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surrounding capsule, as described in Chapters 3 and 5. Rupture involving only the silicone shell, with free silicone gel still contained by the surrounding fibrous capsule, are defined as intracapsular rupture. Disruption of both the implant shell and fibrous capsule allows silicone access to breast tissue and is defined as an extracapsular rupture. Normal silicone fluid diffusion is detectable only rarely by imaging examinations.

Other terms associated with loss of shell or fibrous capsule integrity are also in common usage. Herniation indicates focal bulging of an intact implant through a defect in the surrounding fibrous capsule. Extrusion implies a sudden flow of silicone gel through defects in the implant shell and fibrous capsule, which may occur with traumatic events. Infiltration is a slow movement of extracapsular silicone gel into surrounding breast or other tissue. Extravasation is an inclusive term encompassing extrusion and infiltration, whereas migration refers to extracapsular silicone gel movement away from the implant.

The frequency of implant rupture is unknown. Chapter 5 discusses the reasons for this, which include such factors as the changing composition of implants, the decades-long observation required in some cases, the study of nonrepresentative groups of women with implants, and incomplete or imprecise detection of rupture. Some confusion is also occasionally caused by the separation of rupture into leakage and rupture or disruption categories. Estimates of implant rupture prevalence range from 0.3 to 77%, as reported earlier. Rupture prevalence depends at least in part on implant characteristics such as elastomer shell thickness and strength; thus descriptions of rupture prevalence must consider and identify the types and ''generations" of implants. Breast implant integrity can be evaluated clinically; mammographically; and with computed tomography, ultrasound, and magnetic resonance imaging (MRI).

Mammography

The intact silicone gel-filled implant appears as a radiodense structure sharply circumscribed from surrounding breast tissue. At times, the implant fibrous capsule may be visible just superficially to the implant shell. Dystrophic calcification can be identified in the fibrous capsule (Benjamin and Guy, 1977). Calcification is often seen and could represent a long-term inflammatory response to the breast prosthesis (Barker et al., 1978; Cocke et al., 1985; Ginsbach et al., 1979; Inoue et al., 1983; Koide and Katayama, 1979; Peters et al., 1995d; Redfern et al., 1977; Young et al., 1989). Textured implants may disorganize capsular fibrotic reactions and decrease capsular contracture. Use of textured implants could be a source of a false-positive mammographic diagnosis of rupture. The presence of a textured implant is easily detected by its brush border (Piccoli, 1968). The



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