Radiography
Findings
Findings at mammography include the following:
- Rupture with deflation and silicone extravasation
- Measurable periprosthetic opaque band or rim of tissue
- Periprosthetic calcification
- Asymmetry in the size and/or shape of the implant
- Focal implant herniation
Silicone injections and SGBIs can limit the sensitivity of mammography. Implant-displaced views should be obtained, if possible. Comparison with prior images is strongly advised.
Degree of Confidence
When rupture and extravasation are present, confidence is high. However, these findings are uncommon, and other signs are both insensitive and relatively nonspecific. However, when screening mammography performed for other reasons reveals incidental signs of rupture, the sensitivity is high.
Computed Tomography
Findings
With intracapsular ruptures, CT scans show findings analogous to the linguine sign at MRI, and CT can demonstrate the extracapsular spread of silicone. To our knowledge, no findings from large studies examining the effectiveness of CT have been published. Because CT scanning involves ionizing radiation and its multiplanar capabilities are limited, MRI typically is the examination of choice.
Magnetic Resonance Imaging
Findings
MRI can be used to exploit differences in silicone, water, and fat resonance frequencies to deliver high-resolution images of SGBIs.11,13,14 The approximate resonance frequency of silicone is 100 Hz lower than that of fat and 320 Hz lower than that of water. Because the resonance of silicone is similar to that of fat, silicone appears similar to fat on nonselective chemical fat- or water-suppressed images.
On short – inversion time inversion-recovery (STIR) images, the fat signal is suppressed and water and silicone are bright. Water-suppressed STIR sequences produce a silicone-only image. Chemical-shift imaging with the modified 3-point Dixon protocol provides both a silicone-only and a water-and-fat image with a single sequence. The relative appearances of silicone, fat, and water on various types of MRIs are summarized in the following table:
Table. Relative Appearances of Silicone, Fat, and Water
on MRI of SGBI Rupture*
Open table in new window
Table
| MR Pulse Sequence† | Silicone | Fat | Water |
| FSE T2 weighted | Bright | Moderate | Very bright |
| FSE T2 weighted, water suppressed | Bright | Moderate | Dark |
| STIR | Bright | Dark | Very bright |
| STIR fat suppressed | Bright | Dark | Dark |
| Three-point Dixon, silicone only | Bright | Dark | Dark |
| MR Pulse Sequence† | Silicone | Fat | Water |
| FSE T2 weighted | Bright | Moderate | Very bright |
| FSE T2 weighted, water suppressed | Bright | Moderate | Dark |
| STIR | Bright | Dark | Very bright |
| STIR fat suppressed | Bright | Dark | Dark |
| Three-point Dixon, silicone only | Bright | Dark | Dark |
* Adapted, with permission, from Bassett and Jackson.15
† FSE indicates fast spin echo.
While exact protocols differ among institutions, in general, orthogonal-plane imaging with several pulse sequences is performed. Image quality is maximized with the use of a dedicated phased-array breast coil and a high – field-strength magnet; however, in our experience, an adequate examination can also be performed with a low – field-strength, open-sided magnet.
MRI findings include the following:
- Intact single-lumen implants
- Smooth, low – signal-intensity silicone membrane shell
- Low – signal-intensity radial folds in the shell (These may be complex, and they always abut the implant at its periphery and span the gel substance only at periphery.)
- A few internal water droplet signals (common; not a reliable indication of rupture)
- Reactive fluid around textured implants (common; not indicative of rupture)
- Fibrous capsule (dark, ringlike structure around the implant)
- Double-lumen implants - Gradual deflation of the saline chamber over time, which results in complex fold patterns and occasional, nonspecific findings of fluid around the outer capsule of the implant
- Intracapsular rupture
- The linguine sign refers to a collapsed and folded elastomer shell that is floating in gel. This is the most reliable sign of intracapsular rupture.
- The keyhole (ie, teardrop, inverted teardrop, noose) sign refers to the presence of silicone both inside and outside a radial fold.
- Extracapsular rupture10
- Macroscopic extrusion of silicone through the fibrous capsule into the surrounding parenchyma, pectoralis muscle, or lymph nodes is present.
- Findings in intracapsular rupture should be expected.
- Internal rupture of double-lumen implants
- Failure of the inner shell may be depicted as saline droplets that are floating in the silicone gel; this is considered a form of intracapsular rupture.
- The presence of some saline droplets is a normal finding in single-lumen implants.
- Capsular contracture
- Asymmetric, serrated, focal folding of the fibrous capsule that changes the normal ovoid appearance of the implant may be present.
- A transverse diameter of less than twice the anteroposterior depth corresponds well to clinically evident contracture.
Degree of Confidence
MRI has a reported a sensitivity of 76-95% and a specificity of 93-97% in the detection of rupture.
False Positives/Negatives
Extensive gel bleeding can have the same findings as those of an intracapsular rupture, in which the keyhole sign is present and the linguine sign is absent. Some authors believe that a tiny tear is present and that it can be found with diligent examination at surgery. Other authors maintain that microscopic gel bleeding alone is the cause. Radial folds are normal invaginations of the silastic membrane, and they should not be confused with the keyhole sign. Silicone should not be present both inside and outside a radial fold.
Ultrasonography
Findings
Typically, a high-frequency (eg, 10-MHz) transducer is used. Findings may include the following:
- Intact implant
- Smooth, thin, linear membrane
- Sonolucent anechoic interior (most reliable but insensitive finding)
- Reverberation artifact from the proximal membrane wall
- Radial folds possible - Parts of the implant envelope may be connected by scanning adjacent portions of the implant.
- Linear internal echoes - These do not indicate rupture. The abundance of the linear echoes has been evaluated, and their effect in the prediction of rupture is not statistically significant.16
- Intracapsular rupture
- Stepladder sign - This is identified as multiple, discontinuous, parallel, linear echoes in the lumen. It is the most reliable ultrasonographic finding in intracapsular rupture and is analogous to the linguine sign at MRI.
- Echogenic implant lumen
- Focal, prominent, irregular bulge in the implant
- Ill-defined or poorly visualized implant margin
- Extracapsular rupture10
- Snowstorm, or hyperechoic, noise - Intense, homogeneous echogenicity with loss of the posterior detail of free silicone (silicone can replace portions of the implant envelope; be extruded into the breast parenchyma, forming nodules; and migrate to lymph nodes)
- Silicone masses (granulomas) - The same hyperechoic noise pattern as above; possibly hyperechoic or hypoechoic and similar to other breast lesions (including carcinoma) or nearly sonolucent and similar to breast cysts (hyperechoic noise is often near or around cystic-appearing masses)
- Snowstorm pattern in involved axillary lymph node
- Indeterminate
- Coarse echogenic aggregates - Occurred in 41% of surgically confirmed implant ruptures in one study17 . These have also been found to occur in approximately the same percentage of implants that have been confirmed as intact at surgery.
- Cobwebs - Delicate, short, linear echoes diffusely scattered throughout the implant (most authors consider this finding a normal variant; they also are called "commas" in some reports)
- Smooth focal bulge in the implant
- Peri-implant fluid collections
Degree of Confidence
Sensitivity ranges from 47-74%; specificity, from 55-96%. An anechoic interior, although rare (4 of 64 implants in one series), is a strong indicator of an intact implant.
False Positives/Negatives
Ultrasonography is limited in the evaluation of the posterior implant wall, because of marked beam attenuation caused by silicone. Use of a low-frequency transducer (eg, 5 MHz) can help improve visualization of the posterior wall of the implant and the adjacent soft tissues. Reverberation artifacts from the near-side interface may limit visibility of the superficial implant margins. Prior silicone injections limit visualization of the implant.
More on Breast, Implant Rupture |
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 Imaging: Breast, Implant Rupture |
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References
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Further Reading
Keywords
imaging of silicone gel breast implant rupture, SGBI
