Cortical Irregularity/Periosteal Reaction
Moderate evidence supports the use of an MRI scan (or CT if MRI is not available) for evaluation of cortical irregularity or periosteal reaction in patients with a potentially malignant bone tumor.

Rationale
As aggressive tumors grow inside or adjacent to bone, eventually the bone cortex will be encountered and breached. Cortical destruction suggests an underlying malignancy or active process, and can be suspected on plain radiographs by identifying a clear cortical perforation, erosion of the cortex, or the host response to tumor invasion manifested as a periosteal reaction. When a cortical irregularity or periosteal reaction is noted, often further assessment is required to determine if the radiographic findings are due to a malignancy, benign tumor, or non-neoplastic condition such as a stress fracture. Two moderate quality studies (Einstien 2015 and Slavotinek 1991) found that plain radiographs, MRI and CT have demonstrated an excellent diagnostic performance in identifying the presence or absence of a periosteal reaction or cortical erosion in patients with malignant bone/soft tissue tumors as compared with the gold standard of histologic diagnosis. A CT scan may or may not provide additional clinical information, depending on the scenario. There is one high quality investigation (Schima 1994) demonstrating 100% sensitivity and 69% specificity when using MRI to determine whether joint invasion is present.

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