Chapter 9 Breast Implants and the Reconstructed Breast
Implant Types
The most common breast implants are single-lumen and filled with either silicone or saline. Silicone implants are composed of a silicone elastomer shell filled with silicone made from a synthetic polymer of cross-linked chains of dimethylsiloxane that makes the implant soft and movable (Box 9-1 and Fig. 9-1). The outer envelope can be textured or smooth, polyurethane-coated or uncoated. The inner silicone can be a gel, a liquid, or a solid form. Saline implants are composed of an outer silicone shell and an inner envelope filled with saline (Fig. 9-2A to D). Of note, newer generation silicone implants have had a very small rupture rate in augmentation patients. Double- or triple-lumen implants have two or more envelopes inside one another, and each can contain saline or silicone gel. A common double-lumen implant is the saline outer, silicone inner implant. More recent common double-lumen implants have silicone outer and saline inner components. All implants are placed behind the breast tissue, and some implants are placed behind the pectoralis muscle.
Mammography of Normal Implants
A normal silicone implant is quite dense and completely opaque, and obscures and displaces much of the surrounding breast tissue. On mammography the implant appears as a smooth white oval opacity near the chest wall (Fig. 9-3). The pectoralis muscle curves over the implant in subpectoral implants and lies underneath the implant in subglandular implants. A silicone gel-filled implant is not as compressible as breast tissue and can be ruptured if compressed too hard during mammography or closed capsulotomy. Because limited compression decreases visualization of the surrounding breast tissue for breast cancer screening, the Mammography Quality Standards Act (MQSA) recommends four views of each implanted breast. Two views are implant-displaced views, in which the technologist pinches the breast tissue in front of the implant to compress it, and two views include the implant but do not use much compression (Box 9-2). Breast tissue is evaluated on the implant-displaced views; implant integrity is evaluated on limited-compression mammograms in which the implant is surrounded by noncompressed breast tissue. Even with the implant-displaced views, the radiologist sees only about 80% of the breast tissue because it is hidden by the implant.
Box 9-2 Mammography of Implants
CC, craniocaudal; ML, mediolateral; MLO, mediolateral oblique.
If an implant ruptures, the surgeon removes the ruptured implant but does not always remove the fibrous capsule. If the fibrous capsule has calcified, the mammogram shows dystrophic calcifications in a sheetlike curvilinear pattern because they reside in the retained fibrous capsule. These calcifications can be hard to distinguish from cancer and can prompt biopsy (see Fig. 9-6B). Another specific type of capsular calcification that can be mistaken for cancer and will sometimes prompt biopsy is from calcifying polyurethane-covered implants. These implants are covered with a spongelike material, and when they calcify produce a typical fine meshlike calcification that can mimic ductal carcinoma in situ (see Fig. 9-6C and D).
Implant Complications and Rupture
Implant Rupture
Table 9-2 Implant Rupture Types
Rupture Types | Silicone Location | Envelope Status |
---|---|---|
Intracapsular rupture | Fibrous capsule contains silicone gel | Envelope ruptured |
Extracapsular rupture | Silicone gel outside fibrous capsule | Envelope ruptured |
Gel bleed (controversial) | Silicone outside envelope | Envelope intact |
Implant Imaging
Mammography
A retrospective review of screening mammograms in 350 asymptomatic women with breast implants showed an incidence of asymptomatic implant rupture of 5%. Mammography shows extracapsular rupture as silicone extravasation outside the implant envelope with blobs of silicone in the breast tissue (Fig. 9-8A and B), within implant ducts, or as a contour abnormality caused by extruded silicone in contiguity with the implant (Table 9-3). After extracapsular rupture, the surgeon removes the implant. Removal of all extravasated silicone is often impossible without removing much of the breast tissue, so the surgeon may leave some extravasated silicone in the breast. Later, when a new silicone implant is placed, residual silicone from the old ruptured implant makes it impossible to tell on mammography if the new implant has ruptured (see Fig. 9-8C). Silicone within axillary lymph nodes implies extravasation of silicone outside the fibrous capsule, because the silicone has traveled to the lymph nodes. This means that there must be an extracapsular rupture as well (see Fig. 9-8D).
Silicone implant contour lobulation indicates either capsular contracture, herniation of an intact implant envelope through a break in the surrounding fibrous capsule, or a contained implant leak (Table 9-4). Because intracapsular rupture is defined as implant rupture with silicone gel still contained within an intact fibrous capsule, mammography may show an intracapsular rupture as a normal-looking or bulging implant, depending on the shape of the fibrous capsule. Because both implant lobulation and a contained leak have the same mammographic appearance, radiologists use ultrasound and MRI to make the diagnosis of a rupture (see Fig. 9-8E and F). Mammography cannot identify intracapsular ruptures when the implant contour is normal, nor can it show posterior implant ruptures on the chest wall.
Table 9-4 False-Positive Imaging Findings for Rupture
Imaging Modality | Sign | Differential Diagnosis |
---|---|---|
Mammography | Implant contour deformity | |
Intraparenchymal silicone | Previous leak with the ruptured implant removed | |
Ultrasound | Stepladder sign | |
MRI |