High T1 bone lesions or T1 hyperintense bone lesions are radiological terms to categorize 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 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 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.
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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 behavior 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 hemangioma
- 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)
- hemorrhagic 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
- hemorrhagic bone lesion
- multifocal or diffuse disease with high T1 signal
- intralesional fat in infiltrative bone lesions 1
- lymphoma (usually not solitary or incidental)
- leukemia (usually not solitary or incidental)
- radiation therapy
- spondyloarthropathy
- multiple intraosseous hemangiomas
- 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 hemorrhage 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 tumors