Figure 1: Bilateral silicone retroglandular implants are present. The left implant demonstrates clear extracapsular rupture with silicone surrounding the anteromedial portion of the implant. In addition, there are fine serpentine low-signal linear bands in the left implant. These represent the linguine sign or fallen envelope sign, and are indicative of a disrupted implant envelope collapsing and falling into the gel. The right silicone implant is intact with a fibrous capsule. No free silicone is seen within the axillary lymph nodes.

Figure 2: Again, the left breast implant demonstrates extracapsular rupture with free silicone seen anteromedially. The linguini sign can again be appreciated. The right implant is intact with a fibrous capsule.

Extracapsular breast implant rupture.

A dedicated breast coil is used for MR breast imaging, since it provides a better SNR and resolution than a body coil. Imaging is further improved if the patient lies in the prone position with the breasts dependent in the coil. This allows for separation of breast tissue, delineation from the chest wall structures, and decrease in motion artifacts due to respiration. Typically, the simplest image sequences that can be used include a T1-weighted gradient echo localizer, a fast spin echo (FSE) sequence with T2-weighting, and a T2-weighted FSE sequence with water suppression. Since silicone and water have similar signal intensity of T2-weighted imaging, water suppression allows for differentiating cysts and other fluid collections from extruded silicone. T1-weighted images also provide information regarding the presence of any blood components. Because fat and silicone both have bright signal intensity, fat suppression methods can be used to improve silicone visualization and conspicuity.

Implants can either be placed in the retroglandular or subpectoral region. Retroglandular implants stimulate the surrounding tissue to form a fibrous capsule, which is not present in subpectoral implants. Normal implants will have a smooth interface with the adjacent tissue. The implant is surrounded by a T2-weighted low signal intensity fibrous capsule. This dark signal surrounding implants represents a calcified fibrous capsule, a sign commonly seen in long-standing implants. The normal implant may have some implant contour undulations, which represent creases or radial folds in the implant envelope.

The most common complication involving breast implants is capsular contracture. This is the result of the fibrous capsule contracting to produce a hard implant associated with pain. The diagnosis of capsular contracture is based on physical exam, and not on any specific imaging findings. The second most common complication is breast implant rupture, which is divided into intra and extracapsular ruptures. Intracapsular rupture is more common and is caused by the disruption of the implant envelope. It is characterized by the leakage of silicone or saline that is contained within the surrounding fibrous capsule. MRI findings include the linguine sign or fallen envelope sign, which are curvilinear lines within the implant. These lines represent collapsed silicone shell floating within the implant. Extracapsular implant rupture demonstrates rupture of the implant envelope and extrusion of the gel beyond the fibrous capsule. Free silicone is present outside the fibrous capsule, and may extend into the axilla.

References:

1. Kopans, DB. Breast Imaging, 2nd Edition. Philadelphia: Lippincott, 1998. pp. 617-626.
2. Brown, SL, Silverman, BG, and Berg, WA. Rupture of Silicone-Gel Breast Implants: Causes, Sequelae, and Diagnosis. Lancet. 1997; 350: 1531-37.

Location and Date of Scan: New York University Medical Center, New York, Sep 2003.