Tumor Interface
Moderate evidence suggests that characterizing the tumor interface (borders and zone of transition) on MRI and CT may assist with obtaining a diagnosis or planning further diagnostic studies or treatment for bone or soft tissue tumor of unknown etiology.

Rationale
Seven studies were evaluated regarding the use of various imaging modalities for patients undergoing diagnostic work-up for a bone tumor of unknown etiology. There were 4 studies concerning MRI and 3 concerning combined modalities (MRI and CT, MRI and plain films). There were no articles on PET or Tc99 bone scan. The average number of patients per study was 57 (range=28-101). Literature pertaining to the use of MRI for differentiating benign and malignant tumors was diagnosis-specific. Choi et al (low quality) evaluated the ability of MRI to differentiate between enchondroma and low-grade chondrosarcoma in 34 patients. They concluded that, “MR imaging shows helpful features for differentiating low-grade chondrosarcoma from enchondroma.” De Beuckeleer et al (moderate quality) retrospectively reviewed 79 cartilaginous tumors. These included osteochondromas, enchondromas, low-grade chondrosarcomas, and high-grade chondrosarcomas. They concluded that MR features are highly specific but lack sensitivity. Yoo et al (high quality) retrospectively reviewed 42 chondrosarcomas: 28 low-grade and 14 high-grade. They determined that soft tissue mass formation favored high-grade lesions, and intratumoral fat was suggestive of low-grade lesions. Bernard et al (moderate quality) retrospectively compared cartilage cap thickness using CT and MRI to distinguish between osteochondromas and secondary chondrosarcomas; both studies were highly sensitive and specific. Henninger et al identified 28 patients in whom the diagnoses of osteomyelitis and Ewing sarcoma were both considered.

They concluded that STIR MRI sequences most reliably distinguishes between osteomyelitis and Ewing sarcoma. McCarville et al evaluated the use of MRI and CT to distinguish between osteomyelitis and Ewing sarcoma. They were unable to give imaging-based recommendations for diagnosis. Oudenhoven et al (high quality) evaluated the value of MRI in diagnosing bone tumors of the hand. MRI was found to confirm or enhance the diagnostic accuracy of plain radiographs. In conclusion, cross-sectional imaging of some kind (either CT or MR) is helpful in obtaining a diagnosis or planning further diagnostic studies or treatment for bone or soft tissue tumor of unknown etiology with radiographs that show a poorly defined interface with the tumor (e.g. permeative border or wide zone of transition). MRI can greatly enhance the diagnostic accuracy of plain radiographs in bony lesions of the hand. CT of the chest/abdomen/pelvis remains an essential aspect of tumor staging. This will reveal the primary site of metastatic bone tumors in many cases, as well determine the presence or absence of pulmonary metastatic disease in patients with sarcoma.

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