High T1 bone lesion

High T1 bone lesions or T1 hyperintense bone lesions are radiological terms to categorise bone lesions with a high signal on T1 weighted images. Apart from the usual description of a bone lesion seen on MRI the terms can be used to categorise 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 a higher signal intensity are referred to as high T1 bone lesions or T1 hyperintense bone lesions also take into consideration that some lesions might display a T1 signal much higher than skeletal muscle or the intervertebral disc due to macroscopic fat or might show only a slightly higher signal such as red marrow ^1-4.

Differential diagnosis

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

• T1 signal related to the skeletal muscle or adjacent intervertebral disc: much higher/slightly higher
• T1 signal similarity to macroscopic fat (matches subcutaneous fat or not)
• signal behaviour on chemical shift imaging (signal drop >20% or signal drop ≤20%)
• contrast enhancement pattern
• focal lesions versus multifocal lesions or diffuse disease

Because of these factors, the differential diagnosis includes ^1-4:

• high T1 matching fat on all sequences
  • focal fatty marrow
  • intraosseous haemangioma
  • intraosseous lipoma
  • degenerative changes Modic type 2
  • osteonecrosis
  • Paget disease of bone
  • postinflammatory focal marrow atrophy
• high T1 different from subcutaneous fat
  • intraosseous ganglion (usually no or peripheral enhancement)
  • a subchondral cyst (usually no or peripheral enhancement)
  • malignant melanoma metastases (usually central or mass-like enhancement)
  • haemorrhagic metastases (usually central or mass-like enhancement)
• slightly high T1 bone lesion
  • red marrow (should show a signal drop in chemical shift imaging)
• fluid-fluid level containing bone lesions
• haemorrhagic bone lesion
• multifocal or diffuse disease with high T1 signal
  • intralesional fat in infiltrative bone lesions ¹
  •  lymphoma (usually not solitary or incidental)
  •  leukaemia (usually not solitary or incidental)
  • radiation therapy
  • spondyloarthropathy
  • multiple intraosseous haemangiomas
  • chronic malnutrition

Practical points

• high T1 signal matching the signal of subcutaneous fat on all sequences →  almost always benign ¹
• high T1 signal is different from subcutaneous fat → might be benign or malignant ¹
• T1 signal slightly higher than skeletal muscle or adjacent intervertebral disc → might be benign and consistent with red marrow ^1,2 or should be worked up as a low T1 bone lesion if not ¹
• high T1 in fluid level or due to haemorrhage can mask the underlying pathology and should be worked up like low T1/high T2 lesions ¹

See also

• low T1 solitary bone lesion
• solitary sclerotic bone lesion
• solitary lucent bone lesion
• solitary mixed density bone lesion
• fluid-fluid levels in bone tumours