Table 1.
Key concepts and methods in the field of bone marrow adiposity.
| Concept or method | Definition | Recommended terms and abbreviations | Further details |
|---|---|---|---|
| Bone marrow adiposity | The phenomenon of fat storage within the bone marrow (BM), primarily within BM adipocytes. | • Bone marrow adiposity (BM adiposity; BMA) • Yellow marrow; red marrow; fatty marrow (Not abbreviated) |
Table 2 |
| Bone marrow adipocytes | The cells within the BM whose primary function is lipid storage. | • Bone marrow adipocyte (BM adipocyte; BMAd) | Table 3 |
| Bone marrow adipose tissue | The functionally integrated tissue formed collectively by BM adipocytes | • Bone marrow adipose tissue (BMAT) • Bone marrow fat (BM fat) |
Table 4 |
| Site-specific differences (BMAd subtypes) | The concept that BM adipocytes have distinct morphological, molecular and functional characteristics, depending on their skeletal location. This may also apply to BMAd progenitors. | • Constitutive or Regulated BMAT or BMAd (cBMAT, cBMAd; rBMAT, rBMAd) • Use “distal” or “proximal” to denote BMAT or BMAd location within long bones; and bone-specific terms to denote skeletal site (e.g., femoral, tibial, vertebral, etc…) |
Table 5 |
| Stem and progenitor cells | The self-renewing, multipotent progenitor cells within the BM that give rise to adipocytes, osteoblasts, chondrocytes, and fibroblasts. | • Skeletal stem cell (SSC) • Bone marrow stromal cell (BMSC) • Do not refer to bone marrow/mesenchymal “stem” cells (this is a misnomer) |
Table 6 |
| Histo-morphometry | Use of histomorphometry to quantify bone marrow adiposity, either on a per-adipocyte level (e.g., Ad.Ar, Ad.Dm, Ad.Pm)* or a whole-tissue level (e.g., adipocyte density, adipose area, adipose volume). | • Adipocyte area (Ad.Ar, μm2) • Adipocyte diameter (Ad.Dm, μm) • Adipocyte perimeter (Ad.Pm, μm) • Adipocyte density or Adipocyte Number* (N.Ad relative to Ma.Ar, Ma.V, T.Ar or TV) • Adipose area* (Ad.Ar relative to Ma.Ar, T.Ar; report as %) • Adipose volume* (Ad.V relative to Ma.V or TV; report as %) |
Table 7 |
| Magnetic resonance imaging or spectroscopy (MRI/MRS) | Use of proton-based MRI/MRS to quantify the proportion or absolute amount of fat within the BM. Typically in vivo, volumetric measurements. | • Fat fraction (FF, %) • Bone marrow fat fraction (BMFF, %) • Proton density fat fraction (PDFF, %) |
Table 8 |
| Computed tomography | Use of CT to estimate BM fat fraction, or μCT to measure BMAT volume or BMAd density. Typically done ex vivo using contrast agents but can also be done in vivo. | • FF (%) or BMFF (%) • Adipose area per marrow area*(Ad.Ar/Ma.Ar, %) • Adipose volume per marrow volume* (Ad.V/Ma.V, %) • Adipocyte density* (N.Ad/Ma.V or N.Ad/M.Ar) |
Table 9 |
These concepts and methods were identified through a systematic literature search, as described in the legend to Figure 1. The recommendations include 26 unique terms and 35 abbreviations. Abbreviations used in this table (*) are defined as follows: N.Ad, adipocyte number; Ad.Ar, total adipocyte area; Ad.V, total adipocyte volume; Ma.Ar, marrow area; Ma.V, marrow volume; T.Ar, tissue area; TV, tissue volume. Further details for each concept/method are provided in the indicated tables and in the main text.