Metastatic Lesions of the Bones



Metastatic Lesions of the Bones


Todd M. Blodgett, MD

Alex Ryan, MD

Hesham Amr, MD





Key Facts


Terminology



  • Bone metastases, metastatic lesions to bone, secondary bone tumors


Imaging Findings



  • More than 80% of metastases to bone are located in axial skeleton where red marrow blood flow is high



    • Vertebrae, ribs, and hips


  • FDG PET generally ineffective for tumors that are not FDG avid



    • Prostate cancer, highly mucinous tumors, occasionally renal cell carcinoma


    • Also limited in some sclerotic metastases


  • o Reveals marrow lesions in FDG-avid disease prior to cortical effects (often before bone scan becomes positive)


  • CT may miss many early infiltrative or osteolytic lesions


  • CT has higher sensitivity for osteoblastic/sclerotic bone metastases


  • F-18 NaF PET: Excellent PET bone agent, currently not reimbursed by Medicare and most third party payers


Top Differential Diagnoses



  • Degenerative Processes, Arthropathies


  • Healing Fracture or Bone Injury


  • Iatrogenic: Vertebroplasty, Kyphoplasty


  • Physiologic Activity


  • Primary Bone Tumors


Pathology



  • Most common childhood primaries: Neuroblastoma, Ewing sarcoma, rhabdosarcoma






Graphic shows a vertebral body image that has been completely replaced with metastatic disease.






Axial CECT shows lytic foci within a vertebral body image in a patient with multiple myeloma; one lesion erodes the posterior vertebral body cortex image.


TERMINOLOGY


Abbreviations and Synonyms



  • Bone metastases, metastatic lesions to bone, secondary bone tumors



    • Sclerotic/osteosclerotic metastases


    • Osteolytic metastases


Definitions



  • Malignant extension to bone, often by carcinoma, due to direct extension, retrograde venous flow, or hematogenous metastasis


IMAGING FINDINGS


General Features



  • Best diagnostic clue: Typical presentation includes scattered lesions in areas of osteoblastic or osteolytic activity


  • Location



    • Seeding occurs mostly in red marrow where blood flow is high



      • (80%) axial skeleton


      • Spine, pelvis, ribs, sternum, calvaria, proximal limb bones


      • Random distribution typical


      • More common proximally in long bones


    • Cortical involvement can occur secondary to direct invasion


  • Size: Ranges from small, solitary lesion to replacement of the entire marrow space


  • Morphology



    • Often infiltrating, elongated, or expansile


    • Focal or regional pattern more characteristic of fracture or arthropathy


    • May not be identifiable on CT


Imaging Recommendations



  • Best imaging tool



    • PET/CT very sensitive for detection of bone metastases



      • FDG PET sensitive for osteolytic lesions and CT sensitive for osteoblastic lesions


      • PET/CT more sensitive and specific than bone scan for delineation of disease and for surgical planning



    • Tc-99m whole body bone scan often used as initial screening due to low cost



      • Sensitivity 80-90%, better than plain radiograph or CT but nonspecific


      • More sensitive than FDG PET for osteoblastic lesions


      • Plain film correlation for further characterization/ambiguity; additional evaluation with CT or MR as necessary


  • Protocol advice



    • FDG PET/CT



      • Position arms above head for whole body scan


CT Findings



  • More sensitive for osteoblastic/sclerotic lesions


  • Insensitive for early infiltrative or osteolytic lesions


  • Early bone infiltration (before destruction) appears as increased attenuation of the normally fatty bone marrow


  • Increased attenuation of lesions generally correlates with lowered FDG uptake


  • Overall sensitivity for bone-seeking cancers: 71-100%


  • Spine



    • Posterior vertebral body almost always involved


    • 80% also in anterior body


    • Enhancement often not detectable


Nuclear Medicine Findings



  • General applications



    • FDG PET/CT more sensitive and specific than bone scan



      • Earlier detection of FDG-avid osteolytic marrow lesions (before cortical changes become evident)


      • Reveals 75% more metastases from breast cancer and to long bones


      • Exceptions include primaries with low FDG avidity, which are typically osteoblastic


      • Osteoblastic metastases include prostate, highly mucinous tumors, and occasionally renal cell carcinoma


      • Sclerotic metastases may not be FDG avid


    • Prediction of bone metastasis in the absence of associated CT findings is hindered by false positives



      • Especially with solitary foci


      • PPV of lesions with negative CT and positive FDG PET: 61%


      • PPV of lesions positive on CT but negative on PET: 17%


    • PET/CT may be cost-effective following screening bone scan for more detailed evaluation of bone metastases


  • Restaging



    • Overall rate of detection of recurrence for FDG PET and CT separately were 47% and 96%


    • Following therapy, “flare” phenomenon may present



      • Treated lesions may have increased FDG uptake during healing and osteoblastic remodeling


      • Bone pain may increase as well


      • Typically arises 4-6 weeks post-therapy and resolves within 3-6 months


      • May show “mixed” response, with a variety of resolved, stable, and new lesions


  • Response to therapy



    • Reduction in SUV of metastatic bone lesions following therapy is highly predictive of response


    • Total lesion glycolysis (TLG) changes were a poor indicator of response duration



      • Possibly due to lack of volume change in treated lesions


  • Findings/anatomy



    • Most common finding: Scattered osseous lesions focused in regions of red marrow, i.e., axial and proximal appendicular skeleton



      • Solitary lesions more likely inflammatory or degenerative than metastatic


      • Linear uptake along ribs (single focus of activity in ribs more likely fracture)


      • Vertebral mets often asymmetric and not confined to endplate


      • Proximal long bone involvement more common; distal long bone mets seen in lung, thyroid, and renal cell carcinoma


    • PET can detect tumors confined to marrow space




      • May have no detectable cortical remodeling and thus not be seen on bone scan


      • Multiple myeloma, lymphoma, leukemia


    • Aggressive tumors with overwhelming osteolytic/osteoblastic activity may be photopenic



      • Renal cell carcinoma, thyroid carcinoma, poorly differentiated anaplastic tumors


      • Occasionally lung, breast, neuroblastoma, myeloma


      • Lytic lesions may become photopenic following radiotherapy, often surrounded by reactive rim of activity


    • “Superscan” MDP bone scan



      • Diffusely increased activity due to disseminated bone lesions


      • May show relative absence of normal renal and soft tissue activity


      • Breast and prostate cancer most common causes


  • Findings by primary

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Sep 22, 2016 | Posted by in MAGNETIC RESONANCE IMAGING | Comments Off on Metastatic Lesions of the Bones

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