to Staphylococcus aureus, Staphylococcus epidermidis, and saccharomyces.

6.1.7.2 Suspected Site of Disease

BioPulmonic^® valve.

6.1.7.3 Radiopharmaceutical Activity

[¹⁸F]FDG, 55 MBq.

6.1.7.4 Imaging

After sedation, unenhanced CT and PET images were acquired consecutively 60 min after injection of [¹⁸F]FDG using a PET/CT system combining a multislice spiral CT scanner with a full-ring PET scanner. For post-acquisition processing, the [¹⁸F]FDG PET/CT and arterial-phase contrast-enhanced CT images were fused using a dedicated workstation, in order to define the precise anatomical position of the site(s) of focally increased [¹⁸F]FDG uptake.

6.1.7.5 Conclusion/Teaching Points

A patient with prior cardiovascular prosthesis and clinical suspicion of infection should undergo [¹⁸F]FDG PET/CT to look for infection of vascular prosthesis after an inconclusive CT angiography. Post-acquisition processing for fusion imaging can help to localize more precisely the site of infection in particular settings such as a child with biologic prosthesis.