Fibroglandular Tissue (FGT)
The amount of fibroglandular tissue (FGT) is the relative volume of the breast comprised of fibroglandular structures, assessed subjectively on breast MRI.
Key Distinction from Mammographic Density
- On mammography, density is an x-ray property — the term density should NOT be used to describe MRI FGT.
- On MRI, larger amounts of FGT do not impact diagnostic performance (unlike mammography, where density reduces sensitivity).
- MRI displays FGT in 3 dimensions, providing a volumetric assessment not available on 2D mammography.
Assessment Method
- Assessed subjectively on T1-weighted imaging (with or without fat removal)
- Not reported using percentages (similar to mammographic density assessment)
- Assigned to one of four categories
Four Categories
| Category | Description |
|---|---|
| (A) Almost entirely fatty | Minimal fibroglandular tissue; predominantly fat |
| (B) Scattered fibroglandular tissue | Scattered areas of FGT within fatty background |
| (C) Heterogeneous fibroglandular tissue | Substantial mix of fibroglandular and fatty tissue |
| (D) Extreme fibroglandular tissue | Almost entirely fibroglandular with minimal fat |
Clinical Relevance
FGT level affects:
- Background parenchymal enhancement level (more FGT = typically more BPE)
- The amount of parenchyma at risk for cancer development
- Interpretation context for BPE assessment
Board Pearl
Do NOT use the word “density” to describe FGT on MRI. Density is an x-ray (mammographic) property. On MRI, use “amount” or “volume” of fibroglandular tissue.