Other Findings — Typically Benign
Other findings typically benign is a BI-RADS v2025 MRI lexicon category encompassing nine entities that are generally benign on breast MRI and may or may not warrant reporting. Accurate recognition of these findings prevents unnecessary biopsy recommendations and avoids false-positive callbacks that increase patient anxiety and healthcare costs.
These findings are distinct from the primary MRI descriptors (Masses, Non-Mass Enhancement, Focus) and are assessed separately in the structured report. When identified in isolation without other suspicious features, they should generally be classified as BI-RADS Category 2 — Benign.
Nine Other Findings
| Finding | Key Feature | T1 Signal | T2 Signal | Enhancement |
|---|---|---|---|---|
| Other Finding — High T1 Duct Signal | Bright ducts pre-contrast (blood/protein) | High | Variable | None or minimal |
| Other Finding — Cysts | Circumscribed, fluid-filled | Low | Very high | None (thin peri-cystic rim acceptable) |
| Other Finding — Postoperative Collections | Hematoma/seroma at surgical site | Variable (age-dependent) | High | Peripheral rim only |
| Other Finding — Post-Therapy Skin and Trabecular Thickening | After surgery/radiation | Isointense | Variable | Variable diffuse skin |
| Other Finding — Non-Enhancing Mass | Solid mass without enhancement; benign | Variable | Variable | None |
| Other Finding — Signal Void | Susceptibility from metallic clip/foreign body | Signal void | Signal void | None |
| Other Finding — Fat Necrosis | Fat at trauma/surgery site; variable enhancement | High (fat signal) | Variable | Variable — rim or none |
| Other Finding — Hamartoma | Fat + FGT within pseudocapsule | Mixed (fat + soft tissue) | Mixed | Enhances like normal FGT |
| Other Finding — Enhancing Skin Lesions | Moles, keloids, skin cysts | Variable | Variable | Avid but confined to skin |
Imaging Appearance — Key Patterns
Pre-Contrast Assessment (T1 and T2)
Several of these findings are diagnosed primarily on pre-contrast sequences, making it critical to review T1-weighted and T2-weighted images before examining subtraction images:
- High T1 duct signal: diagnosed exclusively on pre-contrast T1 — appears as linear/branching high signal following the ductal distribution. Must not be confused with enhancing duct on subtraction.
- Cysts: classic very high T2 signal with low T1 signal and sharp margins. Complicated cysts may show intermediate T1 signal (proteinaceous or hemorrhagic content).
- Fat necrosis: follows fat signal on all sequences — high T1, intermediate T2 with fat suppression dropout. Oil cysts show a pathognomonic fat-fluid level.
Post-Contrast Assessment
- Non-enhancing masses are definitionally benign on MRI — the absence of enhancement excludes clinically significant malignancy in treatment-naïve patients.
- Hamartomas enhance in proportion to their glandular tissue component, matching adjacent Fibroglandular Tissue — the classic “breast within a breast” appearance.
- Postoperative collections may show thin, smooth peripheral rim enhancement that is expected and benign.
Differential Diagnosis — Pitfalls Mimicking Malignancy
| Benign Finding | Malignant Mimic | Distinguishing Feature |
|---|---|---|
| Complicated cyst with thin rim | Thick Rim Enhancement mass | Thin smooth rim (“solar eclipse” sign) vs thick irregular rim; T2 signal of contents |
| Fat necrosis with rim enhancement | Irregular enhancing mass | Central fat signal on T1; clinical history of trauma/surgery |
| Postoperative seroma | Recurrent tumor at lumpectomy site | Timeline (early post-op = expected); progressive enhancement over months is suspicious |
| Enhancing skin lesion | Dermal metastasis / inflammatory carcinoma | Confined to skin surface; no parenchymal extension; correlate with clinical exam |
| High T1 duct signal | Enhancing duct (suspicious) | Present on pre-contrast T1 only; absent on subtraction images |
| Non-enhancing mass | Post-NAC residual tumor | Always check clinical history — biopsy-proven cancer post-chemotherapy may persist as non-enhancing mass |
Clinical Significance and Management
- When these findings are identified in isolation with no other suspicious features, they warrant BI-RADS Category 2 — Benign assessment.
- When a typically benign finding coexists with a suspicious finding, the assessment should be driven by the most suspicious finding — the benign finding is reported descriptively but does not influence category.
- Reporting is optional for some of these findings (e.g., signal voids from known clips, uncomplicated simple cysts) unless they are new, changing, or clinically relevant.
Pitfalls and Common Mistakes
- Confusing high T1 duct signal with enhancing duct: Always check the pre-contrast T1 — if ducts are bright before contrast, they are not truly enhancing. Failure to review pre-contrast images is the most common source of false positives.
- Overcalling thin peri-cystic enhancement: A thin smooth rim around a cyst is a benign finding. Only thick, irregular rim enhancement with uneven inner contour is suspicious.
- Ignoring clinical context for non-enhancing masses: While non-enhancing masses are benign in treatment-naïve patients, this rule does not apply after neoadjuvant chemotherapy.
- Fat necrosis mimicking malignancy: Early fat necrosis may show irregular enhancement and restricted diffusion. The key is identifying central fat signal on T1 and correlating with history of trauma, surgery, or radiation.
- Signal voids causing concern: Biopsy clips produce blooming artifact on gradient echo sequences. Documenting clip placement history prevents unnecessary workup.
Board Pearl
Non-enhancing solid masses are benign on MRI, with one critical exception: a biopsy-proven malignancy after neoadjuvant chemotherapy that persists as a mass but no longer enhances. Always check clinical history before dismissing a non-enhancing mass.
Board Pearl
Thin peri-cystic enhancement around cysts is benign — distinguish it from thick rim enhancement of suspicious masses. Look at the inner contour: smooth (“solar eclipse” sign) = benign peri-cystic; uneven inner margin = suspicious thick rim.
Board Pearl
High T1 duct signal is a pre-contrast finding caused by blood or proteinaceous debris within ducts. It is NOT enhancing duct and does NOT warrant biopsy. The definitive test: check subtraction images — true enhancement will persist, T1 bright ducts will subtract out.
Board Pearl
Hamartoma is diagnosed by the pathognomonic “breast within a breast” sign — a well-circumscribed mass containing both fat and glandular tissue surrounded by a thin pseudocapsule. It is the only breast mass that reliably contains macroscopic fat intermixed with enhancing FGT.
Edition Conflict
In the 5th edition, rim enhancement was listed as an internal enhancement pattern for masses without distinguishing thin benign from thick suspicious types. BI-RADS v2025 explicitly separates thin peri-cystic enhancement (benign, listed under Other Findings) from Thick Rim Enhancement (suspicious mass descriptor). Use v2025 terminology for current practice.
v2025 Changes from Prior Editions
- The category “Other Findings Typically Benign” is formalized as a distinct lexicon section in v2025, consolidating findings previously scattered across different parts of the atlas.
- Enhancing skin lesions are explicitly added to prevent unnecessary parenchymal workup of dermal findings.
- The distinction between thin peri-cystic enhancement (benign) and thick rim enhancement (suspicious) is new and clinically important.
- Non-enhancing mass is given greater emphasis as a reliably benign entity, with the post-NAC caveat clearly stated.