Low T1 bone lesion

Low T1 bone lesions or T1 hypointense bone lesions are radiological terms to categorize bone lesions according to their visually perceived low signal on T1 weighted images. Apart from the usual description of a bone lesion seen on MRI they are used to categorize incidentally found solitary bone lesions in the Bone Reporting and Data System (Bone-RADS) ¹.

The lesion signal intensity on T1 weighted images is usually compared to the adjacent skeletal muscle or intervertebral disc ¹ and lesions with similar or lower signal intensity are referred to as low T1 bone lesions or T1 hypointense bone lesions ^1,2.

Differential diagnosis

The differential diagnosis of low T1 lesion can be narrowed down according to the following factors ^1-3:

• the associated T2 signal also evaluated in relation to the skeletal muscle or adjacent intervertebral disc
• the presence of specific features indicating an aggressive nature of the lesion
• focal lesions versus multifocal lesions or diffuse disease

The differential diagnosis comprises a vast list of bone lesions including the following ^1-4:

• high T2 signal
  • geode/subchondral cyst
  • enchondroma
  • osteochondroma
  • non-ossifying fibroma
  • fibrous dysplasia
  • indeterminate bone lesion
  • atypical intraosseous hemangioma
  • benign notochordal cell tumor (BNCT)
  • bone marrow edema/fractures
  • Paget disease
  • giant cell tumor
  • aneurysmal bone cyst
  • chondroblastoma
  • chondromyxoid fibroma
  • osteoid osteoma
  • osteoblastoma
  • osteosarcoma
  • Ewing sarcoma
  • chondrosarcoma
  • lytic bone metastases
  • multiple myeloma (multifocal)
  • lymphoma (usually multifocal)
• low T2 signal
  • enostosis
  • non-ossifying fibroma
  • sclerosing bone dysplasia
  • bone cement
  • sclerotic bone metastases
  • mixed lytic and sclerotic bone metastases
  • Paget disease
  • myelofibrosis (multifocal)
  • lymphoma (usually multifocal)

Practical points

• low T1 bone lesions with aggressive features are generally considered suspicious or in need of treatment

See also

• high T1 bone lesion
• solitary sclerotic bone lesion
• solitary lucent bone lesion
• solitary mixed density bone lesion
• fluid-fluid levels in bone tumors
• low endplate signal on T1