In the early 20th century, many cosmetic breast prosthetic techniques and materials were used for implants; these included polyvinyl alcohol prostheses, paraffin injections, and injections of free silicone. All of these techniques and materials had notable drawbacks and for the most part were abandoned. Silicone gel breast implants (SGBIs) have been marketed in the United States since 1962. (An intact SGBI is seen in the image below.) The US Food and Drug Administration (FDA) began regulating SGBIs in 1976 with the passage of the Medical Device Amendments. In 1992, after months of public and private meetings, the FDA restricted the use of SGBIs to specific instances of medical necessity, such as those involving patients who had undergone mastectomy. Saline breast implants have replaced SGBIs as the common breast prosthesis. Details of the FDA rulings and current status updates are available at the Breast Implants information section of the FDA Web site.
Inversion recovery magnetic resonance image shows an intact silicone gel breast implant.
The ability to reliably evaluate SGBIs with imaging is important because the findings at clinical examination often are nonspecific. The incidence of implant rupture increases with time, and the long-term systemic effects of SGBIs, if any, remain unclear. The diagnosis of SGBI rupture is useful to clinicians and patients; it aids in surgical decision making and helps the patient gain peace of mind.
This article does not address imaging of the rupture of single-lumen saline implants (which usually is clinically obvious because extravasated saline is rapidly absorbed and breast volume quickly decreases at examination).
The imaging examinations for SGBI rupture are the include MRI, ultrasonography, computed tomography (CT) scanning, and mammography.
Patients should undergo mammography per the American Cancer Society recommendations for breast cancer screening.
Mammography is the most common breast imaging examination and can readily depict extracapsular free silicone. When implant rupture and extravasation is detected at mammography, further imaging studies may not be required. However, screening mammography alone is insensitive for detection of intracapsulr implant rupture, and its findings often are nonspecific in the detection of SGBI rupture.
MRI is the most accurate imaging examination for the evaluation of SGBI rupture.
MRI’s drawbacks include its cost and possible unavailability. It provides a reliable way to assess implant rupture and is highly sensitive for detection of both intracapsular and extracapsular rupture. MRI findings of intracapsular rupture include the keyhole or noose sign, subcapsular line sign, and linguine sign.
Ultrasonography can be used to assess the internal structure of the implant. Common ultrasound signs of intracapsular rupture include the keyhole or noose sign, subcapsular line sign, and stepladder sign. Extracapsular silicone has a distinctive snowstorm or echogenic noise appearance. Ultrasonography is fairly accurate and more available than MRI but is highly operator dependent and has a steep learning curve.
CT scanning can show findings similar to those obtained with MRI, but the modality involves ionizing radiation, and it has not been systematically studied to the extent that MRI has been.