FGT — Scattered Fibroglandular Tissue
Scattered fibroglandular tissue (category B) describes breasts where small areas of fibroglandular tissue are interspersed within a predominantly fatty background. Fat is the dominant component, but discrete islands of glandular tissue are present.
Definition
In the BI-RADS v2025 four-tier FGT classification, category B indicates that the breast parenchyma is mostly fatty with scattered areas of fibroglandular tissue occupying approximately 25–50% of the breast volume. The fibroglandular component is clearly not the dominant tissue type, distinguishing it from category C.
Board Pearl
FGT assessment is based on the volume of fibroglandular tissue relative to the total breast volume, not on the enhancement pattern. FGT and BPE are independent descriptors — a breast with scattered FGT can have any level of BPE (minimal to marked).
Imaging Appearance
T1-Weighted (Pre-Contrast)
- Predominantly high-signal fatty tissue with scattered islands of intermediate-to-low signal fibroglandular tissue
- Fibroglandular areas are typically distributed in the central and posterior breast, with fat predominating peripherally and in the retromammary space
T2-Weighted
- Fibroglandular tissue appears intermediate to slightly hyperintense relative to fat (depending on fat suppression)
- Water content within glandular tissue contributes to moderate T2 signal
Post-Contrast (T1W Fat-Saturated)
- Fibroglandular islands demonstrate variable BPE, typically minimal to mild given the limited volume of parenchyma
- Enhancement is assessed independently from FGT amount — scattered FGT with marked BPE is possible (e.g., premenopausal patients, hormone replacement therapy)
DWI
- Normal fibroglandular tissue may show mild diffusion restriction; this is a known source of false positives in breasts with any amount of FGT
- Less problematic in scattered FGT than in heterogeneous or extreme categories due to less background tissue
FGT Category Comparison
| Category | Label | FGT Volume | Masking Risk | Sensitivity Impact |
|---|---|---|---|---|
| A | FGT — Almost Entirely Fatty | <25% | Minimal | Highest sensitivity |
| B | Scattered fibroglandular tissue | ~25–50% | Low | High sensitivity |
| C | FGT — Heterogeneous Fibroglandular Tissue | ~50–75% | Moderate | Reduced sensitivity |
| D | FGT — Extreme Fibroglandular Tissue | >75% | High | Lowest sensitivity |
Clinical Significance
- MRI sensitivity remains high in scattered FGT breasts because the predominantly fatty background provides good contrast for enhancing lesions
- Masking effect is low — small enhancing masses are unlikely to be obscured by scattered parenchyma
- Mammographic correlation: Scattered FGT on MRI generally correlates with ACR density category B on mammography, though MRI and mammographic density assessments may diverge in individual patients
- Cancer risk: Scattered FGT confers a mildly elevated risk compared to almost entirely fatty breasts but is considered average risk in most screening guidelines — it does not independently qualify a patient for supplemental MRI screening
Board Pearl
FGT category does not determine BI-RADS assessment. A breast with scattered FGT and a suspicious enhancing mass is still BI-RADS 4 or 5. FGT is a tissue descriptor, not a finding.
Reporting
FGT category should be reported in the breast composition section of every breast MRI report. It is assessed on the first post-contrast or T1 non-fat-saturated sequence. Report FGT using the standardized BI-RADS letter designation:
Breast composition: Scattered fibroglandular tissue (B).
FGT should be assessed bilaterally and a single overall category assigned. If FGT is asymmetric between breasts, note this but assign the category based on the breast with greater FGT.
Pitfalls
- Confusing FGT with BPE — FGT describes tissue amount on unenhanced images; BPE describes enhancement intensity. A scattered FGT breast with marked BPE during the luteal phase is still category B.
- Over-categorizing as heterogeneous — If fat clearly predominates and fibroglandular tissue appears as discrete islands, this is scattered (B), not heterogeneous (C). The threshold is whether fibroglandular tissue is the minority or co-dominant component.
- Hormonal fluctuation — FGT amount may appear to change across the menstrual cycle due to BPE variation masking or revealing parenchyma. Assess FGT on T1 pre-contrast images to avoid this artifact.
- Post-treatment changes — Chemotherapy, radiation, and anti-estrogen therapy can reduce FGT, shifting a patient from category C to B over time. This should be noted as an interval change.
Board Pearl
Optimal timing for breast MRI in premenopausal women is days 7–14 of the menstrual cycle (week 2) to minimize BPE and allow accurate FGT and lesion assessment. This timing recommendation applies across all FGT categories.
v2025 Changes
The four-tier FGT classification (A–D) is unchanged from the 5th edition. The v2025 update emphasizes that FGT and BPE are independent assessments and reinforces that FGT should be evaluated on pre-contrast sequences when possible to avoid BPE-related misclassification.