Masses
A mass is a 3-dimensional, space-occupying structure with a defined shape and convex-outward contour.
Definition
Enhancing masses are characterized morphologically by shape, margin, and internal enhancement pattern. These features are assessed on the early post-contrast series (60–120 seconds after contrast). For some masses, T2 signal intensity and/or kinetics may also be useful.
Required Descriptors
A mass description should include at minimum: shape + margin.
When they influence assessment, also describe:
- Internal enhancement pattern
- T2 signal intensity
- Kinetics (when morphology is not definitively benign or suspicious)
Descriptor Categories
1. Shape
| Descriptor | Suspicion |
|---|---|
| Mass Shape — Oval | Benign-favoring |
| Mass Shape — Lobulated | Intermediate |
| Mass Shape — Round | Intermediate |
| Mass Shape — Irregular | Suspicious |
2. Margin
| Descriptor | Suspicion |
|---|---|
| Mass Margin — Circumscribed | Benign-favoring |
| Mass Margin — Indistinct | Suspicious |
| Mass Margin — Spiculated | Most suspicious |
3. Internal Enhancement Pattern
| Descriptor | Suspicion |
|---|---|
| Mass Enhancement — Homogeneous | Can be benign or malignant |
| Mass Enhancement — Dark Internal Septations | Benign-favoring (if shape/margin support) |
| Mass Enhancement — Heterogeneous | Suspicious-favoring |
| Mass Enhancement — Thick Rim Enhancement | Suspicious |
4. T2 Signal Intensity
| Descriptor | Notes |
|---|---|
| Mass T2 Signal — Hyperintense | Benign-favoring in combination |
| Mass T2 Signal — Not Hyperintense | Nonspecific |
The <2% Cancer Risk Combination
Board Pearl
A mass with ALL four of the following features has a likelihood of malignancy ≤ 2%:
- Oval shape
- Circumscribed margin
- Homogeneous enhancement OR dark internal septations
- T2 hyperintense signal
All four must be present. If ANY feature is missing or more suspicious, the <2% threshold does not apply.
Mass vs. Non-Mass Enhancement
When deciding between mass and NME:
- Intervening tissue or fat between enhancing components suggests NME
- NME-type distribution pattern suggests NME
- A mass has a defined 3D shape with convex-outward contour
v2025 Changes
- “Focus” removed: Small dots of enhancement formerly called “focus” are no longer a lexicon category. Characterize as small mass or focal NME using standard criteria.
- “Lobulated” reintroduced: Previously folded into the oval category; now a separate shape descriptor.
- “Indistinct” replaces “irregular” margin: Changed to avoid confusion with “irregular” shape and to harmonize with other modality margin descriptors.
Related
- Mass Shape — Oval
- Mass Shape — Lobulated
- Mass Shape — Round
- Mass Shape — Irregular
- Mass Margin — Circumscribed
- Mass Margin — Indistinct
- Mass Margin — Spiculated
- Mass Enhancement — Homogeneous
- Mass Enhancement — Dark Internal Septations
- Mass Enhancement — Heterogeneous
- Mass Enhancement — Thick Rim Enhancement
- Mass T2 Signal — Hyperintense
- Mass T2 Signal — Not Hyperintense
- Non-Mass Enhancement
- Enhancement Kinetics
- Breast MRI Lexicon Overview