Nuclear Medicine Imaging of Bone and Joint Infection

Abstract

Bone infection (osteitis and osteomyelitis) can be divided into infection of the peripheral bones, spine, and joint; it can be acute (within the first 8 weeks from onset) or chronic (lasting longer than 8 weeks), and patients of any age range can be affected. The origin of bone infection is most frequently exogenous, following trauma or surgery, or by contiguous spread from adjacent tissues; it is more rarely hematogenous. The incidence of peripheral bone infection in the developed countries is less than 2% per year, but the rate can increase after surgical procedures of an open or closed fracture in an acute setting (2–19%). The diagnosis of bone infection is based on clinical (physical examination, high levels of ESR, RCP, leukocytes, and positive blood and bone cultures) and imaging findings (radiology and nuclear medicine). The first-line diagnostic imaging of choice is almost always radiologic imaging, but according to the recent published guidelines on bone infection diagnosis, nuclear medicine procedures (labeled leukocyte scintigraphy, [¹⁸F]FDG PET/CT, combination of ^99mTc-diphosphonate bone, and ⁶⁷Ga-citrate scans) are recommended to complement or sometimes replace ultrasound, computed tomography, and magnetic resonance imaging. Nuclear medicine and radiological imaging is mandatory to confirm the presence of bone infection as well as to evaluate response to therapy.

Appendices

Examples of Imaging in Patients with Bone and Joint Infection

Fig. 3.1

Baseline ^99mTc-HMPAO-WBC scintigraphy. Upper panel: (a) Planar images (anterior and posterior views, left and right) at 30 min (upper), 4 h (middle), and 20 h (lower) p.i. show mildly increased focal accumulation of labeled leukocytes in the rotula and in the medial condyle of right femur. (b) The transaxial CT (upper left), SPECT (upper right), fused (lower left) SPECT/CT images more precisely localize the site (medial condyle) of leukocyte accumulation. Lower panels: follow-up ^99mTc-HMPAO-WBC scintigraphy performed after antibiotic treatment. (c) Planar images (anterior and posterior, left and right) at 30 min (upper), 4 h (middle), and 20 h (lower) p.i. show complete disappearance of the focus of leukocyte accumulation at the medial condyle of right femur, as also confirmed by the transaxial CT (upper left), SPECT (upper right), fused (lower left) SPECT/CT images (d)

Fig. 3.2

^99mTc-HMPAO-WBC scintigraphy. (a) Spot planar images of the legs in anterior and posterior views 4 h p.i. (upper) and 20 h p.i. (lower) (a) and (b) lateral views at 20 h. The images show abnormal accumulation of labeled leukocytes at the left leg, without however the possibility to distinguish bone from soft tissue involvement. This case highlights the need of acquiring always the same projections at early and delayed time points. Furthermore, images should be acquired for the same period of time corrected for isotope decay, rather than with a pre-set number of counts, in order to compare all images with same grading of activity, thus defining more easily areas with radioactive accumulation increasing over time (or vice versa declining over time)

Fig. 3.3

^99mTc-HMPAO-WBC scintigraphy. The coronal (a) and transaxial (b) SPECT/CT sections demonstrate labeled leukocyte accumulation in cortical bone near the metallic implants and soft tissues

Fig. 3.4

^99mTc-HMPAO-WBC scintigraphy. Planar spot images (anterior and posterior views left and right, respectively) 4 h p.i. (a) and 24 h p.i. (b). The images show increased accumulation, stable overtime, of labeled leukocytes in the proximal and middle diaphyseal portion of left tibia, suggesting inflammation without infection

Fig. 3.5

^99mTc-colloid scintigraphy. Planar spot anterior view acquired 30 min p.i., showing tracer uptake in the same site as the labeled leukocytes in the prior scintigraphy. This finding confirms the presence of bone marrow at the site of interest, thus ruling out of the presence of acute infection

Fig. 3.6

^99mTc-HMPAO-WBC scintigraphy performed to evaluate the extent of infection. The planar spot views (anterior and posterior, left and right) at 4 h (a) and 24 h (b) p.i. show increased accumulation of labeled leukocytes in the diaphysis of left tibia. The coronal (c), sagittal and transaxial (d) SPECT/CT images allow precise assessment of the extent of infection in the affected bone and the adjacent soft tissues

Fig. 3.7

^99mTc-HMPAO-WBC scintigraphy. (a) Planar images (anterior and posterior, left and right) at 30 min (upper), 4 h (middle), and 20 h (lower) p.i. show increased accumulation of labeled leukocytes, changing in shape, at the proximal portion of the diaphysis of right tibia. (b) The transaxial CT (upper left), SPECT (upper right), and fused (lower left) images, as well as (c) the fused coronal SPECT/CT images and (d) the fused sagittal SPECT/CT images allow precise identification of the site of leukocyte accumulation. These findings are consistent with tibial osteomyelitis (OM). (e) and (f): Follow-up ^99mTc-HMPAO-WBC scintigraphy performed after antibiotic treatment. The planar images (anterior and posterior, left and right) at 30 min (upper), 4 h (middle) and 20 h (lower) (e) p.i. show complete disappearance of the leukocyte accumulation at the proximal portion of the diaphysis of right tibia, but appearance of mild accumulation, declining over time, at the middle portion of the diaphysis of right tibia. These findings confirmed by the transaxial CT (upper left), SPECT (upper right), and fused (lower left) SPECT/CT images (f) are consistent with disappearance of tibial OM and associate with persistence of inflammation at the middle portion of the diaphysis of right tibia

Fig. 3.8

^99mTc-HMPAO-WBC scintigraphy. (a) Planar images (anterior and posterior, left and right) at 30 min (upper), 4 h (middle), and 20 h (lower) p.i. show accumulation of labeled leukocytes at the forefoot, changing in shape. (b) The fused transaxial, coronal, and sagittal SPECT/CT images allow precise identification of the site of leukocyte accumulation, which in soft tissues under the heel without bone involvement

Fig. 3.9

Patient with deep sternal wound infection: planar images (anterior view) at 4 h (left) and 20 h (right) p.i. of ^99mTc-HMPAO-WBC. The images show the increased leukocyte accumulation at the sternum increasing from the 4 h to the 24 h acquisition. The diffuse and intense sternal uptake at 20 h is greater than liver activity

Fig. 3.10

Patient with superficial sternal wound infection. Planar images (anterior view) at 4 h (left) and 20 h (right) p.i. of ^99mTc-HMPAO-WBC. The images show mildly increased activity with time and irregular sternal uptake in the 4 h image

Fig. 3.11

Patient without sternal wound infection. Planar images (anterior view) at 4 h (left) and 20 h (right) p.i. of ^99mTc-HMPAO-WBC. The images show mild and uniform sternal distribution (comparable to other bones of the ribcage), with a midline longitudinal defect due to surgical scar. Sternal activity does not increase with time

Fig. 3.12

^99mTc-HMPAO-WBC scintigraphy. Planar images (anterior and posterior, left and right) at 30 min (upper), 4 h (middle), and 20 h (lower) p.i. show accumulation of labeled leukocytes, increasing overtime and changing in shape, at right femur (head and neck). These findings are consistent with osteomyelitis involving also the adjacent anterior soft tissues, as later confirmed by microbiological culture of biopsy

Fig. 3.13

^99mTc-HMPAO-WBC scintigraphy. (a) Total body images (anterior and posterior, left and right) at 30 min p.i. (a) showing focally reduced accumulation in thoracic skeleton. (b) Planar images (anterior and posterior, left and right) at 4 h (upper) and 20 h (lower) p.i. show an accumulation of labeled leukocytes, increasing over time and changing in shape, at left femur and tibia. (c) Fused sagittal SPECT/CT images allow precise identification of the site of leukocyte accumulation in the femur (above the medial condyle) and tibia (below the medial plate). (d) The lack of uptake in a thoracic vertebral body was confirmed in the transaxial CT (upper left), SPECT (upper right), and fused (lower left) SPECT/CT images at 4 h. These findings are consistent with femural and tibial OM with suspected infection of the thoracic spine

Fig. 3.14

[¹⁸F]FDG PET/CT. (a) The baseline sagittal images (CT left; PET middle; fused right) of the lumbosacral skeleton show increased [¹⁸F]FDG uptake at L5–S1 region (lower region of L5, disk space L5–S1, and upper region of S1). (b) Four months later, the follow-up sagittal images (CT left; PET middle; fused right) performed during antibiotic treatment show a significant reduction of [¹⁸F]FDG uptake at the L5–S1 region, thus demonstrating good response to therapy

Fig. 3.15

[¹⁸F]FDG PET/CT in a patient with suspected post-surgical thoracic spondylodiscitis. The sagittal images (CT left; PET middle; fused right) of the thoracic spine show increased [¹⁸F]FDG uptake in the posterior para-vertebral and para-hardware soft tissues. The scan is compatible with the presence of infection

Fig. 3.16

[¹⁸F]FDG PET/CT in a patient with dorsolumbar spondylodiscitis. (a) The sagittal images (CT left; PET middle; fused right) show increased [¹⁸F]FDG uptake in the T12–L1 region (lower region of T12 and upper region of L1). (b) The transaxial images (CT left; PET middle; fused right) of T12 confirmed increased [¹⁸F]FDG uptake, consistent with infection

Fig. 3.17

[¹⁸F]FDG PET/CT in a patient with thoracic spondylodiscitis. (a) The sagittal images (CT left; PET middle; fused right) show increased [¹⁸F]FDG uptake in the region T10–T11. (b) The fused images (coronal left; sagittal middle; transaxial right) show the extension of abnormal [¹⁸F]FDG uptake in the T10–T11 region, confirming infection

Fig. 3.18

[¹⁸F]FDG PET/CT in a patient with thoracic spondylodiscitis. (a) The baseline fused images (coronal left; sagittal middle; transaxial right) show increased [¹⁸F]FDG uptake in the T8–T9 region. (b) The follow-up fused images (coronal left; sagittal middle; transaxial right) performed after 6 months of antibiotic treatment show the disappearance of detectable [¹⁸F]FDG uptake in the T8–T9 region

Fig. 3.19

[¹⁸F]FDG-PET/CT in a patient with suspected lumbar spondylodiscitis. The transaxial images (CT upper left; PET upper right; fused lower left) of the lumbar spine show increased [¹⁸F]FDG uptake in the posterior para-vertebral soft tissues in the L4–L5 region, with partial bone involvement (spinous process of L5). The scan allows correct evaluation of disease extent

Fig. 3.20

[¹⁸F]FD-PET/CT in a patient with fever, back pain, and pleural effusion revealed at chest X-ray. The PET images (upper panels) do not show significant uptake in the pleural effusion, while intense [¹⁸F]FDG uptake can be seen in some vertebral bodies. The PET finding was consistent with active extrapulmonary tuberculosis (TB). Spine biopsy showed a necrotizing granulomatous inflammation with Langerhans giant cells, thus confirming the diagnosis of vertebral TB

Fig. 3.21

^99mTc-HMPAO-WBC scintigraphy in a patient with infective arthritis of right hip. Planar anterior and posterior images (left and right images, respectively) at 4 h and 24 h p.i. of labeled leukocytes clearly show accumulation of activity increasing with time in the right hip joint, with appearance of a fistula at 24 h, associated soft tissue infection. Almost invariably, fistulae can be seen only in the 24 h scan. In case of a superficial infection, the wound must be medicated and cleaned before each image acquisition, in order to avoid false positivity due to accumulation of radioactive pus in the bandage

Fig. 3.22

^99mTc-HMPAO-WBC scintigraphy in a patient with suspected right knee arthritis. Planar anterior (left) and posterior (right) images at 1 h (upper) and 6 h (lower) p.i. show abnormal accumulation of labeled leukocytes, increasing with time, in the medial region of the right knee joint, indicating the presence of infected arthritis

Fig. 3.23

^99mTc-HMPAO-WBC scintigraphy in a patient with suspected left knee arthritis. Planar anterior (left) and posterior (right) images at 30 min (upper), 4 h (middle), and 20 h (lower) p.i. show abnormal accumulation of labeled leukocytes, increasing with time, in the medial and lateral region of the left knee, indicating the presence of infected arthritis

Fig. 3.24

^99mTc-HMPAO-WBC scintigraphy. (a) Planar anterior (left) and posterior (right) images at 1 h (upper), 3 h (middle), and 20 h (lower) p.i. show abnormal accumulation of labeled leukocytes, increasing with time, at right fibular malleolus. These findings are consistent with infectious disease. (b) MRI of right ankle showed abnormal MR signals, probably due to reactive sclerosis, edema, and inflammatory disease of cancellous bone, with extension to soft tissues around the right fibular malleolus. The ^99mTc-HMPAO-WBC scan and MRI findings are consistent with the presence of a Brodie abs cess

Fig. 3.25

^99mTc-HMPAO-WBC scintigraphy. Posterior (upper) and anterior (lower) planar images at 4 h (a) and 24 h (b) p.i., showing increased abnormal accumulation of labeled leukocytes, increasing with time, at the medium region of left tibiotarsal joint, with extension to soft tissues through a fistula

Fig. 3.26

[¹⁸F]FDG PET/CT. (a) Transaxial and (b) coronal sections of fused PET/CT showing increased [¹⁸F]FDG uptake along the middle portion of diaphysis of left tibia and all along the left tibiotarsal joint

Fig. 3.27

[¹⁸F]FDG PET/CT and ^99mTc-HMPAO-WBC fused image (post-acquisition processing). In this sagittal section, it is possible to distinguish accumulation of the two different radiopharmaceuticals: ^99mTc-HMPAO-WBC are localized in the inferolateral region of the calcaneous, whereas [¹⁸F]FDG is localized in the upper region of the joint and in the plantar region of the foot. The two different radiopharmaceuticals localize at different sites because they target different biological events, therefore different specificities. In this case, [¹⁸F]FDG concentrates in healing tissues and inflammatory reaction, while ^99mTc-HMPAO-WBC accumulate in the infected portion of the joint

Fig. 3.28

^99mTc-HMPAO-WBC scintigraphy in a patient with infectious arthritis of left knee and inflammatory arthritis of right knee. (a) Planar anterior (left) and posterior (right) views at 30 min (upper), 4 h (middle), and 20 h (lower) p.i., clearly showing an increase of activity with time in the left joint and an apparent decline in accumulation of labeled leukocytes in the right knee. (b) Fused SPECT/CT transaxial (upper left), coronal (upper right), and sagittal (lower left) images, identifying the anatomical sites of leukocytes accumulation

Fig. 3.29

⁶⁷Ga-citrate scintigraphy: whole-body images (anterior, left and posterior, right) at 6 h (a) and 24 h (b) p.i., showing increased radiotracer uptake in right shoulder

Fig. 3.30

⁶⁷Ga-citrate scintigraphy. Spot images of the chest in anterior (right) and posterior (left) views obtained at 24 h (upper), 48 h (middle), and 72 h (lower) p.i., showing markedly increased tracer uptake in right shoulder

Fig. 3.31

⁶⁷Ga-citrate scintigraphy, with SPECT/CT acquisition at 48 h p.i. Fused transaxial (a) and coronal (b) images showing intense tracer uptake in the right shoulder, suggesting infectious arthritis. Due to the low specificity of ⁶⁷Ga-citrate scintigraphy, fine-needle aspiration biopsy for microbiology culture is mandatory for final diagnosis. In this case, the scan indicates that there are no other sites of suspected infection in the body. In addition, ⁶⁷Ga-citrate scintigraphy may also serve for post-therapy follow-up

Clinical Cases

3.1.1 Case 3.1

• Elena Lazzeri 

3.1.1.1 Background

A 55-year-old man with fever, chronic pain at both knees, and long-lasting increase of inflammation indexes for rheumatoid arthritis; positive blood culture for Staphylococcus aureus. Transthoracic and trans-esophageal echocardiograms showed mitral valvular regurgitation. For the suspicion of infective endocarditis, [¹⁸F]FDG PET/CT was performed, after a low carbohydrate/high fat diet for 24 h. No [¹⁸F]FDG uptake was detectable at heart valves, whereas a focal area of increased tracer uptake was observed in the upper lobe of left lung (MIP image in lower right panel of Fig. 3.32a). In addition, increased [¹⁸F]FDG uptake was found at bilateral knee joints (transaxial CT, PET, and fused PET images). These findings were consistent with lung infection and suspected for septic involvement of chronic arthritis.

Fig. 3.32

[¹⁸F]FDG-PET/CT (a). The transaxial CT (upper left), PET (upper right), fused (lower left) show high uptake of [¹⁸F]FDG at left lung (superior lobe) and a diffuse and high uptake of [¹⁸F]FDG at main joints particularly evident at knees (left higher than right). These findings are consistent with the presence of inflammatory and/or infective disease. ^99mTc-HMPAO scintigraphy was performed 3 days later, to differentiate inflammatory and/or infective knees joint disease. Planar anterior (left) and posterior (right) images 30 min (upper) 4 h (middle) and 20 h (lower) p.i. (b) clearly showing an increase of activity over time in the right joint and a seeming stable accumulation of labeled leukocytes at the left knee. Semiquantitative evaluation, drawing regions of interest in the target and background regions, confirms the decrease of activity at the left knee. Fused SPECT/CT images (CT upper left; SPECT upper right; fused lower left) (c) show the anatomical regions of leucocytes accumulation. These findings are consistent with infective arthritis of right knee and inflammatory disease of left knee

^99mTc-HMPAO-WBC scintigraphy was therefore performed for the differential diagnosis between septic and inflamed knee arthritis (planar images at 30 min, 4 h, and 20 h in Fig. 3.32b; SPECT/CT images at 4 h in Fig. 3.32c). The scan showed accumulation of labeled leukocytes at both knee joints, increasing over time especially in the right knee.

3.1.1.2 Suspected Site of Infection

Infected knees arthritis.

3.1.1.3 Radiopharmaceutical Activity

[¹⁸F]FDG, 276 MBq.

^99mTc-HMPAO-WBC, 740 MBq.

3.1.1.4 Imaging

[¹⁸F]FDG PET/CT acquired 60 min post-injection, including CT scout view (120 kV, 10 mA), whole-body CT scan (140 kV, 80 mA), and PET (3 min/FOV). Images were reconstructed with and without attenuation correction using the low-dose transmission CT scan.

^99mTc-HMPAO-WBC scintigraphy: acquisition of planar images at 30 min, 4 h, and 20 h; SPECT/CT acquisition at 4 h.

3.1.1.5 Conclusion/Teaching Point

[¹⁸F]FDG PET/CT identified the sites of infection/inflammation, without however the possibility to discriminate between infection and inflammation. ^99mTc-HMPAO-WBC scintigraphy identified septic arthritis at the right knee and inflammation at the left knee.

3.1.2 Case 3.2

• Napoleone Prandini 

3.1.2.1 Background

A 67-year-old man with pain in right foot, resistant to various therapy with nonsteroidal anti-inflammatory drugs (no obvious fever). ^99mTc-HMPAO-WBC scintigraphy was performed which allows to diagnose the presence of bone infection of the right foot.

Planar imaging demonstrated clear accumulation of labeled leukocytes at the right foot, persisting over time between 1 and 20 h (Fig. 3.32a). This finding indicates the presence of infection, which was better localized as talonavicular infection by SPECT/CT imaging acquired at 20 h (fused images in different planes shown in Fig. 3.32b; 3D surface volume rendering in Fig. 3.32c).

3.1.2.2 Suspected Site of Infection

Right foot.

3.1.2.3 Radiopharmaceutical Activity

^99mTc-HMPAO-WBC, 740 MBq.

3.1.2.4 Imaging

Planar scan of lower limbs at 1 h, 4 h, and 24 h; SPECT/CT acquired at 4 h (Figs. 3.33, 3.34, and 3.35).

Fig. 3.33

^99mTc-HMPAO scintigraphy. Anterior scan images of lower limbs 1 h (a), 4 h (b), and 24 h (c) p.i. The images show accumulation of labeled leukocytes in right tarsus increasing over time, indicating infection. Increased activity in ipsilateral inguinal lymph nodes confirms this diagnosis

Fig. 3.34

^99mTc-HMPAO scintigraphy. Fused SPECT/CT images (transaxial, left; sagittal, middle; coronal, right) of feet 4 h p.i. of labeled leukocytes. The images show a focal uptake of labeled leukocytes in right talo-navicular joint consistent with septic arthritis

Fig. 3.35

^99mTc-HMPAO scintigraphy. 3D surface volume rendering of SPECT/CT imaging, showing focal accumulation of labeled leukocytes in the right talo-navicular joint without CT signs of bone structure changes

3.1.2.5 Conclusion/Teaching Point

SPECT/CT imaging during ^99mTc-HMPAO-WBC scintigraphy precisely identifies the site of infection.

3.1.3 Case 3.3

• Elena Lazzeri 

3.1.3.1 Background

A 79-year-old woman with neck pain, increase of inflammation indexes and positive blood culture positive for Staphylococcus aureus. MRI of the cervical spine showed the presence of an anterior epidural abscess collection with concomitant cortical alterations of the vertebral bodies of C5, C6, and C7 consistent with spondylodiscitis (Fig. 3.36: (a) sagittal T1 image with low signal intensity and (b) sagittal STIR image with high signal intensity in the C5–C7 spine region).

Fig. 3.36

MRI: Sagittal T1 image (a) with low signal intensity, and sagittal STIR image (b) with high signal intensity in the C5–C7 spine region. These findings are consistent with infection

[¹⁸F]FDG PET/CT was performed to confirm the presence of spondylodiscitis and also to evaluate with whole-body imaging potential septic embolism. Increased [¹⁸F]FDG uptake was observed in the cervical spine, involving C5, C6, and C7; furthermore, unexpected bilateral pleural effusion was found, with mild tracer accumulation (Fig. 3.37).

Fig. 3.37

[¹⁸F]FDG PET/CT. The sagittal images (CT left; PET middle; fused right) of the skeleton (a) show increased [¹⁸F]FDG uptake in the region C5–C7 and mild increase of uptake at the T3–T4 space. The transaxial fused images (b) show the extension of pathological uptake of [¹⁸F]FDG at the cervical vertebral bodies. These findings confirm the presence of infection of the cervical spine and the suspicion of thoracic spine involvement

The follow-up [¹⁸F]FDG PET/CT scan performed after 2 months of antimicrobial therapy showed considerable reduction of [¹⁸F]FDG uptake both at the cervical region and in the bilateral pleural effusion (Fig. 3.38), indicating partial response to therapy.

Fig. 3.38

[¹⁸F]FDG PET/CT. The follow-up [¹⁸F]FDG PET/CT sagittal images (CT left; PET middle; fused right) (a) performed 3 months later during antibiotic therapy, show a significant reduction of [¹⁸F]FDG uptake in the C5–C7 region and the persistence of mild tracer uptake at the T3–T4 space. The transaxial fused images (b) confirm the marked decrease of pathological uptake of [¹⁸F]FDG at the cervical vertebral bodies. These findings are consistent with a good response to therapy for the cervical spine infection and allow to diagnose the presence of inflammatory disease at the T3–T4 region

3.1.3.2 Suspected Site of Infection

Cervical spine.

3.1.3.3 Radiopharmaceutical Activity

[¹⁸F]FDG, 276 MBq.

3.1.3.4 Imaging

[¹⁸F]FDG PET/CT acquired 60 min post-injection, including CT scout view (120 kV, 10 mA), whole-body CT scan (140 kV, 80 mA), and PET (3 min/FOV). Images were reconstructed with and without attenuation correction using the low-dose transmission CT scan.

3.1.3.5 Conclusion/Teaching Point

[¹⁸F]FDG PET/CT confirmed the clinical suspicion of cervical spine infection and ruled out septic embolism. The persistence of [¹⁸F]FDG uptake in the cervical spine during the follow-up PET/CT scan (although reduced versus the baseline scan) does not permit to establish a sure differential diagnosis between persistence of infection and presence of inflammation only.

3.1.4 Case 3.4

• Elena Lazzeri 

3.1.4.1 Background

A 36-year-old man with fever, pain at the left gluteal region, and positive blood culture for Staphylococcus aureus. MRI of the lumbar spine showed the presence of a median hernia at L5–S1 with limited cord and spinal compression without evidence of infection and/or pathology of cauda.

PET/CT with [¹⁸F]FDG was performed to definitely rule out the clinical suspicion of spondylodiscitis. The PET/CT scan was negative for infection of the lumbosacral spine, whereas markedly increased [¹⁸F]FDG uptake was observed in the right sacroiliac joint and the adjacent soft tissues (Fig. 3.39). These findings suggest the presence of infection of the right sacroiliac joint with involvement of adjacent soft tissues. A repeat MRI scan performed 1 week later became positive for infection/inflammation (Fig. 3.40).

Fig. 3.39

[¹⁸F]FDG PET/CT. The coronal (a), sagittal (b), and transaxial (c , d) images (CT, PET, and fused) show increased [¹⁸F]FDG uptake at the right sacroiliac joint, with involvement of the anterior soft tissues of the pelvic plane

Fig. 3.40

MRI: Coronal (a) and transaxial (b) images show impaired signal and contrast enhancement of articular surfaces of the right sacroiliac joint, with edema of the soft tissues consistent with inflammatory reaction

3.1.4.2 Suspected Site of Infection

Lumbosacral spine.

3.1.4.3 Radiopharmaceutical Activity

[¹⁸F]FDG, 260 MBq.

3.1.4.4 Imaging

[¹⁸F]FDG PET/CT acquired 60 min post-injection, including CT scout view (120 kV, 10 mA), whole-body CT scan (140 kV, 80 mA), and PET (3 min/FOV). Images were reconstructed with and without attenuation correction using the low-dose transmission CT scan.

3.1.4.5 Conclusion/Teaching Point

PET/CT with [¹⁸F]FDG identified the etiology of fever, leading to establish a final diagnosis of right infective sacroiliitis. Following high-dose antibiotic treatment (linezolid i.v.), both fever and the back pain markedly declined within about 15 days after onset of treatment.

3.1.5 Case 3.5

• Napoleone Prandini 

3.1.5.1 Background

A 77-year-old woman with polyarthritis and rheumatoid arthritis presenting with fever and pain at both shoulders and both knees. The patient was referred for PET/CT with [¹⁸F]FDG, which demonstrated increased tracer uptake in both shoulders (but predominant in left shoulder) and in left wrist (Fig. 3.41), indicating the presence of infection and/or inflammation at these sites.

Fig. 3.41

[¹⁸F]FDG PET/CT showed increased tracer uptake predominantly in the left shoulder and in left wrist

^99mTc-HMPAO-WBC scintigraphy was then performed to better characterize the multiple sites of increased [¹⁸F]FDG uptake. Abnormal accumulation of labeled leukocytes was observed in both shoulders (predominantly in left shoulder) and both knees (of mild degree), but not in left wrist (Figs. 3.42 and 3.43).

Fig. 3.42

^99mTc-HMPAO-WBC scintigraphy: total-body scan 1 h, 4 h, and 20 h p.i. The images show significantly increased accumulation of labeled leukocytes in the articular cavity of both shoulders and knees

Fig. 3.43

^99mTc-HMPAO-WBC scintigraphy. SPECT/CT acquisition of the shoulders obtained at 4 h showed increased accumulation of labeled leukocytes in the left joint shoulder cavity, indicating septic arthritis

3.1.5.2 Suspected Site of Infection

Both shoulders and both knees.

3.1.5.3 Radiopharmaceutical Activities

[¹⁸F]FDG, 270 MBq.

^99mTc-HMPAO-WBC, 740 MBq.

3.1.5.4 Imaging

[¹⁸F]FDG PET/CT acquired 60 min post-injection, including CT scout view (120 kV, 10 mA), whole-body CT scan (140 kV, 80 mA), and PET (3 min/FOV). Images were reconstructed with and without attenuation correction using the low-dose transmission CT scan.

^99mTc-HMPAO-WBC scintigraphy: acquisition of planar images at 1 h, 4 h, and 20 h; SPECT/CT acquisition at 4 h.

3.1.5.5 Conclusions/Teaching Point

PET/CT with [¹⁸F]FDG showed high tracer uptake in both shoulders and left wrist (because of technical malfunction, the knees were not included in the scan). ^99mTc-HMPAO-WBC scintigraphy showed increased leukocyte accumulation predominantly in left shoulder, with no accumulation at all in left wrist. The most likely diagnosis in this patient was infective arthritis of left shoulder, with concomitant inflammation of right shoulder, left wrist, and both knees.