Radionuclide Imaging of Infection and Inflammation in Pediatrics

Abstract

Scintigraphy with radiolabeled autologous leukocytes is a useful and often crucial tool in the evaluation of many infective processes in children. The most common indications include cardiovascular system infections (endocarditis, prosthetic vascular graft infections), orthopedic hardware infections (prosthetic joints, fixation devices), inflammatory bowel disease, and fever of unknown origin. Acquisition and image interpretation of radiolabeled leukocytes scintigraphy in children requires full knowledge of both technical and clinical aspects and a coordinated teamwork of professionals experienced in pediatrics (nuclear medicine physicians, nurses, nuclear medicine technologists). For example, in younger children, it is difficult to obtain a sufficient volume of blood, both for the collaboration of the child during withdrawal of the blood sample for the volume required for separation of the cells. In this chapter, we discuss some interesting cases we dealt with in our Nuclear Medicine Unit, focusing in particular on image features.

Clinical Cases

16.1.1 Case 16.1

16.1.1.1 Background

A 4-year-old boy with severe dilative cardiomyopathy was hospitalized in cardiovascular intensive care unit, waiting to be listed for heart transplantation; a biventricular assist device (BIVAD)—Berlin heart—and a tracheostomy were placed in order to support blood circulation and mechanic ventilation, respectively. On the 95th day of hospitalization, the patient developed fever resistant to antibiotic treatment; swab tests on the skin surrounding BIVAD tubes revealed the presence of Staphylococcus aureus, Escherichia coli, and Klebsiella. The plain chest X-ray showed severe cardiomegaly, a retrocardiac consolidation in left lung, and diffuse interstitial involvement (Fig. 16.1). A radiolabeled leucocyte scintigraphy was performed in order to rule out infection of BIVAD and/or an endocarditis.

Fig. 16.1

Plain chest X-ray, showing severe cardiomegaly, retrocardiac opacity in left lung, and diffuse interstitial involvement

16.1.1.2 Findings

Planar imaging did not show any focus of abnormal accumulation of radiolabeled leukocytes (Fig. 16.2). The manually fused SPECT/CT images showed abnormally high accumulation of the radiolabeled leukocytes into multiple consolidations in both lungs (Fig. 16.3), but no other focal abnormalities were detected in the BIVAD or in the endocardium (Fig. 16.4). Antibiotic therapy was subsequently modified, with resolution of fever.

Fig. 16.2

Planar radiolabeled leukocyte anterior and posterior views, showing normal biodistribution in lungs, liver, and spleen at 5 min (a); a faint area of leukocyte accumulation in the base of left lung is detected at 2 h (b) and at 24 h (c)

Fig. 16.3

Manually fused SPECT/CT images, demonstrating radiolabeled leukocyte accumulation into multiple consolidations in the apical posterior segment of right superior lobe, in the apical segment of the right inferior lobe and in the left inferior lobe, respectively (a, transaxial sections; b, coronal sections); no abnormal accumulation of labeled leukocytes can be detected on the endocardium (c)

Fig. 16.4

Planar radiolabeled leukocyte anterior and posterior views, showing normal biodistribution in lungs, liver, and spleen at 5 min (a), abnormal accumulation in the thorax, near the left side of the sternal manubrium at 2 h (b), increasing in intensity at 24 h (c)

16.1.1.3 Conclusion/Teaching Points

SPECT/CT images are mandatory in order to improve diagnostic accuracy, to define the localization of uptake and to confirm the absence of abnormal uptake evident on static images.

16.1.2 Case 16.2

A 17-year-old boy, followed in our Cardiology Department for Laubry and Pezzi syndrome and aortic insufficiency surgically treated multiple times (last surgery: aortic valve replacement with bioprosthetic valve, 6 years earlier), was referred to the accident and emergency unit for vomit and fever and was hospitalized.

Chest CT showed a large fluid collection in the anterior mediastinum, close to the aortic conduit. Blood culture yielded Staphylococcus aureus, but there were no signs of endocarditis on echocardiography. Suspecting an involvement of the conduct, a radiolabeled leucocyte scintigraphy was scheduled, and appropriate antibiotic therapy was prescribed.

16.1.2.1 Findings

Planar imaging at 2 h showed a focal area of increased accumulation in the thorax, near the left side of the sternal manubrium, increasing in intensity at 24 h (Fig. 16.4). The manually fused SPECT/CT images showed radiolabeled leukocytes accumulation into the known fluid collection detected on the CT scan in anterior mediastinum, but no foci of abnormal accumulation of radiolabeled leukocytes on the aortic conduit nor on the valve (Fig. 16.5).

Fig. 16.5

Manually fused SPECT/CT images, showing accumulation of radiolabeled leukocytes into the fluid collection in anterior mediastinum; no focus of abnormal accumulation of radiolabeled leukocytes is detected on the aortic conduit nor on the valve (a, transaxial sections; b, sagittal section; c, coronal section)

Antibiotic therapy was subsequently modified, and the collection was surgically drained, with resolution of fever. At the end of antibiotic therapy, radiolabeled leucocyte scintigraphy was repeated in order to confirm resolution of the infection. Planar imaging images did not show any focus of abnormal accumulation of radiolabeled leukocytes (Fig. 16.6), and also the manually fused SPECT/CT images confirmed this finding (Fig. 16.7).

Fig. 16.6

Planar radiolabeled leukocyte anterior and posterior views, showing normal biodistribution in lungs, liver, and spleen at 5 min (a); no obvious areas of focal accumulation at 2 h (b) and 24 h (c)

Fig. 16.7

Manually fused SPECT/CT images, showing no evidence of abnormal accumulation in the mediastinum (a, transaxial section; b, sagittal section; c, coronal section)

16.1.2.2 Conclusion/Teaching Points

Radiolabeled leukocyte scintigraphy helps in the differential diagnosis of fluid collections in post-surgical patients (abscess versus sterile collection), allowing better definition of therapeutic management. This procedure is also useful to verify the efficacy of antibiotic therapy.

16.1.3 Case 16.3

A 10-year-old boy with left tibial osteosarcoma, previously treated with chemotherapy, amputation, and implant of prosthesis, 4 months after surgery presented dehiscence of the wound, fever, and pain in the left foot. An ultrasound scan showed nonspecific thickening of soft tissue in left ankle. Left leg and foot showed no signs of osteomyelitis. A radiolabeled leukocyte scintigraphy was performed in order to rule out osteomyelitis.

16.1.3.1 Findings

Planar imaging showed intense accumulation of radiolabeled leukocytes in left foot (Fig. 16.8). The manually fused SPECT/CT images showed abnormally high accumulation of radiolabeled leukocytes in astragalus, around the prosthesis, and additional foci of accumulation in tarsus and metatarsus (Fig. 16.9).

Fig. 16.8

Planar radiolabeled leukocyte static images, showing intense accumulation of radiolabeled leukocytes in left foot at 5 min (a, anterior view), at 2 h (b, anterior view; c, lateral view), and at 24 h (d, anterior view; e, lateral view)

Fig. 16.9

Manually fused SPECT/CT images, showing diffuse radiolabeled leukocytes accumulation in astragalus, around the prosthesis (a, coronal sections), and additional foci of accumulation in tarsus and metatarsus (b, sagittal sections)

Antibiotic therapy was started, with resolution of fever and pain relief within 7 days.

16.1.3.2 Conclusion/Teaching Points

Radiolabeled leukocyte scintigraphy is the examination of choice in patients with suspected infection of prosthetic joint and inconclusive conventional imaging, both in children and in adults, because it is not affected by artifacts from orthopedic hardware, unlike other modalities such as CT.

SPECT/CT images are useful in order to identify the precise anatomical localization of foci of radiolabeled leukocyte accumulation detected on planar imaging.

16.1.4 Case 16.4

An 18-year-old boy with cystic fibrosis followed by the cystic fibrosis unit of our hospital presented abdominal pain and recurring fever for 2 months; an episode of bloody diarrhea also occurred. Therapy with mesalazine lead to prompt relief of pain and resolution of fever, but abdominal pain and bloody diarrhea presented again after discontinuation of therapy. Colonoscopy did not show clear signs of inflammation, but histological examination revealed nonspecific inflammatory infiltration. A radiolabeled leukocytes scintigraphy was scheduled in order to confirm the clinical diagnosis of inflammatory bowel disease.

16.1.4.1 Findings

Planar imaging showed diffuse accumulation of radiolabeled leukocytes in the colon, persisting at 24 and 48 h (Fig. 16.10); this pattern suggested inflammatory bowel disease. Long-term therapy with mesalazine was therefore started again, with resolution of signs and symptoms.

Fig. 16.10

Planar radiolabeled leukocytes anterior views, showing normal biodistribution in liver and spleen at 5 min (a), diffuse radiolabeled leukocyte accumulation in ascending, transverse, and descending colon at 2 h (b) and 24 h (c); abnormal accumulation persisted at 48 h (d)

16.1.4.2 Conclusion/Teaching Points

Radiolabeled leukocyte scintigraphy can help to confirm the diagnosis in patients with symptoms suggestive of inflammatory bowel disease (abdominal pain and/or fever and/or bloody diarrhea), but inconclusive endoscopy. Additional imaging at 48 h is useful to distinguish physiological excretion in the bowel from pathological accumulation of radiolabeled leukocytes.