Sunday, March 12, 2017

Fat-containing bone lesions


The presence of fat within a bone lesion is almost always reassuring, although rare exceptions exist. The following differential diagnosis is based on a combination of published papers and my own anecdotal experience:
  • Hemangioma:
  • Intra-osseous lipoma and lipoma variants, including fibrolipoma, angiolipoma and myelolipoma.
  • Enchondroma:
  • Liposclerosing myxofibrous tumor (LSMFT): Nearly all occur in the intertrochanteric region. Now felt to represent a variant of fibrous dysplasia.
  • Osteoporosis: Can give the appearance of lucent bone lesions on CT. These won't have defined margins, and measurement of internal attenuation will reveal the fatty nature of the lesion.
  • Bone infarction: Trivial, but included for the sake of completeness
  • Paget disease of bone:
  • Focal red marrow rest: Ill-defined, intermediate T1 signal. May contain subtle areas of internal fat.
  • Lymphoma: Not truly a fat-containing lesion, but can entrap fat as the tumor infiltrates marrow.
  • Sarcoid: The case above shows a patient with sarcoid and nodal, hepatic, and osseous involvement. Can have fuzzy margins ("brush border").
  • Treated metastasis: One of the ways metastases respond to therapy is by developing internal fat. Myeloma lesions can even entirely "disappear" due to fatty replacement.
  • Indolent metastases: Medullary thyroid cancer, adenoid cystic carcinoma.
  • Intra-osseous hibernoma: Rare.
  • Solid variant of aneurysmal bone cyst:
  • Nonossifying fibroma:
  • Erdheim-Chester disease:
  • Malignancy arising from a fat-containing lesion: For example, osteosarcoma arising from bone infarction or Paget.

References

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