Differentiating Enostosis vs. Sclerotic Metastasis

When encountering a sclerotic medullary lesion, these features favor a benign enostosis over metastasis:

1. spiculated margins blending into trabeculae

2. the long axis paralleling the host bone

3. complete MRI signal void on all sequences

4. absolutely no surrounding marrow edema—a T2 hyperintense "halo" strongly favors metastasis

5. stability on serial imaging—growth >25% within one year warrants biopsy

Multiplicity in an older adult, particularly with a known breast or prostate primary, should reflexively raise suspicion for metastatic disease over the benign diagnosis.