High T1 bone lesion

Last revised by Joachim Feger on 20 Jul 2022

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.

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 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

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