Think of bone lesions in 4 groups:

Aggressive features

• IDK what it is (aggressive but nonspecific features)

  • Very common in clinical practice; ddx by age.

    • Adult: mets/myeloma

    • Children: ewing/infection

• I know what it is! (lesion w/ characteristic imaging features)

  • Very rare in clinical practice: osteosarcoma, chondrosarcoma.

Nonaggressive features

• IDK what it is (nonaggressive but nonspecific features)

  • Very common in clinical practice; can say fibro-osseous lesion to sound smart.

• I know what it is! (characteristic imaging features)

  • Enchondroma, osteoid osteoma, non-ossifying fibroma, hemangioma, giant cell tumor, fibrous dysplasia.

Benign focus of compact (cortical) bone located w/n cancellous bone (medullary cavity); small spiculated osteoblastic focus

• Location: can be found in any bone; pelvis, long bones (epiphyses, metaphysis), ribs, spine most frequent

• Size: usually small <1 cm; may be giant >2 cm (most difficult to differentiate)

• Morphology: round, oval, oriented along long axis of bone.

• Can be multiple in some bone or polyostotic; if multiple and concentrated in metaphyses and epiphyses = osteopoikilosis

  • Osteopoikilosis: AD syndrome of multiple bone islands and keloid formation.

• Clinically significance: must differentiate from an osteoblastic mets, osteoid osteoma or a low-grade osteosarcoma.

• Bone scan: usually normal

• Osteopathia striata: benign asx sclerotic dysplasia characterized by linear bands of sclerosis in the long bones and fan-like sclerosis in the flat pelvic bones.

DDX

• Sclerotic mets: can have identical appearance; may not be as homogeneous dense throughout. 

  • Mets generally show some enhancement on MR. 

  • Positive PET/CT is helpful; Not exclusionary is lesion is small or underlying suspected mets is not typically FDG-avid (adenoid cystic CA, medullary thryoid, myxoid liposarcoma)

• Nonossifying fibroma

  • Typically not as dense; Generally heal during teenage years w slightly sclerotic bone forming periphery -> eventually replaced by normal bone or leave faint trace of homogeneous sclerosis; 

  • Cortical rather than medullary.

• Osteoma

  • Dense focus; usual location is paranasal sinus or skull. If located peripherally, arises on outer cortex of bone, not w/n marrow. Generally homogeneously sclerotic, though may have regions of inhomogeneity.

• Osteoid osteoma:

  • Usually have lytic nidus +/- central sclerotic focus

  • Nidus may be obscured on radiograph by homogenous sclerotic bone rxn.

    • Lytic nidus always evident wither w CT or MR; extensive regional edema on MR.