Distinguishing Osteomyelitis From Ewing Sarcoma on Radiography and MRI

Abstract

Objective: The purpose of this study was to determine whether clinical and imaging features can distinguish osteomyelitis from Ewing sarcoma (EWS) and to assess the accuracy of percutaneous biopsy versus open biopsy in the diagnosis of these diseases.

Materials and methods: Three radiologists reviewed the radiographs and MRI examinations of 32 subjects with osteomyelitis and 31 subjects with EWS to determine the presence of 36 imaging parameters. Information on demographic characteristics, history, physical examination findings, laboratory findings, biopsy type, and biopsy results were recorded. Individual imaging and clinical parameters and combinations of these parameters were tested for correlation with findings from histologic analysis. The diagnostic accuracy of biopsy was also determined.

Results: On radiography, the presence of joint or metaphyseal involvement, a wide transition zone, a Codman triangle, a periosteal reaction, or a soft-tissue mass, when tested individually, was more likely to be noted in subjects with EWS (p ≤ 0.05) than in subjects with osteomyelitis. On MRI, permeative cortical involvement and soft-tissue mass were more likely in subjects with EWS (p ≤ 0.02), whereas a serpiginous tract was more likely to be seen in subjects with osteomyelitis (p = 0.04). African Americans were more likely to have osteomyelitis than EWS (p = 0). According to the results of multiple regression analysis, only ethnicity and soft-tissue mass remained statistically significant (p ≤ 0.01). The findings from 100% of open biopsies (18/18) and 58% of percutaneous biopsies (7/12) resulted in the diagnosis of osteomyelitis, whereas the findings from 88% of open biopsies (22/25) and 50% of percutaneous biopsies (3/6) resulted in a diagnosis of EWS.

Conclusion: Several imaging features are significantly associated with either EWS or osteomyelitis, but many features are associated with both diseases. Other than ethnicity, no clinical feature improved diagnostic accuracy. Compared with percutaneous biopsy, open biopsy provides a higher diagnostic yield but may be inconclusive, especially for cases of EWS. Our findings underscore the need for better methods of diagnosing these disease processes.

Keywords: Ewing sarcoma; MRI; osteomyelitis; radiography.

Fig. 1. 19-year-old woman with Ewing sarcoma

A, Radiograph with external rotation view of humerus shows permeative cortical process (arrow). B and C, Sagittal T1-weighted (B) (TR/TE, 360/14) and STIR (C) (TR/TE, 3825/30) MR images show cortical thickening (arrows). Note wide transition zone on both sequences and mild deep soft-tissue edema. D, Axial contrast-enhanced T1-weighted (TR/TE, 1080/14) image shows abnormal marrow and abnormal enhancement (arrow) in intact cortex and surrounding soft-tissue edema.

Fig. 2. 3-year-old boy with osteomyelitis of distal radius

A, Anteroposterior radiograph shows cavity (arrow) in distal radial metaphysis. B, Coronal unenhanced T1-weighted (TR/TE, 500/21) MR image windowed to show relatively hyperintense peripheral rim of multilocular penumbra (arrows). C, Coronal contrast-enhanced T1-weighted (TR/TE, 550/14) MR image shows intense enhancement of highly vascularized penumbra (arrows).

Fig. 3. 6-year-old boy with Ewing sarcoma

A, Anteroposterior radiograph of left femur shows multiple cavities (arrows) in proximal diametaphysis. B, Unlike in patient with osteomyelitis shown in Fig. 2B, margins of cavities (arrows) in this patient are dark on T1-weighted (TR/TE, 431/11) MR image. C, Coronal contrast-enhanced T1-weighted (TR/TE, 431/11 ms) MR image shows heterogeneous marrow enhancement and wide transition zone. Note, in contrast to Fig. 2C, that there is no peripheral enhancement of cavities. Substantial deep soft-tissue edema is present.

Fig. 4. 10-year-old boy with Ewing sarcoma

A, Anteroposterior radiograph shows cortical saucerization (arrow) along distal lateral femur. B and C, Coronal STIR (B) (TR/TE, 4845/30) and axial contrast-enhanced T1-weighted (C) (TR/TE, 1080/14) MR images show small soft-tissue mass (arrows) and medullary tumor in area of cortical abnormality. Note wide transition zone on coronal image.

Fig. 5. 13-year-old boy with osteomyelitis

A, Lateral radiograph of distal femur shows sharply defined cortical saucerization (curved arrow) and subtle lucency (straight arrow) in medullary canal. B, Sagittal contrast-enhanced T1-weighted (TR/TE, 710/15) MR image shows enhancing mass (arrow) that was thought to have arisen primarily from soft tissue with secondary involvement of subperiosteum. Pus was drained, and Staphylococcus aureus was isolated from culture.