Breast Implants — Multimodality Assessment
Implant Types
Materials
| Type | Key Features |
|---|---|
| Silicone (more common) | Semipermeable silicone polymer shell; smooth or textured outer surface; silent rupture common |
| Saline | More radiolucent; has a valve (fluid can be added/removed); rupture clinically evident (deflates) |
Implant Shell (“Silicone Sequences” on MRI)
- Shell = elastomer cell/envelope/membrane = solid silicone polymer
- Can be smooth or textured outer surface (theory: texturing reduces implant rotation and capsular contracture)
- Cannot tell on imaging whether textured or smooth
Lumen Types
- Single lumen: most common
- Double lumen: inner lumen (silicone) + outer lumen (saline); also silicone-silicone double lumen
- Can be seen as silicone-silicone; outer lumen appears radiolucent
Implant Position
| Position | Description |
|---|---|
| Retroglandular/Subglandular | Anterior to pectoralis, behind glandular tissue |
| Prepectoral | Anterior to the pectoralis (same as retroglandular/subglandular) |
| Subpectoral/Retropectoral/Submuscular | Posterior to pectoralis major |
Tissue Expanders
- Expander implant has a metal valve (saline added over time)
- May not be MRI compatible or may cause too much artifact
Direct Injection Materials
| Substance | Imaging Appearance |
|---|---|
| Silicone injections | Dense masses on mammo, some with peripheral calcs and/or fat necrosis areas |
| Paraffin injections | Initially masses representing fluid collections; later masses representing parafffinomas with calcs and AD |
| Polyacrylamide gel | Variable |
The Fibrous Capsule
- When implant is placed → inflammatory reaction → forms fibrous capsule
- Capsule has a smooth inner surface + creates potential space (between fibrous capsule and implant shell)
- Fluid can be seen in this space
- Calcifications often develop within the capsule
Implant Complications
1. Capsular Contracture
- Most common complication of breast implants
- Most common in silicone implants in a subglandular location
- Clinical diagnosis (NOT imaging diagnosis)
- Fibrous capsule contracts around implant → breast becomes hard and implant’s movement is limited
- In severe contracture: implant may not be able to be displaced for imaging → usually need to take out the implant and capsule to fix
2. Gel Bleed
- Silicone molecules can pass through the intact semipermeable membrane shell without rupture
- Gel can coat the exterior surface of the implant shell
- Can travel to lymph nodes even without rupture
- May or may not be symptomatic
3. Implant Rupture
- Main predisposing factor = age of the implant
- Can be spontaneous or from external source
- Rupture during mammography is rare
Saline Implant Rupture:
- Obvious clinically (breast deflates)
- Shell is collapsed on mammography
Silicone Implant Rupture — Two Types:
Intracapsular Rupture
- Implant shell is disrupted but silicone is still contained by the fibrous capsule
- Patients usually asymptomatic
- Not apparent on clinical exam or mammography
- US: NOT very sensitive or specific; finding suggestive = multiple parallel echogenic lines within sonolucent silicone = “stepladder sign”
- MRI is the most sensitive and specific modality
MRI Signs of Intracapsular Rupture:
| Sign | Description |
|---|---|
| Linguine sign | Curvilinear low intensity signal within implant = collapsed elastomer shell floating in silicone, contained by fibrous capsule |
| Subcapsular line sign | Silicone has leaked out of the ruptured shell but shell has not collapsed; silicone on BOTH surfaces of ruptured shell |
| Inverted teardrop/noose/keyhole sign | Silicone leakage within a fold of the shell (indicates rupture) |
| Radial folds | NORMAL — do NOT indicate rupture; contiguous with shell; thicker than intracapsular rupture (double layer of shell) |
Pitfall
Radial folds are NORMAL — don’t mistake for intracapsular rupture. Lines of a radial fold are thicker than the collapsed shell in intracapsular rupture (radial folds = double layer of shell). The shell can fold into the implant and have long, complex folds with the shell still intact. Must be contiguous with the shell.
Extracapsular Rupture
- Silicone has leaked outside the fibrous capsule
- Usually not a hard diagnosis on any modality
- Silicone is higher density than breast parenchyma on mammo
- Follow contour of implant → look for abnormalities or globular/linear silicone tracking outside fibrous capsule
- Silicone granulomas can form in breast tissue; silicone can extend into ducts
- US appearance: “snowstorm” appearance (classic); but may present atypically as hypoechoic regions, complex cystic lesion, or shadowing mass
- MRI: extracapsular silicone has low T1 signal on fat sat T1 and high signal on water-suppressed T2
4. Contour Irregularities
- Bulge: focal protrusion of implant within intact fibrous capsule (capsule not disrupted)
- Herniation: portion of implant extends through a defect in the fibrous capsule
- Opposite of intracapsular rupture (implant intact but fibrous capsule disrupted)
- May present as palpable mass
- Mammography alone cannot differentiate bulge from herniation and cannot exclude rupture
Peri-Implant Fluid
- Small amount adjacent to implant is normal
- Large or increasing amounts may be due to:
- Implant rupture, infection, localized/generalized edema, BIA-ALCL, inflammatory carcinoma
- Hematoma, seroma, mastitis, abscess (in early post-placement period)
Imaging of Women with Implants
Mammography
- Sensitivity reduced: 45% in women with implants vs. 66% in women without
- Perform: CC and MLO implant-displaced views + non-displaced views
- Subpectoral implants are easiest to displace
- Implants may obscure between 22–83% of breast tissue
Ultrasound for Rupture
- Sensitivity: 73.7%, Specificity: 87.8%
- First-line for BIA-ALCL evaluation
MRI for Rupture
- Most sensitive and specific modality
- Silicone-specific sequences (suppress fat AND water → only silicone is bright)
Special Implant Issues
Silicone Granulomas
- Usually high density on mammo
- May be circumscribed or indistinct
- Most often identifiable as silicone, but in some cases suspicious for malignancy on mammo (if less dense)
Explantation Consequences
- Scarring and fat necrosis can produce a mass-like appearance
- Fibrous capsule often calcifies → if not completely removed, residual calcs may look suspicious
- Benign palpable findings related to implant: implant fold, valve, implant bulge or herniation, dense free silicone, dense silicone granuloma, dense silicone-containing lymph node, oil cysts, characteristically benign calcs (dystrophic, lucent-centered)
Saline Implant “Baffling”
- Two lumens and a series of shells of increasing size nested together
- Unusual appearance — don’t mistake for pathology
Acellular Dermal Matrix (ADM)
- Surgical mesh of human or animal skin with cells removed (only collagen supporting structures remain)
- Creates artificial internal soft tissue support
- Higher complication rate than implant alone
- Better cosmesis; may prevent malpositioning and capsular contracture
2022 FDA Breast Implant Guidelines
- First screening exam: 5 years after implantation
- Subsequent: every 2–3 years
- Can use US or MRI for screening
Breast Implant Illness Syndrome (BII)
- Symptoms: arthralgias, fatigue, hair loss, skin changes, lethargy
- No specific imaging or lab tests
- Explantation may or may not improve symptoms