Imaging pediatric bone sarcomas

Abstract

Primary malignant bone tumors are rare and account for about 6% of all new pediatric cancer cases per year in the United States. Identification of the lesion not uncommonly occurs as a result of imaging performed for trauma. Clinical and standard imaging characteristics of the various tumor types are evolving in concert with treatment advancements and clinical trial regimens. This article reviews the 3 most common pediatric bone sarcomas-osteosarcoma, Ewing sarcoma, and chondrosarcoma-and their imaging as applicable to contemporary disease staging and monitoring, and explores the roles of evolving imaging techniques.

Figure 1. Skip lesions

15-year-old boy with osteosarcoma (arrows) right humerus at diagnosis. Sagittal mid-humeral MR images with (a) non-contrast T₁-weighted, (b) STIR (short tau inversion recovery) and (c) post-contrast fat saturated T₁-weighted sequences. Note mid-humeral diaphyseal focus of tumor (arrowheads), histologically proven to be a skip metastasis. This lesion is most inspicuous on non-contrast T₁-weighted sequence and becomes in distensible from adjacent edema in STIR sequenced. With contrast enhancement, the skip lesion becomes intense with enhancing edema.

Figure 2. 16 year-old boy with osteosarcoma distal left femur; intramedullary tumor extent best shown on T₁-weighted sequence

A. Anteroposterior and B. lateral views of the left femur show aggressive periosteal reaction (arrows) distal left femur. C. Coronal whole body ^99mTc. MD P bone scan shows intensive metabolic activity within the intramedullary portion of the tumor (arrows) but relative paucity around the periphery of the extra cortical extent laterally (arrowhead). D. Coronal non-contrast T₁ – weighted MR sequence exquisitely demonstrates the intramedullary extent of disease. The arrow indicates the sharp transition from normal bright fatty marrow to dark tumor marrow. Arrowheads delineate the soft tissue portion of disease. E. With contrast administration, the soft tissue mass becomes well-delineated but the intramedullary transition enhances intensely with marrow enhancement.

Figure 3. 13 year-old girl with 3 month history of right knee pain, histologically proven to be Ewing's Sarcoma

Anteroposterior, A, and lateral, B, radiographs of the right knee show a poorly defined, irregular region of metaphyseal demineralization (arrows) with minimal anterior cortical scalloping, B (arrowhead). C, Coronal non-contrast T₁-weighted MR shows the intramedullary line of demarcation of the tumor (long arrow) with mild adjacent poorly defined intramedullary edema (short arrow). Coronal STIR, D, and sagittal post-contrast T₁-weighted image with fat suppression demonstrate the extent of the intramedullary enhancing edema (short arrows). On these two sequences, the increased signal of the edema silhouettes the intramedullary tumor making delineation of tumor from surrounding edema difficult. The axial post-contrast T₁-weighted image with fat saturation, F, confirms these findings but also shows tumor extension through the medial cortex (black arrowhead). Note the similarities in the appearance of the radiographs, soft tissue and intramedullary edema in this case with those in Figure 4.

Figure 4. 9-year-old girl underwent evaluation for left thigh pain of several weeks duration with presumed diagnosis of Ewings sarcoma family of tumors

A. Anteroposterior and B. lateral radiographs of the left femur demonstrate subtle heterogeneous mineralization and layered periosteal reaction along the anterior diaphysis (arrows). These findings correlate with increased metabolic activity shown on the corresponding ^99mTc-MDP bone scan C. (arrow). Within the increased activity left distal femur is a focus of more intense activity (arrow). D. This focus correlates with the tiny cortical abscess demonstrated on axial contrast-enhanced MR (arrow) with fat saturation, indicative of osteomyelitis and confirmed by biopsy.

Figure 5. Dynamic enhanced MRI (DEMRI) (Courtesy of Wilburn E. Reddick, Ph.D.)

14-year-old female with osteosarcoma distal left femur at baseline evaluation. The left-hand image is the final T₁-weighted contrasted enhanced dynamic set. Quantitative T1 relaxation measures before contrast middle image) and dynamic contrast-enhanced (DCE)-MRI (right-hand image) were both acquired as 16 slice 3D acquisitions with 5 mm thick sections covering the full extent of the tumor. A representative section from the center of the imaging volume is shown.the middle image is the Ktrans (transfer rate constant for contrast transfer from plasma to extracellular space) [min⁻¹] image. The right-hand image is ve (fractional extracellular / extravascular space).

Figure 6. 14-year-old girl underwent evaluation of 2 month history of right thigh pain and swelling. She was diagnosed with high grade right femoral periosteal osteosarcoma (arrowhead)

A. The coronal STIR image of the right thigh demonstrates massive edema (arrows) extensively involving the adductor muscles and to a lesser extent, abductor muscles. B. and C. Staging chest CT revealed a non-specific 4mm nodule in the right upper lobe (arrow) which was histologically proven to be acute necrotizing granuloma with bronchiolitis but no evidence of malignancy.

Figure 7. 18-year-old male treated 6 years earlier for osteosarcoma right tibia underwent surveillance PET-CT for monitoring of disease recurrence

A. Fused PET-CT image showing metabolically active metastatic osteosarcoma of the lower pole left kidney (arrows). B. Coronal and C. axial reformatted images from a contrast-enhanced diagnostic abdominal CT scan shows the large left lower pole renal mass with tumor calcifications (arrows)

Figure 8. PET-MR right humeral osteosarcoma (Courtesy of Barry S. Shulkin, MD, MBA)

15 year-old with proximal right humeral osteosarcoma at time of diagnosis. Multiplanar PET-CT images through the right humerus and axial fat saturated T₂-weighted image through the proximal humeral osteosarcoma merged with a comparable image from reconstructed PET-CT study shows intense abnormal metabolic activity most prominent around the periphery of the tumor (arrowheads). Note relative absence of metabolic activity in the associated soft tissue edema (arrows).

Figure 9

Chest CT was performed 2 months after thoracotomy for pulmonary metastectomy, A, and revealed tumor recurrence in right lower lobe scar (arrow), B. Note nodular expansion within the scar. (Courtesy of M. Beth McCarville, MD)