High T1 bone lesion

Last revised by Dr Joachim Feger on 07 Jun 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 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 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

In view 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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