PET/MR of pediatric bone tumors: what the radiologist needs to know

Abstract

Integrated 2-deoxy-2-[fluorine-18]fluoro-D-glucose (¹⁸F-FDG) positron emission tomography (PET)/magnetic resonance (MR) imaging can provide "one stop" local tumor and whole-body staging in one session, thereby streamlining imaging evaluations and avoiding duplicate anesthesia in young children. ¹⁸F-FDG PET/MR scans have the benefit of lower radiation, superior soft tissue contrast, and increased patient convenience compared to ¹⁸F-FDG PET/computerized tomography scans. This article reviews the ¹⁸F-FDG PET/MR imaging technique, reporting requirements, and imaging characteristics of the most common pediatric bone tumors, including osteosarcoma, Ewing sarcoma, primary bone lymphoma, bone and bone marrow metastases, and Langerhans cell histiocytosis.

Keywords: Bone sarcoma; Magnetic resonance; PET/MR; Pediatric cancer; Positron emission tomography.

Fig 1.

Example of the 18F-FDG-PET/MR Imaging Workflow

Fig. 2.

Telangiectatic osteosarcoma of the left tibia in an 11-year-old male presenting with left leg pain and mass. a. Lateral radiograph demonstrates an expansile mixed lucent and sclerotic lesion of the proximal left tibial metaphysis extending into the diaphysis. There is moderate cortical destruction with sunburst type periosteal reaction and a partially calcified anterior soft tissue mass. b. Sagittal T1-weighted MR image showing a heterogeneously hypointense expansile tumor of the proximal tibia with extensive cortical destruction and aggressive periosteal reaction. c. PET/MR axial T1-weighted fat suppressed fused image demonstrating diffuse heterogenous hypermetabolism of the mass (SUV max 6.2). d. Axial T2-weighted fat suppressed MR image showing numerous fluid-fluid levels throughout the mass.

Fig. 3.

Intermediate grade periosteal chondroblastic osteosarcoma of the left tibia in a 13-year-old female presenting with left lower extremity pain. a. Lateral radiograph and b. sagittal CT image of the left tibia/fibula showing a cortical based lesion involving the anterior proximal tibial diaphysis with aggressive periosteal bone formation and scalloping of the underlying cortex. c. PET/MR sagittal T1-weighted fused image demonstrating a broad based, hypermetabolic soft tissue mass along the anterior proximal diaphysis of the left tibia (SUV max 12.6) with thickening of the underlying anterior cortex. d. Sagittal T1-weighted fat-suppressed post contrast MR image and e. axial PD-weighted fat suppressed MR image showing heterogenous enhancement/hyperintensity of the anterior soft tissue component with small amount of medullary involvement posterior to the mass.

Fig. 4.

Left fibula Ewing Sarcoma in a 10-year-old female patient presenting with a 3–4 month history of left foot drop, left lower extremity pain and paresthesias, and a large nontender mass in her left lower leg. a. Coronal whole body T2-weighted MR, b. PET/MR coronal T2-weighted fused, and c. PET/MR axial T1-weighted fat-suppressed postcontrast images showing a primary T2 heterogenously hyperintense mass arising from the left proximal fibular diaphysis that demonstrates significant ¹⁸F-FDG PET avidity (SUV max 5.6) and enhancement. d. Sagittal T1-weighted and e. T1-weighted fat-suppressed postcontrast MR images of the distal fibula showing discrete T1 hypointense lesions that enhance on postcontrast images, consistent with intramedullary skip lesions.

Fig. 5.

Left scapula Ewing sarcoma in a 15-year- old male presenting with left scapular mass. a. PET/MR whole body coronal MIP and b. PET/MR whole body coronal T1-weighted fat suppressed fused images showing an intensely ¹⁸F-FDG-avid mass centered in the left scapula (SUV max 7.1) with central necrosis. c. Prone axial T2-weighted fat suppressed MR image showing a lobulated, hyperintense mass in the left scapula with large associated soft tissue component and surrounding edema infiltrates the supraspinatus, infraspinatus, and subscapularis muscles. d. Sagittal T1-weighted fat-saturated postcontrast MR image of the left scapula showing enhancement of the mass and infiltration of the surrounding rotator cuff musculature.

Fig. 6.

Langerhans cell histiocytosis of the left scapula discovered on a skeletal survey in a 2-year-old male presenting with right facial nerve palsy and a mass on the right forehead. a. Frontal radiograph of the left scapula showing an expansile, lytic lesion involving the acromion, glenoid, and scapular body with a normal left humerus. b. PET/MR whole body coronal MIP, c. PET/MR whole body coronal T2-weighted fused, and d. axial T2-weighted fat-suppressed MR images showing a highly ¹⁸F-FDG-avid (SUV max 15.8), T2 hypointense lesion involving the left scapular acromion and body.